LBNL/PUB-5506

Conceptual Design Report of the Top-Off Upgrade of the Advanced Light
Source at Lawrence Berkeley National Laboratory

Berkeley, December 23, 2004

![](media/image1.png){width="1.3298611111111112in"
height="0.8055555555555556in"}

Lawrence Berkeley National Laboratory,

> 1 Cyclotron Road, Berkeley, CA 94720

This work was supported by the Director, Office of Science, Office of
Basic Energy Sciences, of the U.S. Department of Energy under Contract
No. DE-AC03-76SF00098.

[1 Motivation 5](#motivation)

[1.1 Science at the Forefront 5](#science-at-the-forefront)

[1.2 Increased Brightness with Top Off and Advanced Undulators
8](#increased-brightness-with-top-off-and-advanced-undulators)

[1.3 More Beamlines to Exploit the Brightness
11](#more-beamlines-to-exploit-the-brightness)

[1.4 Advantages to the user programs
12](#advantages-to-the-user-programs)

[2 Overall Scope of Project, Introduction of Subproject Parts
13](#overall-scope-of-project-introduction-of-subproject-parts)

[2.1 Present injection mode 14](#present-injection-mode)

[2.2 Parameters and operation with Top-off
17](#parameters-and-operation-with-top-off)

[2.3 Introduction of the Subparts of the CDR
18](#introduction-of-the-subparts-of-the-cdr)

[3 Detailed Description of all Parts of the Top-off Upgrade
20](#detailed-description-of-all-parts-of-the-top-off-upgrade)

[3.1 User requirements 20](#user-requirements)

[3.1.1 Operational Tests 21](#operational-tests)

[3.2 Radiation Safety 25](#radiation-safety)

[3.2.1 Top-off Radiation Issues/challenges
25](#top-off-radiation-issueschallenges)

[3.2.2 Current Radiation Practices and Results
25](#current-radiation-practices-and-results)

[3.2.3 Top-off Radiation Issues/Challenges
29](#top-off-radiation-issueschallenges-1)

[3.2.4 Collimation/Scraper System 36](#collimationscraper-system)

[3.2.5 Radiation Monitors 39](#radiation-monitors)

[3.2.6 Top Off Mode, Radiation Safety System
40](#top-off-mode-radiation-safety-system)

[3.3 Accelerator Physics Studies 45](#accelerator-physics-studies)

[3.3.1 Vertical emittance reduction in the Storage ring
45](#vertical-emittance-reduction-in-the-storage-ring)

[3.3.2 Operation with smaller vertical gaps in the storage ring
49](#operation-with-smaller-vertical-gaps-in-the-storage-ring)

[3.3.3 Linac to booster transfer efficiency
50](#linac-to-booster-transfer-efficiency)

[3.3.4 Booster to Storage ring transfer efficiency
50](#booster-to-storage-ring-transfer-efficiency)

[3.3.5 Minimizing radiation levels 52](#minimizing-radiation-levels)

[3.4 Injector Reliability 54](#injector-reliability)

[3.4.1 Scope 54](#scope)

[3.4.2 Injection System Components 54](#injection-system-components)

[3.4.3 Injector Operating Mode 55](#injector-operating-mode)

[3.4.4 Injection System Component Failures
55](#injection-system-component-failures)

[3.5 Pulsed Magnets 59](#pulsed-magnets)

[3.5.1 Introduction 59](#introduction)

[3.5.2 Pulsed magnet operation 59](#pulsed-magnet-operation)

[3.5.3 Booster bumps analysis: 62](#booster-bumps-analysis)

[3.5.4 Booster Fast extraction Kicker:
68](#booster-fast-extraction-kicker)

[3.5.5 Booster and Storage ring Thick and Thin septum magnets
72](#booster-and-storage-ring-thick-and-thin-septum-magnets)

[3.5.6 Storage ring 'fast' bump magnets
90](#storage-ring-fast-bump-magnets)

[3.5.7 Summary of pulse magnets study:
93](#summary-of-pulse-magnets-study)

[3.6 DC and Slow Ramped Magnets 94](#dc-and-slow-ramped-magnets)

[3.6.1 Power Supplies 94](#power-supplies)

[3.6.2 DC Cabling 95](#dc-cabling)

[3.6.3 AC Power 96](#ac-power)

[3.7 Timing System 97](#timing-system)

[3.7.1 Injector Timing 97](#injector-timing)

[3.7.2 User Gating System 97](#user-gating-system)

[3.8 Booster RF System 98](#booster-rf-system)

[3.8.1 Overall System Introduction & Description
98](#overall-system-introduction-description)

[3.8.2 Booster RF Power Requirements for Top-Off Mode of Operation
101](#booster-rf-power-requirements-for-top-off-mode-of-operation)

[3.8.3 Final Amplifier/Transmitter with Controller
104](#final-amplifiertransmitter-with-controller)

[3.8.4 High Voltage Power Supply 104](#high-voltage-power-supply)

[3.8.5 RF Cavity Window 105](#rf-cavity-window)

[3.8.6 RF Transmission Line 105](#rf-transmission-line)

[3.8.7 Controls & Interlocks 106](#controls-interlocks)

[3.8.8 Utilities 106](#utilities)

[3.8.9 Structure Core Drilling 107](#structure-core-drilling)

[3.8.10 Spares 107](#spares)

[3.9 Diagnostics 108](#diagnostics)

[3.9.1 Booster Diagnostics 108](#booster-diagnostics)

[3.9.2 BTS Diagnostics 113](#bts-diagnostics)

[3.9.3 Storage Ring Diagnostics 118](#storage-ring-diagnostics)

[3.10 Computer Control System 121](#computer-control-system)

[3.10.1 Magnet Power Supplies 121](#magnet-power-supplies)

[3.10.2 BTS Diagnostics 122](#bts-diagnostics-1)

[3.10.3 Booster Diagnostics 122](#booster-diagnostics-1)

[3.10.4 Booster RF 123](#booster-rf)

[3.10.5 Radiation Protection 123](#radiation-protection)

[3.10.6 Collimation Controls 123](#collimation-controls)

[3.10.7 Software Effort 123](#software-effort)

[3.10.8 IOC software effort 123](#ioc-software-effort)

[3.10.9 Control Room Application Development
124](#control-room-application-development)

[3.10.10 New IOCs 124](#new-iocs)

[3.11 AC Power Utilities 126](#ac-power-utilities)

[3.11.1 AC Power Utilities-Booster Ring
126](#ac-power-utilities-booster-ring)

[3.11.2 Description-General 126](#description-general)

[3.11.3 Booster RF AC Power 127](#booster-rf-ac-power)

[3.11.4 Booster to Storage Ring (BTS) 127](#booster-to-storage-ring-bts)

[4 Cost, Schedule, Installation 130](#cost-schedule-installation)

[4.1 Project Organization 130](#project-organization)

[4.2 Work Breakdown Structure 131](#work-breakdown-structure)

[4.3 Cost Estimate 132](#cost-estimate)

[4.4 Draft Schedule 134](#draft-schedule)

[4.5 Installation 139](#installation)

[4.6 Commissioning 140](#commissioning)

[5 Acknowledgments 141](#acknowledgments)

[6 References 142](#references)

[6.1 List of Figures 143](#list-of-figures)

[6.2 List of Tables 146](#list-of-tables)

[7 Appendices 148](#appendices)

[7.1 Parameter List 148](#parameter-list)

[7.1.1 Storage Ring Performance Parameters
148](#storage-ring-performance-parameters)

[7.1.2 Booster Performance Parameters
148](#booster-performance-parameters)

[7.1.3 Technical Parameters 149](#technical-parameters)

[7.2 Full Cost Estimate 150](#full-cost-estimate)

# Motivation

One of the first third-generation synchrotron light sources, the ALS,
has been operating for almost a decade at Berkeley Lab, where
experimenters have been exploiting its high brightness for forefront
science. However, accelerator and insertion-device technology have
significantly changed since the ALS was designed. As a result, the
performance of the ALS is in danger of being eclipsed by that of newer,
more advanced sources. Enhanced brightness is the key not only to
remaining competitive but also to setting a new performance standard.

Significant brightness improvements can be realized in the core soft
x-ray region by going to top-off operation, where injection would be
quasi-continuous. In top-off mode with higher average current, a reduced
vertical emittance and beta function, and small-gap permanent-magnet or
superconducting insertion devices, one to two orders of magnitude
improvement in brightness can be had in the soft x-ray range. These
improvements also extend the high energy range of the undulator
radiation beyond the current limit of 2000 eV. Most important, top-off
avoids the penalty of a much reduced lifetime that would otherwise come
with increased brightness, a penalty that is totally unacceptable to the
user community.

In brief, the ALS upgrade that we are planning includes full-energy,
top-off injection with higher storage-ring current and the replacement
of older first-generation insertion devices with newer state-of-the art
insertion devices and four new application-specific beamlines now being
identified in a strategic planning process. The upgrade will involve no
major disruption to the experimental program of the ALS, since it can be
accomplished in a phased sequence of short (less than 2 month) shutdown
and commissioning periods. The first phase of the ALS upgrade is to
transition to top-off operation with higher beam currents and smaller
vertical beamsizes. It is the top-off upgrade that is the focus of this
report. Before describing the upgrade, some examples of different types
of science that are enabled with higher brightness are presented.

## Science at the Forefront

Exploitation of the high brightness of a third-generation synchrotron
light source translates into four areas: (1) high resolving power for
spectroscopy; (2) high spatial resolution for microscopy and
spectromicroscopy; (3) high temporal resolution for diffraction and
spectroscopy; and (4) high coherence for experiments such as speckle and
lensless imaging. Capabilities in these areas will also enable the ALS
to support the Molecular Foundry, a U.S. Department of Energy Nanoscale
Science Research Center that is now under construction at Berkeley Lab
with construction, equipment installation, and commissioning expected by
the end 2006. The ALS offers a variety of characterization and
diagnostic capabilities applicable to nanoscale science and technology,
including diffraction, photoemission, absorption, and fluorescence
spectroscopy, often with temporal as well as spatial resolution.

The physics of complex materials studied by photoemission with high
energy and high momentum resolution has benefited enormously from the
availability of high brightness sources. Improvement in the energy
resolution from 50 meV to 10 meV has enabled investigation of low-energy
excitations, such as the dispersion "kink" \[1\] and bilayer splitting
in the high T~c~ superconductors \[2\]. Seven photoemission papers have
made it to the "ten most cited physics papers" at one time or another.
Further improvement in resolution down to the meV range will provide
even sharper experimental incisiveness for the understanding of complex
materials ranging from strongly correlated electron systems and magnetic
materials to systems with reduced dimensionality.

Inelastic x-ray scattering (IXS) is a complementary but more demanding
spectroscopy. As a photon-in/photon-out technique, it has the advantage
over photoemission of greater penetration and the ability to look at
bulk properties and buried interfaces. IXS is the only direct probe of
charge-charge correlations that offers momentum resolution. Moreover,
unlike photoemission, it is possible, to apply a magnetic field to the
sample. The disadvantage of IXS is its inherently low cross-section, so
that the state-of-the-art resolution is 250 meV. We have dedicated the
last remaining straight section at the ALS to MERLIN, a new beamline
mainly for IXS that will reach a resolution of 10 meV. (A second
dedicated end station will be for photoemission with sub-meV
resolution). This performance will be achievable only below a photon
energy of 100 eV, so that only momentum transfers close to the
Brillouin-zone center (q=0) can be investigated. To reach the zone edge
it would be necessary to work closer to 1000 eV. This can in principle
be done but only after the upgrade described below.

Understanding fundamental magnetic interactions is at the frontier of
solid-state physics but also driven by the technology of thin-film
magnetic devices. At the ALS we have pioneered the development of new
techniques, one example being magnetic imaging for the elucidation of
exchange bias in the coupling of the antiferromagnetic (AF) to
ferromagnetic (FM) materials that lies at the heart of magnetic spin
valves. This problem could only be solved with our new ability to image
AF and FM domain structures at high spatial resolution, with interfacial
sensitivity, and with elemental and chemical selectivity, by means of
photoemission electron microscopy (PEEM). These techniques are
revolutionizing our understanding of thin-film magnetism \[4-8\], and we
expect PEEM 3, the next generation microscope, to begin commissioning in
2005 \[9\].

Manipulation of spin directly by optical or electrical means leads to
the concept of "spintronics"\[10\]. The fundamental lateral length scale
now shrinks to the magnetic exchange length measured in nanometers with
a temporal scale set by magnetization precession time of picoseconds. On
the horizon are devices such as spin transistors, spin-transfer devices
or even spin-based quantum computers. Together with complementary laser
probes, time-resolved soft x-ray probes will lead to major advances.
Experiments in this domain are brightness limited and are at the edge of
viability at the ALS today. They would become practical with the
enhancements envisioned for this upgrade.

The structure of condensed matter is not static, and to understanding
the behavior of condensed matter at the most fundamental level requires
structural measurements on the time scale on which atoms move. The
evolution of condensed matter structure, via the making and breaking of
chemical bonds and the rearrangement of atoms, occurs on the fundamental
time scale of a vibrational period, \~100 fs. Atomic motion and
structural dynamics on this time scale ultimately determine the course
of phase transitions in solids, the kinetic pathways of chemical
reactions, and even the efficiency and function of biological processes.
A thorough understanding of such dynamic behavior is a first step to
being able to control structural evolution and will have important
scientific applications in solid-state physics, chemistry, materials
science, and biology \[11\]. The tremendous potential scientific impact
of this research area is largely unfulfilled, owing to the inadequacy of
present zeroth-generation short-pulse x‑ray sources (roughly analogous
to rotating-anode sources in comparison with modern synchrotrons).

We have made considerable progress on the construction of a user
facility, Beamline 6.0.1, which will fill a critical need for the
growing ultrafast x-ray research community \[12\]. It will also serve as
a stepping stone for developing femtosecond techniques in advance of the
LCLS x-ray laser at the Stanford Linear Accelerator Center. An
in-vacuum, permanent-magnet undulator/wiggler will radiate both soft and
hard x-rays from 120 eV to 10 keV. The device has 50 periods with a
period of 30 mm and a peak magnetic field of 1.5 T. There will be two
branch lines, one with a variable-line-space grating spectrograph and
the other with a Ge (111) or Si (111) crystal monochromator. On the soft
x-ray branch, a streak camera will serve as the detector for
measurements on picosecond time scales. The ultrafast facility will make
use of an already installed wiggler (which now serves a
protein-crystallography beamline) for generating femtosecond x‑rays via
laser-modulation (slicing) of the stored electron beam. A 40-kHz
femtosecond laser system will be located at the end of the beamline and
will serve the dual purposes of providing laser pulses for slicing the
synchrotron beam and providing tunable "pump" pulses for sample
excitation. Based on the present storage-ring parameters, we expect that
x-ray pulses of 200 fs duration will be produced.

The high brightness of an optimized third generation source not only
translates directly into high average coherent x-ray flux but the
quasi-dc nature of synchrotron radiation is essential for many
experiments. For example, the diffraction of a coherent x-ray beam from
a sample has information at the spatial scale of the wavelength and over
a lateral dimension of the coherence width. Two ways to use the
information encoded are illustrated below. The upgrade is key in
providing much higher coherent flux at the optimum energies.

Zone plate-based x-ray microscopes can now achieve spatial resolutions
down to 18 nm at soft x-ray energies, and with improvements in
fabrication, some further progress can be expected. However, for the
imaging of three-dimensional objects, the thickness of the object places
severe restrictions on resolution because the depth of field scales as
the square of the resolution. For many applications, such as cellular
biology, materials engineering, in-situ study of materials in reactive
conditions, and nanotechnology, there is a pressing need to find a
technique that can look at thick objects at nanometer resolution. It has
recently been found that coherent diffraction patterns can be
reconstructed back into real space without prior knowledge of phase
information. The key is that the transform of a non-periodic object is
continuous in Fourier space and can be "oversampled." Electron-density
positivity and the sample boundary are then sufficient constraints for
convergence on a unique phase set and hence an image \[12, 13\]. We now
have the prospect of being able to image thick objects at nanometer
resolution in liquids or under reaction conditions. This capability will
give us a revolutionary new tool.

The interplay between spin, charge, lattice, and orbital degrees of
freedom produces very complex phase diagrams and nanoscale phase
behaviors in transition metal oxides. These microphases are thought to
play a key role in the properties of high-temperature superconductivity
in the cuprates and colossal magnetoresistance (CMR) in the manganites.
Again, these length scales map directly to soft x-ray probe wavelengths.
Soft x-ray coherent x-ray scattering offers important advantages, such
as high coherent flux, excellent chemical contrast, an adequate
scattering wave vector to probe nanoscale features, and access to core
levels of interest, such as oxygen and the transition metals. These
advantages should enable a much more complete characterization of these
materials, including their response to external control parameters, such
as field, temperature, and current, as well as their related dynamical
properties.

## Increased Brightness with Top Off and Advanced Undulators

At present, the ALS is operated in a mode where beam is injected three
times daily to 400 mA. In the eight hours between fills, the beam decays
to 200 mA with a time-averaged current of about 250 mA. Machine
performance of the ALS is lifetime limited. While substantial
improvements in brightness and current have always been technically
feasible, they incur the penalty of a much reduced lifetime, an option
totally unacceptable to our users. In top-off mode, injection would be
quasi-continuous, so that the lifetime impediment is less important. In
addition, because of the nearly constant current in the storage ring,
beamline optics would not suffer the large thermal fluctuations
associated with large changes in storage-ring current. These greatly
reduced thermal fluctuations of beamline optics would result in enhanced
photon position stability at all ALS beamlines.

It is also possible to increase the current in the machine to 500 mA
(Figure 1.2-1). In terms of raw flux, the combination of top-off and
increased current would therefore double our capacity in a very cost
effective way. More important than capacity, however, is enhanced
capability. The proposed upgrades will enable the newer and more
revolutionary experiments briefly outlined above.

![](media/image2.wmf){width="6.090972222222222in"
height="2.827777777777778in"}

[]{#__RefHeading___Toc91568021 .anchor}Figure 1.2‑1: Parameters of
top-off injection after the upgrade with reduced vertical emittance.

+---------------------------------+-----------------+-----------------+
| Parameter                       | Present         | Future          |
+---------------------------------+-----------------+-----------------+
| > Time Average Current (mA)     | 250             | 500             |
+---------------------------------+-----------------+-----------------+
| > Veritcal Emittance (nm•rad)   | 0.15            | 0.03            |
+---------------------------------+-----------------+-----------------+
| > Vertical Beta Function (m)    | 3.6             | 2.25            |
+---------------------------------+-----------------+-----------------+
| > Vertical Magnetic Gap (mm)    | 14              | 5               |
+---------------------------------+-----------------+-----------------+

[]{#__RefHeading___Toc91568091 .anchor}Table 1.2‑1: Comparison of
Present and Future Storage-Ring Parameters

The other half of the enhanced-brightness strategy is the insertion
device. At present, the "workhorse" at the ALS is a 4.45-m-long,
linearly polarizing undulator. The ALS has five of these insertion
devices with periods of 5, 8, and 10 cm that were designed and installed
about a decade ago. Each of these devices require one full storage ring
straight section. With subsequent significant advances in undulator
technology, the currently favored design is the 2-meter elliptically
polarizing undulator (EPU). Of these, we have two installed, one under
construction, and one proposed. Together with one wiggler, these
undulators fill nearly all available ALS straight sections.

However, insertion-device technology continues to advance, with
small-gap, short-period, in-vacuum undulators and superconducting
undulators emerging as the insertion devices of choice. So, in addition
to top-off operation with higher average current, further brightness
improvements can be realized in the core soft x-ray region by reducing
the vertical emittance and beta function of the storage ring, which
allow us to install such small gap, permanent-magnet or superconducting
insertion devices.

In Table 1.2-2 and Figure 1.2-2, we compare the brightness of the old
workhorse with the present storage ring parameters to four new small-gap
devices with the upgraded ring parameters shown in Table 1.2-1.

+----------+---------------+--------------+---------------+----------+
| Photon   | Present       | Future       | ID length,    | Imp      |
| Energy   | Brightness    | Brightness   | period,       | rovement |
|          |               |              | technology    |          |
+----------+---------------+--------------+---------------+----------+
| 500 eV   | 5.70×10^18^   | 2.04×10^19^\ | short, 30 mm, | 3.58\    |
|          |               | 6.93×10^19^  | IVU           | 12.2     |
|          |               |              |               |          |
|          |               |              | long, 30 mm,  |          |
|          |               |              | IVU           |          |
+----------+---------------+--------------+---------------+----------+
| 1000 eV  | 3.49×10^18^   | 1.88×10^19^\ | short, 30 mm, | 5.39\    |
|          |               | 4.29×10^19^\ | IVU           | 12.3\    |
|          |               | 5.83×10^19^\ |               | 16.7\    |
|          |               | 2.02×10^20^  | long, 30 mm,  | 57.9     |
|          |               |              | IVU           |          |
|          |               |              |               |          |
|          |               |              | short, 14.5   |          |
|          |               |              | mm, SCU       |          |
|          |               |              |               |          |
|          |               |              | long, 14.5    |          |
|          |               |              | mm, SCU       |          |
+----------+---------------+--------------+---------------+----------+
| 2000 eV  | 6.07×10^17^   | 3.71×10^19^\ | short, 14.5   | 61.1\    |
|          |               | 1.25×10^20^  | mm, SCU       | 206      |
|          |               |              |               |          |
|          |               |              | long, 14.5    |          |
|          |               |              | mm, SCU       |          |
+----------+---------------+--------------+---------------+----------+
| 4000 eV  | not           | 2.35×10^19^\ | short, 14.5   | ---\     |
|          | accessible    | 4.81×10^19^  | mm, SCU       | ---      |
|          | with          |              |               |          |
|          | undulators    |              | long, 14.5    |          |
|          |               |              | mm, SCU       |          |
+----------+---------------+--------------+---------------+----------+

[]{#__RefHeading___Toc91568092 .anchor}Table 1.2‑2: Comparison of
Present and Future Brightness (photons/sec/0.01%bw /mm^2^/mrad^2^)

The new devices all have a vacuum gap of 5 mm, in contrast to the 9 mm
of the older undulators. The first two are 30-mm-period in-vacuum
devices of lengths 4.3 m (long) and 1.8 m (short), respectively. These
two devices could be constructed with hybrid permanent magnets \[14,
15\]. The second two are 14.5-mm-period superconducting devices of
lengths 4.3 m (long) and 1.5 m (short), respectively \[16, 17\].

![](media/image3.png){width="3.111111111111111in"
height="1.98125in"}![](media/image4.png){width="3.170138888888889in"
height="1.9583333333333333in"}

[]{#__RefHeading___Toc91568022 .anchor}Figure 1.2‑2: Brightness
comparison of new ALS insertion devices to current insertion devices.

We see that there are one to two orders of magnitude improvement in
brightness obtainable in the soft x-ray range. In reducing the vertical
emittance after the upgrade, we also reduce the wavelength at which the
undulators become diffraction limited to 0.57 nm, i.e., the ALS will be
diffraction limited in the vertical direction throughout the whole of
the soft x-ray energy range. It should also be noted that the proposed
upgrades extend the high-energy range of the undulator radiation, which
is currently limited at 2000 eV.

## More Beamlines to Exploit the Brightness

The ALS, unlike the larger x-ray machines, has a severely limited number
of straight sections. This has meant that several world-class programs,
which would normally command one or more insertion devices, have
multiple end stations sharing a single beamline. It would be preferable
to design optical systems fully optimized to the type of science on each
beamline.

Consequently, an important aspect of the later stages of the upgrade
(beyond the scope of this CDR) is to replace some full-length, linearly
polarized undulators with chicaned straights containing two shorter,
more advanced devices. With the increased flux and brightness available,
each of these devices will perform far better than the current devices,
but at the same time allow simultaneous operation of two fully
optimized, independent, application-specific beamlines.

Our plan is to replace five workhorse insertion devices with nine newer
more advanced insertion devices plus four new beamlines that are
responsive to the scientific drivers, such as those discussed above
(Figure 1.3-3). A strategic planning process involving the full
complement of ALS management, scientific staff, user community, and
advisory bodies has been under way with the aim of identifying the
scientific areas that would benefit from such independent beamlines and
the types of beamlines needed to serve them.

![](media/image5.png){width="6.493055555555555in"
height="4.157638888888889in"}

[]{#__RefHeading___Toc91568023 .anchor}Figure 1.3‑3: Beamlines at the
ALS. In the upgrade, the five "workhorse" 4.45-m-long U5, U8, and U10
undulators would be replaced with nine shorter, small-gap devices with
higher brightness in an orderly, phased manner to minimize disruption of
the experimental program.

## Advantages to the user programs

Continual topping-off by intermittent injection of small increments to
the beam current in the storage ring will appear to many ALS users as an
operational mode at constant current. For these users, the decay of the
stored beam will become invisible. They will operate continuously with
constant photon flux. The planned value of the current in top-off mode
is 500mA. This is an increase of about a factor of two in the
time-averaged flux for all experiments.

Continuous operation avoids the breaks in data taking necessary when the
storage ring is refilled. A common experience of ALS users under pre
top-off conditions is that low-rate data-taking under a particular set
of conditions does not complete before the scheduled fill. Requests are
often made to delay the fill, usually granted, but not by more than
about ten minutes. This inconvenience will be eliminated.

With constant thermal loading of beam line components, there will no
longer be a risk of thermally driven variations of mirror alignment,
which can lead to variations of the photon flux at an experiment. The
surface of an optic in an intense x-ray beam develops a thermal bump. To
first order this resembles a change in the radius of the optical surface
and affects the optical scheme like a change in the focal length of the
optic. After top-off, these effects are constant on bend-magnet beam
lines and can be compensated. Many of these first bend-magnet mirrors
are bent, so the bending can be adjusted to remove most of the thermal
effects. (Undulator beam lines must still be designed for variable
thermal loading, because of the variability of the undulator gap.)

With top-off, there is no longer a strong requirement to maximize the
lifetime of the stored beam. And there are three benefits to be
exploited. First, the vertical emittance coupling can be reduced, to
increase the vertical source brightness. Brightness limited experiments
can enjoy higher count rates. Second, deliberate bunch lengthening may
not be necessary, so that the natural bunch length could be recovered.
This means that time resolved experiments requiring time resolution of
the order of tens of picoseconds can exploit the ALS time structure.
Faster experiments involving time resolved detectors or laser slicing
can exploit the increased peak current within the shortened bunch.
Third, the minimum gap of the undulators can be reduced. This will
require replacement of the vacuum chamber for our existing undulators.
Sector 6 will have a new in-vacuum undulator designed for this smaller
minimum gap. The low energy limit is extended for all small-gap
undulators, so that those users limited by the lowest energy of an
undulator can gain access to a larger operational range. The extended
limit allows greater freedom to optimize the period length of future
devices.

# Overall Scope of Project, Introduction of Subproject Parts

In this section we discuss the scope of the project and introduce the
subproject parts. The scope of the top-off requires upgrading the
injection system to full energy and injecting continuously with the
shutters opened. Beyond that there are several additional components
that make up the scope. The overall scope of the top-off upgrade is
listed below:

-   Upgrade injector to enable full energy injection, including
    necessary modifications to controls and timing.

-   Where necessary for operational reliability (with the higher
    requirements in top-off), improve diagnostics and other existing
    systems.

-   Install radiation safety system and conduct studies necessary for
    injection with shutters open.

    -   Acquire DOE approval for necessary Final Safety Analysis
        Document (FSAD) changes.

-   Minimize injection transients to reasonable levels.

    -   Provide user gating signal.

-   Migrate to higher current (400 à 500 mA) operation with smaller
    vertical beamsizes (150 à 30 pm rad emittance).

-   Enable bunch cleaning in booster to make top-off compatible with two
    bunch operation.

-   Transition to Top-off with minimal negative impact to users

    -   Upgrade in a typical annual shutdown and commissioning period
        (\<2 months)

    -   Minimize the initial teething period

-   Ensure that all subsystems within this project are upgraded in a
    safe manner, protecting the workers, the public, and the
    environment.

Because top-off is critical to upgrading the ALS, it is desirable to
complete the upgrade as soon as possible. If we receive the funding in
time we plan to go to upgrade to full energy injection by Mid 2006.
Subsequently we would transition to top-off injection and commission the
bunch cleaning. The total cost of the project is 4.85 M\$. To achieve
this schedule requires receiving 2.4 M\$ by March 2005 and the remaining
funds at the beginning of FY06.

In order to discuss the scope of the project it is useful to first
describe our present mode of operation.

## Present injection mode

![](media/image6.jpeg){width="5.659722222222222in"
height="6.086805555555555in"}

[]{#__RefHeading___Toc91568024 .anchor}Figure 2.1‑4: Layout of our
present injection system

Our present injection system is shown in Figure 2.1-4. It consists of a
120 kV thermionic gun followed by a 50 MeV linac, and a 0.05 to 1.5 GeV
Booster. The gun can extract 1 to more than 10 bunches of electrons
spaced 8 ns apart. The electron bunch length is compressed before
entering the linac where the electrons are further accelerated up to 50
MeV. Next the bunches pass from the linac to the Booster through the
Linac-to-Booster (LTB) transfer line where they are injected into the
Booster synchrotron. A Booster injection kicker is excited when the
electrons enter the booster ring and causes the electrons to be injected
on-axis. The injection kicker flat top is long enough to allow more than
10 bunches (spaced 8 ns apart) to be injected into the Booster.

![](media/image7.jpeg){width="4.579861111111111in" height="4.8in"}

[]{#__RefHeading___Toc91568025 .anchor}Figure 2.1‑5: Booster ramping
cycle.

The lattice of the Booster is a FODO structure consisting of 24 dipoles,
32 quadrupoles, and 20 sextupoles. The Booster lattice is 4-fold
symmetric with 4 straight sections -- one for injection, one for
extraction, one for RF, and the other for diagnostics (such as the DCCT,
a direct current current transformer). The Booster ramps the electron
energy from 50 MeV to 1.5 GeV and the electrons are extracted. The
Booster can cycle at 1 Hz between 50 MeV and 1.5 GeV. The Booster bend
magnet ramping cycle is shown in Figure 2.1-5.

The Booster extraction consists of 3 bump magnets to move the stored
beam towards the septa magnets, a fast (single-turn) extraction kicker,
and thin and thick septa magnets where the electrons enter the
Booster-to-Storage Ring (BTS) transfer line. The electrons then pass
through the BTS line to the storage ring where they are injected into
the storage ring

The electrons are injected into the storage ring in straight 1. In that
straight section there are four bump magnets and a thin and thick septum
magnet. The electrons passing down the BTS magnets enter the thick and
thin septa magnets while at the same time the electrons in the storage
ring are bumped toward the septa magnets by the 4 fast bump magnets.
After entering the ring the injected electrons oscillate radially about
the stored electron beam. This oscillation is slowly damped (\~15 ms)
due to radiation damping. After one second a fresh bunch train of
electrons can be injected. Once the storage ring is filled, the storage
ring is ramped up in energy from 1.5 GeV to 1.9 GeV.

The storage ring is 196 m long and with a 500 MHz RF system it is
possible to fill up to 328 bunches. There are two basic bunch fill
patterns -- multibunch and 2 bunch. In multibunch pattern a long train
of bunches is filled (usually 276 bunches) followed by a gap. Sometimes
in multibunch fill mode one bucket in the gap is filled -- the so called
camshaft bunch. The bunch current is 400 mA at the top of the fill with
10 mA in the camshaft and the remainder of the current evenly
distributed between the other 276 bunches.

In 2-bunch fill mode two bunches on either side of the storage ring are
filled (up to 30 mA / bunch). This fill pattern is used for experiments
requiring a long gap between pulses for timing experiments. The current
in the gap needs to be much smaller than that of the filled bunches (\<
0.01%). The ratio of the current of the non-targeted to the targeted
bunches is called the bunch purity. Non-targeted bunches are filled
because some of the non-targeted bunches in the injector also contain
current. So after injection and bringing the ring up to full energy,
beam is ejected out of the non-targeted bunches through resonant
excitation. After the non-targeted bunches are cleaned the beam is given
to users.

In 2 bunch mode, the time between fills is 2 hours rather than 8 hours
due to the shorter lifetimes. The lifetime in the ALS is primarily
determined by intrabeam scattering and is shorter in 2-bunch mode
because of the higher beam currents per bunch.

At present the injector is run in either in single bunch injection mode
or with a bunch train of 3 to 4 bunches. When the injector is well tuned
up it will inject more than 1.5 mA in 4 bunches into the storage ring
every second.

At present the lifetime is increased to acceptable levels by decreasing
the electron bunch density. The vertical beam size is increased by
introducing some vertical dispersion with skew quadrupoles. The
longitudinal beam size is doubled through the use of a third harmonic RF
system.

## Parameters and operation with Top-off

With top-off operation we plan to double the time average current by
keeping the current constant at 500 mA. In addition we plan to reduce
the vertical emittance from the present value of 150 pm-rad to 30
pm-rad. Figure 1.2-1 shows the planned parameters after top-off
operation. During special accelerator physics shifts, the ALS has run
with vertical emittances as low as 5 pm-rad Error: Reference source not
found\]. So 30 pm-rad are easily achievable in normal user operation.

Because of the higher currents and lower vertical beam sizes the
lifetime will become shorter. With our parameters, the lifetime at 500
mA will be 3 hours as opposed to 8 hours at 400 mA with the present
parameters. In the intrabeam (so-called Touschek) dominated regime, the
time between fills *∆T* is related to the drop in current *∆I* from the
initial current, *I~i~* , to the final current, *I~f~*, by the relation

![](media/image8.wmf)

where *τ~i~* is the beam lifetime at the top of the fill. For present
operation in 8 hours the current decays by 200 mA. In top-off operation
the beam will decay by 1.5 mA in 32 seconds.

These parameters are the baseline parameters. Note that one can adjust
them based on the needs of the users. It will also be possible to run
with different sets of operating parameters during different running
periods.

During top-off we assume that we can inject 1.5 mA per pulse. Presently
it is possible to achieve 1.5 mA per pulse in 4 bunches. This is done
with insertion device gaps opened and with a minimum vacuum chamber
aperture of 8.9 mm full gap. With top-off we need to inject with
insertion devices closed. Also the minimum vacuum chamber aperture will
be as small as 5 mm. Our preliminary machine studies have shown a 40%
reduction in injection efficiency with IDs closed and a vertical scraper
with a 5 mm aperture. The plan for Top-off is to inject with a longer
train, up to 10 bunches, and to improve the injection efficiency.
Studies of the longer bunch trains and to improve the injection
efficiency will be performed as part of the precommissioning.

+-----------------------------------+-----------------------------------+
| **Present Operation**             | **After Top-Off**                 |
|                                   |                                   |
| -   **Injection at 1.5 GeV and    | -   **Full energy injection (1.9  |
|     then ramp**                   |     GeV)**                        |
|                                   |                                   |
| ```{=html}                        | ```{=html}                        |
| <!-- -->                          | <!-- -->                          |
| ```                               | ```                               |
| -   **Inject with insertion       | -   **Inject with insertion       |
|     devices open**                |     devices closed**              |
|                                   |                                   |
| ```{=html}                        | ```{=html}                        |
| <!-- -->                          | <!-- -->                          |
| ```                               | ```                               |
| -   **Average beam current is 250 | -   **Average beam current is 500 |
|     mA**                          |     mA**                          |
|                                   |                                   |
| ```{=html}                        | ```{=html}                        |
| <!-- -->                          | <!-- -->                          |
| ```                               | ```                               |
| -   **Vertical emittance is 150   | -   **Vertical emittance is 30 pm |
|     pm rad**                      |     rad**                         |
|                                   |                                   |
| ```{=html}                        | ```{=html}                        |
| <!-- -->                          | <!-- -->                          |
| ```                               | ```                               |
| -   **Lifetime is 8 hours at 400  | -   **Lifetime is about 3 hours   |
|     mA**                          |     at 500 mA**                   |
|                                   |                                   |
| ```{=html}                        | ```{=html}                        |
| <!-- -->                          | <!-- -->                          |
| ```                               | ```                               |
| -   **Injection period every 2 to | -   **Injection period about      |
|     8 hours**                     |     every 30 seconds**            |
|                                   |                                   |
|     -   **1 Hz injection for 4    |     -   **1 pulse**               |
|         minutes**                 |                                   |
|                                   |         -   **From 498.5 to 500   |
|         -   **From 200 to 400     |             mA**                  |
|             mA**                  |                                   |
|                                   | -   **Photon shutters remain open |
| -   **Photon shutters are closed  |     during injection**            |
|     during injection**            |                                   |
|                                   | -   **Parasitic Bunches cleaned   |
| ```{=html}                        |     in the booster**              |
| <!-- -->                          |                                   |
| ```                               |                                   |
| -   **Parasitic bunches cleaned   |                                   |
|     in the storage ring**         |                                   |
+-----------------------------------+-----------------------------------+

[]{#__RefHeading___Toc91568093 .anchor}Table 2.2‑3: Difference between
present operation and operation after the top-off upgrade

Bunch cleaning in the storage ring is not an ideal solution with top-off
because the cleaning process perturbs the stored beam. The plan is to
clean the bunches in the Booster and cleanly inject into the storage
ring. Injecting clean bunches is essential for using top-off with 2
bunch operation. This has been achieved at the APS, ESRF, and is in
routine operation at Spring-8.

Table 2.2-3 shows the difference between present operation and operation
after the top-off upgrade. There are several major changes from present
operation to operation with top-off. A major issue that is being
addressed is radiation safety with top-off. With top-off operation we
will need to inject with the personnel safety shutters opened. It is
important that when we inject with the personnel safety shutters opened
that we prevent "freshly injected" electrons from passing down the beam
line. In addition we need to mitigate the increased radiation levels due
to injected electrons striking the storage ring vacuum chamber near the
beamlines, the increase in normal stored losses, and the increase in
levels due to RF trips. Finally, it is important to minimize the
radiation levels near radiation sensitive equipment such as permanent
magnet insertion devices, electronics equipment, etc. The plan for
addressing these issues is described in section 3.2.

A very important aspect of the upgrade is to ensure that the transition
to top-off operation is smooth with minimal impact to the present users.
Therefore we plan to use our 1 and 2-day monthly shutdowns plus typical
annual shutdowns of \< 2 months for the installation of the components
for the project. In addition we need to ensure that we minimize the
teething period after the installations.

## Introduction of the Subparts of the CDR

In Section 3 we provide a detailed description of the various parts of
the top-off upgrade project. In Section 3.1 we discuss the user
requirements including operational tests performed to evaluate any
negative impact from injection transients on the different types of user
experimental techniques. In Section 3.2 we discuss radiation safety
issues. Section 3.3 presents accelerator physics studies done in
preparation of top-off as well as some precommissioning studies. In
Section 3.4 we discuss the injector reliability -- what is the present
reliability of the injector and what are the issues for top-off. In
Section 3.5 we discuss the necessary upgrades to the pulsed magnets. A
lot of work was done this past year to determine what was necessary to
upgrade. Fortunately most of pulsed magnets are fine with small
modifications. In Section 3.6 the upgrades of the DC and slow ramped
magnets are discussed. The magnets themselves are capable of 1.9 GeV
operation. The power supplies need to be upgraded. In Section 3.7 we
discuss the upgrades needed for the timing system for the injector as
well as the user gating system. The user gating system will provide a
warning to users that an injection pulse is coming so that they may gate
out that time. The Booster RF system is discussed in Section 3.8.
Upgrading the RF windows and amplifier/transmitter is necessary and is
one of the larger systems that need to be upgraded for the project.
Diagnostics are discussed in Section 3.9. Upgrades in diagnostics are
necessary for top-off as well as to perform bunch cleaning in the
booster. Computer control system upgrades are discussed for the various
systems in Section 3.10. In Section 3.11 we discuss the present
utilities. Because we do not require 1 Hz injection (we plan to run with
1/3 Hz injection), it is not necessary to upgrade the utilities.
Finally, in Section 4 the cost, schedule, and installation of the
upgrade project is discussed.

# Detailed Description of all Parts of the Top-off Upgrade

## User requirements

Figure 1.2-1 shows the pre top-off and the proposed post top-off current
profile in the storage ring. Pre top-off, the shutters are closed, the
undulators are opened and the storage ring is refilled about every 8
hours. Post top-off, the time between injection pulses is ∆t and the
current is increased each time by δi. The injection transient duration
is δt. Likely post top-off values are tabulated here.

  -------- -------- -------- ------------ -------- -------- -------- --------
  δi       ∆t       δt       ε~v~         σ~h~     σ~v~     σ\`~h~   σ\`~v~

  1.5 mA   32.0 s   50 ms    30x10^-12^ m 298 μm   8 μm     22 μrad  3 μrad
                             rad                                     
  -------- -------- -------- ------------ -------- -------- -------- --------

[]{#__RefHeading___Toc91568094 .anchor}Table 3.1‑4: Operational
parameters chosen as goal for the ALS top-off upgrade.

Table 3.1-4 shows an intermediate coupling situation where the vertical
brightness is increased up to the point where the vertical source RMS
size shrinks to 8μm in the center of the straight section. This seems a
reasonable place to operate, because smaller sources impose a figure
requirement on the first optic that can be very difficult to maintain.
For example, a sagittally focusing, horizontally deflecting first mirror
on a soft x-ray undulator beam line typically deflects through 3
degrees. Such a mirror would be internally cooled with carefully
engineered channels carrying water perhaps 1.5mm below the optical
surface. It would be manufactured out of copper or silicon. Located
inside the shield wall, its thermal deformation at full current with the
undulator closed might give rise to an rms sagittal slope error,
weighted by the illumination intensity of the useful radiation, of about
10 micoradians. This deformation depends on the undulator gap and must
blur the source by a negligible amount. That would be about 4μm in this
example.

[]{#__RefHeading___Toc91568026 .anchor}Figure 3.1‑6: Heating induced
focusing error on sagittally focusing mirror.

The time between injection is set by the need to inject 1.5mA each time.
This is the limit from a single booster pulse. Polling users during the
operational tests revealed a desire for widely spaced injections with a
short transient. For those experiments requiring an inhibit-gate, 30
seconds between injections seemed reasonable.

### Operational Tests

Operational tests suggest that there will be some users who will notice
the effects of the top-off injection process, because of the sensitivity
of their experiment to the position of the electron beam. Transient
perturbations of the closed orbit around the ring are likely at the time
of top-off injection. These orbit perturbations can cause a transient
change in the flux delivered into those experiments that make use of an
image of the source on an aperture. A gating signal will be provided,
which will mark the timing of the top-off injection. Those experiments
sensitive to the injection transients must find some way to inhibit
data-taking during injection.

This past year a number of measurements were done to evaluate the impact
of the injection process on the users. During three accelerator physics
shifts, experiments were performed with representatives from various
beam lines - 1.4, 4.0, 5.3.2, 6.3.2, 7.0, 7.3, 8.3.1, 10.0, 10.3.2,
11.0.2, and 12.0. During these experiments, data was taken with the
injection elements turned on and compared with the case where the
injection elements were not turned on. These results were presented at
several meetings including a spring UEC meeting. The results are
summarized in light source note LSBL-709.

In top-off, the beam line shutters remain open during injection and the
injection process itself is not completely transparent to all users. In
particular, the injection magnets perturb the stored beam during
injection. At present there is a fast oscillation caused by non-closure
of the pulsed injection bump magnets, as well as a slower closed orbit
distortion caused by decaying eddy currents in the main septum magnet.

![](media/image9.png){width="4.748425196850394in"
height="3.844488188976378in"}

[]{#__RefHeading___Toc91568027 .anchor}Figure 3.1‑7: Fast (vertical and
horizontal) oscillation of the beam, due to mismatch of the bump
magnets. This lasts less than 1 ms.

![](media/image10.png){width="4.698031496062992in"
height="3.802755905511811in"}

[]{#__RefHeading___Toc91568028 .anchor}Figure 3.1‑8: Slower (horizontal)
closed orbit distortion, due to the septum magnet eddy currents, that
lasts about 0.1 s.

The results of these studies were that most of the experiments did not
see the injection transients. Scanning instruments with short
integration times were most affected. By far the most sensitive
technique was STXM, with transient intensity fluctuations from 5% to
40%, depending on whether the septum magnet was pulsing. The infra-red
beam line could also detect these injection transients. Some
spectroscopy counting experiments (for example at beam line 4.0) saw the
effect of the pulsed septum magnet, but not the fast bumps. We are
currently in the process of reducing the impact of the septum on the
beam transients.

![](media/image11.jpeg){width="3.4916666666666667in" height="3.75in"}

[]{#__RefHeading___Toc91568029 .anchor}Figure 3.1‑9: Injection
transients causing an intensity fluctuation during a horizontal line
scan in STXM at beam line 11.0.2 (second test 7 Dec 2003). Septum magnet
turned off. One horizontal line scan takes 60 ms.

Gating seems to be a requirement for these sensitive experiments. For
example, in STXM the microscope scans a horizontal line of the image and
the vertical image position is stepped one pixel while the horizontal
scanner resets for the next horizontal line. The inhibit gate will
inform the microscope computer that an injection has occurred and the
next vertical step will be inhibited. The next horizontal line scan will
be a repeat and the corrupted line will be overwritten.

## Radiation Safety

### Top-off Radiation Issues/challenges

Gamma radiation or neutrons are generated in the ALS when electrons
collide with vacuum chamber components or gas particles. The manner with
which electrons are lost can be divided into three categories.

1.  Injected electrons not being captured in the storage ring.

2.  Slow loss of electrons from the stored beam - mostly due to
    intrabeam scattering.

3.  Loss of the whole stored beam when the RF is suddenly turned off --
    RF trip.

The scope of the ALS top-off upgrade has several changes in operation
that will have an impact on the radiation levels.

1.  Injection will take place with the personnel safety shutters opened
    and the insertion device gaps closed.

2.  The average current will be increased by a factor of 2.

3.  The beam size will be decreased by a factor of 2 to 3.

The first is a fundamental change that is unique to top-off. All three
of these changes will increase the amount of electron beam loss in the
ALS. In addition to personnel safety issues, higher radiation losses
near permanent magnet or hybrid insertion devices result in a more rapid
rate of deterioration of those insertion devices.

In this section we will describe our plan to mitigate the radiation
issues resulting from the top-off upgrade. We first describe our current
radiation practices and results. Next we will discuss the issues of
top-off and our plan for dealing with each of them. Finally we will
present our future plan and our preparations for a safety review to
modify the ALS safety envelope.

### Current Radiation Practices and Results

#### Radiation Monitoring Systems

Presently there are a variety of passive and active monitoring systems
located around the ALS. The locations of these monitors are shown in
Figure 3.2-10. There are two types of active systems that are constantly
monitoring the radiation levels:

-   12 interlocked neutron/gamma monitors

-   \~25 beamline 1st optics gamma monitors

The 25 beamline optics monitors are not interlocked. They alarm in the
control room if the level reaches or exceeds 5 mrem/hr.

There are three types of passive monitors.

-   \~50 in-close dosimeters

-   12 peripheral dosimeters

-   \~50 badged staff

The first two are measuring radiation levels around the clock for the
entire year. The ALS dosimetry policy requires people to wear dosimetry
if they expect to spend more than 10% of their time inside the area
defined by the outer storage ring shield walls. This typically excludes
users from the requirement to wear dosimeters.

![](media/image12.png){width="5.073611111111111in"
height="6.0159722222222225in"}

[]{#__RefHeading___Toc91568030 .anchor}Figure 3.2‑10: Locations of
Radiation Monitors at the ALS.

![](media/image13.jpeg){width="2.5in" height="2.15625in"}
![](media/image14.jpeg){width="2.5444444444444443in" height="2.1625in"}

[]{#__RefHeading___Toc91568031 .anchor}Figure 3.2‑11: Active Radiation
Monitors: Interlocked Neutron/Gamma Monitors (left) and Optics Gamma
Monitors (right).

![](media/image15.jpeg){width="2.875in" height="2.4368055555555554in"}
![](media/image16.jpeg){width="2.625in" height="2.4451388888888888in"}

[]{#__RefHeading___Toc91568032 .anchor}Figure 3.2‑12: Passive Radiation
Monitors: In-close dosimeters (left) and Peripheral dosimeters (right).

The in-close dosimeters are located throughout the experimental floor.
The majority of the dosimeters are positioned close to the shield wall
near first optics tanks where we expect the highest scatter from gas
bremsstrahlung. Some are also located at the end of beamlines where
users spend the majority of their time. The in-close dosimeters are read
every 4-6 weeks

![](media/image17.wmf){width="4.877083333333333in"
height="5.8805555555555555in"}

[]{#__RefHeading___Toc91568095 .anchor}Table 3.2‑5: A January 2004
summary report of the in-close gamma and neutron monitors.

and the neutron monitors are read every 3-4 months. In Table 3.2-5 a
summary report is shown for January 2004. Results have been corrected
for background. This report represents a typical average period and
demonstrates the low stray radiation levels on the ALS experimental
floor.

There have been no readings above background in the peripheral
neutron/gamma monitors in more than 10 years of operation of the
machine. There have been no readings above background of the 50 badged
permanent staff directly related to ALS operations.

The difference between annual doses as measured by the in-close
dosimeters and the combined results of both the peripheral dosimeters as
well as staff dosimeters indicates the conservative placement of the
in-close dosimeters as well as an indication of the personnel occupancy
factor -- the fraction of a year a person actually spends on the
experimental floor, particularly in the region of ID first optics tanks.
Our approach has been to provide passive monitoring around the locations
of highest scattered radiation levels and when the levels exceed an
annual dose of approximately a few hundred mrem, based on continuous (no
occupancy factor) monitoring, to reduce the levels by providing local
shielding around the source of scattered radiation.

Based upon the 10 years of results for the peripheral dosimeters and
personnel dosimeters this approach seems sufficient for current
operations. With the increased losses projected for top-off operations,
a different approach is required -- one which attempts to control or
localize electron beam losses in the storage ring and then provides the
necessary local shielding inside the storage ring shield walls in order
to reduce potential radiation levels on the experimental floor and
minimizes the impact of additional shielding that otherwise might be
required on beamlines.

### Top-off Radiation Issues/Challenges

#### Preventing "freshly" injected electrons passing down beam line

In our present operation the beam line personnel safety shutters (PSS)
are closed when beam is injected. With top-off operation it is necessary
to inject electrons with the personnel safety shutters opened. If
injected electrons pass down the beam pipe they will strike the first
optic in the beam line. If the full charge of a freshly injected bunch
strikes a first optic the radiation dose can be unacceptably high.
Figure 3.2-13 shows a calculation of the unshielded dose equivalent at
30 cm from one injected pulse of electrons carrying 1 nC of charge and
striking a high Z material. This charge of 1 nC is roughly the amount of
charge we anticipate injecting in a single shot into the storage ring.
At large angles the dose equivalent is about 20 mRem however in the
forward direction the dose equivalent can be 10-100 Rem. This is clearly
an unacceptable accident condition that cannot be allowed to occur.
Therefore it is critical that we demonstrate, or provide passive
protection to insure that it is impossible to inject electrons down any
beam line. Preventing electrons from being injected down the beam line
is a condition that has been addressed at other facilities doing top-off
such as the APS \[19\], SLS \[20\], and Spring-8 \[21\]. We have adopted
a similar strategy to those facilities.

![](media/image18.png){width="4.751388888888889in"
height="3.140972222222222in"}

[]{#__RefHeading___Toc91568033 .anchor}Figure 3.2‑13: Passive Dose
equivalent at 30 cm of one injected pulse of electrons carrying 1 nC of
charge striking a high Z material.

One can easily conceive of a scenario where injected electrons can pass
down a beam pipe. Any of the 36 bend magnets could be shorted such that
an injected e- beam would be directed down the front end and into the
beam line instead of its nominal 10 degree bend in the storage ring.
Such a condition would preclude storing beam. Therefore the basis of all
our tracking studies, as has been done elsewhere, is the requirement
that there be stored beam. These studies are detailed in the following
sections.

Another scenario whereby electrons might be directed down a beam line is
the quenching of one of our Superbend dipoles. The ALS has installed
three of these superconducting dipole bend magnets. The first beam port
on a Superbend magnet is at 8 degrees. The nominal bend is 10 degrees.
If the Superbend were at 80 percent of its nominal field, the injected
electrons upon exiting the Superbend magnet would travel down the 8
degree bend magnet beam line. Simulations \[22\] have shown that a 1
percent change in the Superbend nominal field would result in the loss
of stored beam. Recent measurements indicate that the time during a
quench for the Superbend to drop to 80 percent of its nominal field is
greater than 0.5 seconds. Beam loss would occur at 1 percent drop and in
a fraction of a millisecond thereafter. The loss of stored beam could
easily trigger the radiation safety interlock system to inhibit the next
injected pulse.

In the next section the tracking studies are detailed and requirements
for preventing electrons from being injected down a beam line are
summarized.

#### Tracking Study Assumptions

Following similar approaches as used by the APS \[19\], ESRF \[24\], and
others, we track particles backwards from the point or beam line of
interest to the injection point of the storage ring. If it is determined
that particles cannot be successfully tracked from a beam line front end
to the injection point then the inverse must also be true -- that
injection into the storage ring cannot be directed down the beam line.
The condition of stored beam is assumed.

Beam line 2.1, which is currently under design, will become the closest
beam line to the storage ring injection point. Straight sections 1 and 3
will not have insertion devices as these straights are used for
injection and rf cavities. Straight 2 may some day contain an insertion
device however our current estimate is that it may prove more difficult
to inject down 2.0 than 2.1 since by definition 2.0 is the 0 degree port
and any electron beam must therefore pass through the B1 magnet with no
deflection.

![](media/image19.png){width="5.885416666666667in"
height="3.9479166666666665in"}

[]{#__RefHeading___Toc91568034 .anchor}Figure 3.2‑14: Geometry of x.1
beamline. Rays A-D mark the extremes in angle and offset that still pass
through the frontend apertures. Ray N marks the nominal center of a x.1
beamline.

  ------ ---------- ----------- ----------- ------- ---------- ----------- -----------
  Line   T(rad)     T(deg)      dT(rad)     Point   Xo(m)      dX(m)       Z(m)

  N      0.240517   13.780577   0.000000    0       0.334870   0.000000    -0.000790

  A      0.326554   18.710122   0.086037    3       0.392060   0.057190    0.000960

  B      0.242500   13.894194   0.001983    1       0.320070   -0.014800   0.000010

  C      0.236502   13.550535   -0.004015   4       0.284490   -0.050380   0.000010

  D      0.200081   11.463770   -0.040436   2       0.278820   -0.056050   0.000010
  ------ ---------- ----------- ----------- ------- ---------- ----------- -----------

[]{#__RefHeading___Toc91568096 .anchor}Table 3.2‑6: Geometry parameters
of the apertures for a x.1 beamline.

The geometry is outlined in Figure 3.2-14 and Table 3.2-6. The reference
ray is Line N. The 4 lines (A \~ D ) are defining the boundary marking
the outer boundaries of the 2.1 exit port and limited by the downstream
photon stops. With respect to Line N, the other 4 rays are in the range
of -40 mrad to 86 mrad. For conservatism we simply sample over -50 mrad
to 100 mrad. Simarly for position offsets we sample over the range -70
mm to

![](media/image20.wmf){width="6.0in" height="4.392361111111111in"}

[]{#__RefHeading___Toc91568035 .anchor}Figure 3.2‑15: Maximum distance
injected back to SR injection point.

70 mm. Particles are injected at the longitudinal location of BPM5 just
downstream of the second bending magnet (at the locations marked as 0-4
in the Figure) on Line N. Realistic physical aperatures and magnetic
field profiles are used.

#### Tracking Study Results

Tracking results are summarized in Figure 3.2-15 for injected beam
energy to stored beam energy ratios (P/P~0~) ranging from 1% to 200%. It
is clear from this plot that there is no condition for which the beam
injected at beam line 2.1 can travel completely back to the injection
point at 25 m. The results indicate that the nominal beam energy reaches
less than half way to the injection point. There is however a range of
P/P~0~ (40% to 62% and \> 125%) for which the injected beam reaches
within about 5 m of the injection point.

To demonstrate why this happens, the paths of several particles are
selected and plotted together with the physical apertures. This is shown
in Figure 3.2-16. Here it can be seen that nominal energy particles hit
the entrance to the upstream straight section while there is a solution
for extreme P/P~0~ particles to produce a trajectory through the
straight section. This indicates that the physical apertures provided by
the straight section are very effective in filtering out particles of
approximately nominal energy. The results were repeated while varying
individual quadrupoles in the storage ring by +/- 20%. The results did
not significantly change the results.

![](media/image21.wmf){width="5.998611111111111in" height="4.18125in"}

[]{#__RefHeading___Toc91568036 .anchor}Figure 3.2‑16: Trajectories of
several important particles

#### Tracking Study Conclusions

Based on these analyses, the following condition is necessary to prevent
from being inadvertently injected down a beamline:

-   There must be stored beam in the ring. We plan to use a threshold
    current of 10 mA for the interlock system, which is easy to measure
    and small enough compared to normal operation conditions in
    two-bunch operation not to cause any unnecessary injection inhibits.

As additional precaution, we plan to insure that the match between the
booster extraction energy and the storage ring beam energy is within
10%.

Horizontal collimators are being designed for installation in the
booster-to-storage ring transfer line to remove the tails of the
injected beam distributions, which due to the relatively large emittance
of the booster and the limited dynamic aperture of the storage ring
would not be captured. Future studies will include more intuitive
forward calculations as well as verifying that beam line 2.1 represents
the limiting case.

#### Stored Beam Losses

Aside from considerations for the worst case accident scenario, there
will be increased stray radiation levels due to the increased number of
electrons. Topping off the stored current every 30 seconds with 1.5 mA
yields 1440 mA /shift. Since beam current will be kept constant at 500
mA this results in 1440 mA of electrons lost per 8 hr shift. Present
operations result in a loss of approximately 200 mA. This leads to
roughly a factor of 7 increase in beam loss and hence stray radiation
levels.

Beam losses from Touschek scattering and from RF trips now are lost
mainly in the small vertical gap insertion devices at 4.0 and 11.0 with
smaller losses occurring elsewhere. Little effort has been made or has
been required to locally collimate losses due to the low stray radiation
levels. Increases in these levels by a factor of 7 or more dictates a
strategy of providing collimation and then locally shielding the
collimator(s). This section describes closed orbit distortion
simulations to determine the effectiveness of vertical collimators
placed in any of 6 available locations in one or more arc sector
chambers. These locations are commonly referred to as Jackson holes. The
locations of these are shown in Figure 3.2-17.

![](media/image22.jpeg){width="6.115972222222222in"
height="3.270138888888889in"}

[]{#__RefHeading___Toc91568037 .anchor}Figure 3.2‑17: Jackson hole
locations on arc sector

Closed orbit distortion calculations were carried out to determine the
location of beam loss as a function of vertical collimator aperture
heights assumed to be located in several Jackson holes (JH). The RF is
assumed to be turned off instantly, allowing stored beam to lose energy
via synchrotron radiation. Interaction between beam and unpowered
cavities is ignored. During tracking apertures are checked at each JH
location as well as at the entrance of each straight section. The
process is repeated for 100 random seeds.

![](media/image23.jpeg){width="6.366666666666666in"
height="3.470138888888889in"}

[]{#__RefHeading___Toc91568038 .anchor}Figure 3.2‑18: Closed orbit
distortion following rf trip.

Figure 3.2-18 shows the tracing of one injected particle with no JH
scrapers present. This demonstrates the horizontal and vertical orbit
distortion increasing with subsequent loss at the ID4 entrance,
consistent with present experience and measurements. Particles can
survive on average several hundred turns before hitting a small vertical
aperture.

Figure 3.2-19 gives a summary of beam loss for JH vertical scrapers
located at SR02 JH6 and SR03 JH1. These are located at the exit of arc
sector 2 and the beginning of arc sector 3, locations where betatron
oscillations are the largest giving more flexibility in actual
adjustment to scraper heights. This demonstrates that the proper
location and adjustment of vertical collimators/scrapers located in
existing Jackson holes can be used as an effective strategy in
localizing beam losses.

Future work will determine optimal number and location of JH scrapers to
localize beam losses from both Touschek scattering and RF trips.
Simulations and measurements will also determine the effect of JH
scraper heights on stored beam lifetime. These scrapers will be designed
so that aperatures can be changed but then locked into a position such
that they cannot be inadvertently removed from their intended function
of minimizing stray radiation levels on the experimental floor. Two sets
of collimators will be installed. By placing two collimators apart by 90
degrees horizontal phase advance, one can collimate both in displacement
and angle. With the use of those collimators, radiation levels for
permanent magnet insertion devices and due to bremsstrahlung for user
beamlines can be minimized.

![](media/image24.wmf){width="6.247222222222222in"
height="4.483333333333333in"}

[]{#__RefHeading___Toc91568039 .anchor}Figure 3.2‑19: Beam loss at SR02
JH6 and SR03 JH1 as a function of JH half gap height.

### Collimation/Scraper System

#### Horizontal Collimators in the BTS line

The purpose for these collimators is to allow to remove particles at
large horizontal amplitudes (i.e. in the tails of the beam
distribution), which due to the relatively large emittance of the
booster and the limited dynamic aperture of the storage ring would not
be captured anyhow. By placing two of those collimators apart by 90
degrees horizontal phase advance, one can collimate both in displacement
and angle. With the use of those collimators, radiation levels for
permanent magnet insertion devices and due to bremsstrahlung for user
beamlines can be minimized.

![](media/image25.jpeg){width="2.879861111111111in"
height="2.911111111111111in"}![](media/image26.jpeg){width="3.4805555555555556in"
height="2.479861111111111in"}

[]{#__RefHeading___Toc91568040 .anchor}Figure 3.2‑20: CAD drawing of the
double sided horizontal collimator for the BTS transfer line.

#### Vertical Scrapers in the Storage Ring

In addition to the collimators in the BTS line we will also install
vertical moveable collimators/scrapers in the ALS storage ring. They
will serve 3 different purposes:

1.  Localizing injection losses

2.  Localizing stored beam (lifetime) losses

3.  Localizing losses due to beam dumps (RF aborts)

In all of those cases, the particle losses in the ALS occur in the
vertical plane, either due to particle diffusion/single particle
resonances, or due to a resonant explosion of the vertical closed orbit
when the vertical tune changes close to the half integer resonance in
the case of an RF abort. The simulation investigating the effectiveness
and optimum location for these scrapers are shown in Section 3.2.3.5.
After the installation early next year, detailed beam studies will be
conducted, including injection with one beamline shutter open to fully
detail the effectiveness of the scraper system. Even though it is not
envisioned that the scrapers will be an integral part of the radiation
protection system (but rather a means to reduce steady state radiation
levels to avoid posting of radiation areas), their mechanical design is
done such that they could be easily locked in a position, which would
enable their use in a radiation protection system. Using the combination
of the collimators in the BTS line and the scrapers in the storage ring,
it is expected that steady state radiation levels close to the first
beamline optics and the deposited radiation doses in insertion devices
will not increase with top-off, but stay about the same or even get
smaller.

![](media/image27.jpeg){width="3.0479166666666666in"
height="3.8513888888888888in"}

[]{#__RefHeading___Toc91568041 .anchor}Figure 3.2‑21: A pair of vertical
scrapers installed in the so-called Jackson holes of one of the storage
ring arc vacuum chambers.

![](media/image28.jpeg){width="2.129861111111111in"
height="3.9451388888888888in"}![](media/image29.jpeg){width="2.077777777777778in"
height="3.9472222222222224in"}

[]{#__RefHeading___Toc91568042 .anchor}Figure 3.2‑22: Drive system,
cooling and inner structure of vertical scrapers.

### Radiation Monitors

The existing system of beamline radiation monitors will be upgraded with
a new (faster) readout electronics that also provides the capability to
implement an interlock system. It has not been decided, yet, whether an
interlock system is necessary. The decision will be based on injection
radiation level measurements with one beamline shutter open during the
coming year. However, all components that would be needed for a beamline
interlock system are currently included in the scope, schedule and cost
estimate of the project.

### Top Off Mode, Radiation Safety System

Currently the ALS operates in two modes. During injection we run in fill
mode. All the beamline Personal Safety Shutters (PSSs) are closed and
the BTS bend power supplies (PS) for the first two bend magnets (B1, B2)
in the transfer line between the booster and the storage ring are
enabled to be turned on. After injection the operators switch the
accelerator to stored beam mode. The BTS bend magnet PS are disabled and
the beamline PSSs are enabled to open. (Please see Figure 3.2-23)

![](media/image30.wmf)

[]{#__RefHeading___Toc91568043 .anchor}Figure 3.2‑23: Potential
operational modes and logic for transitioning between them both for the
current ALS operation and for top-off. B1 and B2 are the first two
bending magnets in the booster to storage ring (BTS) transfer line.

For the top-off mode modification we will retain fill and stored beam
modes and add top-off mode as a third operating condition. From the fill
mode the operator will be able to elect to go to one of two modes,
either stored beam mode or top-off mode.

In order to switch to top-off mode two requirements must be met.

1.  The storage ring beam current monitor interlock must be made up to a
    value yet to be determined.

2.  The injection energy must match the storage ring energy. The
    interlock circuitry will monitor and compare the currents of a BTS
    bend magnet PS with the current of the storage ring gradient PS.

Top-off mode will enable the BTS bends to operate with the beamline PSSs
open.

![](media/image31.wmf)

[]{#__RefHeading___Toc91568044 .anchor}Figure 3.2‑24: Logic of a
(potential) beam line radiation monitor interlock system.

A number of radiation monitors will be added to the beamline area of the
ALS in addition to the already existing system described earlier. All
beamline radiation monitors could be interlocked and a possible reaction
of the system to the detection of excessive radiation levels would be to

1.  Send a "Close Shutter" command to all the beamline PSSs.

2.  Generate a trigger inhibit signal to disable the booster extraction
    magnets and the storage ring injection magnets.

3.  The accelerator will revert back to fill mode.

After all the beamline PSS report back that they are closed, the trigger
inhibit signal would be turned off. The radiation monitor interlock
would have to be reset manually at the beamline the radiation monitor
resides at before resumption of top-off mode.

#### Top Off Mode, Radiation Safety System (cont)

The beam current interlock will utilize two sources for storage ring
beam current monitoring.

1.  The DCCT SR05

2.  A BPM array by summing the four buttons.

The injection energy interlock will monitor two of the BTS bend magnet
PS currents and then compare them to the SR gradient PS current ensuring
the BTS line and the storage ring energies match.

One BTS bend PS will have a transducer added for monitoring and on the
second BTS bend PS we will monitor the current signal from the PS
itself. On the gradient PS we will once again monitor current utilizing
a current transducer and then the PS current signal.

In addition to the new top-off mode interlocks outlined above, it will
be necessary to design a new interlock system for the booster tunnel.
Tunnel access will be prohibited with the booster RF on. Currently the
booster RF power is low enough to allow access with the system on. The
interlock scheme will resemble the storage ring, with a prohibited
access high power mode and a limited access low power mode.

All personnel protection interlock systems mentioned in this subsystem
will be implemented in a fully redundant way.

##  {#section .unnumbered}

## Accelerator Physics Studies

### Vertical emittance reduction in the Storage ring

The main possibilities to increase the brightness of the ALS are
increasing the time-averaged current, reducing the beam size, and
reducing the insertion device gaps. Currently those changes would result
in (unacceptably) short lifetime. With continuous injection (top-off),
the importance of this lifetime impediment will become significantly
reduced in the future. Figure 1.2-2 shows a comparison of the brightness
of planned, new ALS insertion devices with the upgraded beam parameters
to the typical brightness of a current ALS undulator. One of the main
improvements comes from a smaller vertical emittance and the smaller
physical gaps of the undulators.

#### Simulation of Emittance Correction

A number of simulations were performed to find the smallest number of
individual skew quadrupoles, which still allow an effective emittance
correction, as well as a good distribution of these skew quadrupoles and
finally an optimum correction algorithm. The result was that 12 skew
quadrupoles (one in each sector) were sufficient, six of them located at
high dispersion points and six of them at lower dispersion points with a
larger product of horizontal and vertical beta-functions. In the
simulations many different minimization algorithms were used, but it
turned out, that orbit response matrix analysis (using Matlab LOCO) to
fit an effective skew quadrupole distribution gave results as good as
the best other minimzation algorithm. Since it has the advantage of
requiring very few iterations and automatially providing a measurement
of the local coupling everywhere along the ring it is perfectly suited
to be used with measurement data on the real machine. The simulations
were also used to optimize the parameters of LOCO like the weight factor
of the dispersion function, the outlier rejection tolerance, and the
number of singular values. Figure 3.3-25 shows the results of one of
those simulation runs for 100 random seeds of misaligned machines. In
this particular case it was possible to correct the vertical emittance
below 5 pm using 12 skew quadrupoles for 25% of the error seeds. Some
details of the random error distribution are pessimistic compared to the
errors we find in the real machine. In addition, all seeds that in the
simulations could not be corrected to emittances below 30 pm have one
specific error type, which could if necessary be resolved relatively
easily by realigning a few storage ring magnets.

![](media/image32.png){width="3.640277777777778in"
height="5.114583333333333in"}

[]{#__RefHeading___Toc91568045 .anchor}Figure 3.3‑25: Histograms showing
the results of simulated vertical emittance and dispersion correction
for 100 randomly misaligned error seeds.

The skew quadrupoles at the ALS are integrated in the sextupoles and
used to be connected in 4 chains. Based on the simulations, individual
power supplies were installed two years ago, powering 24 individual skew
quadrupoles - at least one in every sector. Two sectors have four skew
quadrupoles each to generate a closed dispersion bump for the fs-slicing
experiments.

#### Measurements

Because of the resolution limit even of x-ray beamlines it is quite
difficult to measure emittances in the few pm range accurately. The
primary beamline to measure emittances at the ALS uses an imaging optics
with a KB-mirror pair, carbon filters to select the x-ray wavelength
(1.5keV) and to attenuate, a BGO crystal to convert to visible light and
a microscope with CCD. Even though the fundamental resolution limit
would allow a direct measurement of emittances of a few pm, aberrations
of the optics create a larger limit. Therefore we used three somewhat
indirect but independent methods to measure the very small vertical
emittances.

The first method was to determine the resolution of the beamline using
Touschek lifetime measurements for various beamsizes. We then corrected
the beamsize measurements for the beamline resolution to deduce the real
vertical emittance. The second method was based on the analysis of an
orbit response matrix, using a large number of skew gradient error fit
parameters. With the calibrated machine model one can then calculate the
vertical emittance using a lattice code. The final method used a scan of
the RF-acceptance while measuring the Touschek lifetime. For low RF
amplitudes, the Touschek lifetime is strictly proportional to the bunch
volume. Therefore one can deduce a very small emittance from a beamsize
measurement at moderate coupling.

All three methods gave consistent results. In the best case, the
measured vertical emittance as determined by the three methods was 4-7
pm, corresponding to an emittance ratio of less than 0.1% at 1.9 GeV
(natural emittance is 6.75 nm). Figure 3.3-26 shows an example of the
change in beamsize and local tilt angle in one iteration of the
emittance correction. The mean value of the emittance measurements of
about 5 pm was to our knowledge a world record in 2003 for vertical
emittances in electron/positron storage rings and is virtually identical
to the design value for the NLC damping rings. It is interesting to note
that emittances this small are within one order of magnitude of the
theoretical limit due to the finite opening angle of the synchrotron
radiation emission.

![](media/image33.png){width="4.69375in" height="3.68125in"}

[]{#__RefHeading___Toc91568046 .anchor}Figure 3.3‑26:
Horizontal/vertical beamsize and beam tilt as calculated from calibrated
machine model using orbit response matrix analysis. The blue case is
before coupling correction, the green one after one iteration.

#### Emittance Control

Until the full energy injector upgrade at the ALS is finished to allow
top-off injection, it is important to still operate with artificially
increased vertical emittance to achieve reasonable beam lifetimes for
users. Historically at the ALS a controlled excitation of the nearby
linear coupling resonance has been used to increase the vertical
beamsize. After installing the individual skew quadrupoles, we switched
to a different scheme. The emittance and vertical dispersion is
corrected and then 12 skew quadrupoles are used such as to introduce a
global vertical dispersion wave, without introducing coupling. In that
case, the vertical emittance is generated directly via quantum
excitation. The local emittance ratio around the ring can be made fairly
flat and all local

tilt angles are small.

The main advantages of this method are a better beamsize stability
(especially for scanning undulators/wigglers), better dynamic (momentum)
aperture and less sensitivity of the momentum aperture to the vertical
physical aperture. An example of the improvement in longtime beamsize
stability can be seen in Figure 3.3-27.

![](media/image34.png){width="3.2069444444444444in"
height="2.6881944444444446in"}
![](media/image35.png){width="3.1993055555555556in" height="2.68125in"}

[]{#__RefHeading___Toc91568047 .anchor}Figure 3.3‑27: Vertical beamsize
for two four day periods. Using a global vertical dispersion wave to
increase the vertical emittance (right) leads to a much better beamsize
stability than excitation of the coupling resonance (left).

#### Beam Dynamics at low Emittance

Since the lifetime at all (low energy) third generation light sources is
(strongly) Touschek limited, the momentum aperture of the ring is very
important. For top-off operation, injection efficiency becomes very
important as well (i.e. on-energy dynamic aperture). For most light
sources the dominant factor for the momentum aperture is the transverse
single particle dynamics and in most cases the particles are lost on the
narrowest vertical apertures. Therefore it is important to understand
and optimize the dependence of the momentum aperture on the vertical
physical aperture.

We found that for the current ALS lattice the dependence of the momentum
aperture (lifetime) on the vertical physical aperture became much weaker
both for the case with corrected vertical emittance and the case with
vertical dispersion wave, compared to the case with artificially excited
coupling resonance (compare Figure 3.3-28). Combined with the
improvements in the lattice implemented two years ago and better
correction of lattice symmetry errors this will enable the ALS to reduce
the physical gap of insertion devices from the current 8-9 mm down to
about 5 mm.

![](media/image36.png){width="4.638888888888889in" height="3.76875in"}

[]{#__RefHeading___Toc91568048 .anchor}Figure 3.3‑28: Measured lifetime
of the ALS versus half aperture in one straight for three different
cases: excited coupling resonance (red), corrected coupling and vertical
dispersion (green), vertical dispersion wave (blue). The two cases with
excited coupling resonance and dispersion wave were measured for
identical vertical emittance.

Simulating the effects in tracking, we found good agreement between
measurements and simulations. The simulations showed that a correction
of the coupling reduces the sensistivity of the dynamic momentum
aperture to the vertical physical aperture. The injection efficiency for
smaller vertical gaps was studied as well and no show stoppers were
found so far. It is planned to install a collimator system to protect
all insertion devices in the ALS from injection losses during top-off
operation.

### Operation with smaller vertical gaps in the storage ring

For permanent magnet as well as for superconducting insertion devices
the possible performance depends strongly on the possible minimum gap of
the magnetic structure. Therefore it is important to determine the
minimum physical vertical aperture which can be tolerated with respect
to beam lifetime and injection efficiency. At the ALS the limit used to
be a full vertical aperture of about 8 mm. With an improved lattice,
better correction of the lattice symmetry and especially better control
of coupling it was possible to reduce this limit to a full aperture of
about 5 mm. This was verified by measurements using a scraper at the
ALS. Figure 3.3-29 shows a scraper measurement in the ALS with corrected
coupling and the vertical emittance increased to its current nominal
value of 150 pm by using a vertical dispersion wave. The lifetime
reduction in those conditions is fairly small down to a full vertical
aperture of about 5 mm.

![](media/image37.png){width="4.54375in" height="3.68125in"}

[]{#__RefHeading___Toc91568049 .anchor}Figure 3.3‑29: Lifetime of the
ALS versus half aperture in one straight, measured using a scraper: The
lifetime reduction for a lattice with corrected coupling and vertical
dispersion wave to increase the vertical emittance is small down to a
full vertical aperture of about 5 mm.

### Linac to booster transfer efficiency

The injection efficiency into the booster is currently only about 25%.
Because of this, the Linac is running with much larger per bunch charge
than necessary, increasing its beam loading and therefore the output
energy spread. This is an area where significant improvements seem
possible. Therefore detailed studies have been started, investigating
whether different RF settings (cavity coupling, synchrotron tune),
different lattice settings (tune), better orbit correction or the use of
the existing sextupoles to correct the chromaticity can improve the
situation.

### Booster to Storage ring transfer efficiency

During top-off we assume that we can inject 1.5 mA per pulse. Presently
it is possible to achieve 1.5 mA per pulse in 4 bunches with nearly 100%
injection efficiency into the storage ring. This is done with insertion
device gaps opened and with a minimum vacuum chamber aperture of 8.9 mm
full gap. With top-off we need to inject with insertion devices closed.
Also the minimum vacuum chamber aperture will be as small as 5 mm. Our
preliminary machine studies have shown a 40% reduction in injection
efficiency with IDs closed and a vertical scraper with a 5 mm aperture.
The plan for Top-off is to inject with a longer train, up to 10 bunches,
and to improve the injection efficiency.

![](media/image38.png){width="5.833333333333333in" height="4.375in"}

[]{#__RefHeading___Toc91568050 .anchor}Figure 3.3‑30: Dependence of ALS
injection efficiency (without re-optimization) on insertion device
settings. Only the W11 wiggler reduces the injection efficiency
significantly. Because the integration time of the storage ring current
monitor is not exactly matched to the injector period, the measurements
have some jitter around the correct values. This also explains why some
of the measurements indicate injection efficiencies above 100%.

![](media/image39.png){width="5.833333333333333in" height="4.375in"}

[]{#__RefHeading___Toc91568051 .anchor}Figure 3.3‑31: Dependence of ALS
injection efficiency on the vertical physical aperture in the storage
ring without any re-optimization. The aperture was changed by opening
and closing two vertical scrapers in straight 3 at a beta function of
about 6 m.

### Minimizing radiation levels

Since the steady state radiation levels on the accelerator floor and the
potential radiation damage to permanent magnet insertion devices are
extremely important issues with top-off, accelerator physics studies of
those issues were started early in the project and will continue
further, eventually leading to a full radiation safety review.

At the ALS, most particle losses occur in the vertical plane, for all
three main modes of particle loss, namely injection, lifetime losses,
and (RF abort) beam dumps due to equipment failures. The mechanisms in
all cases are somewhat different, but vertical scrapers can be used to
localize losses for all three cases, thereby reducing the steady state
radiation levels on the floor and protecting permanent magnet insertion
devices.

The first mechanism studied in detail was RF beam aborts, which happen
whenever there is any kind of equipment failure at the ALS, since the
interlock systems simply switch off the RF power. We found both in
simulations and using turn-by-turn beam position monitors, that after
the particles start to lose energy (with the RF off), the beam loss
happens around 200-250 turns and is not caused by position shift due to
dispersion, or resonant single particle losses due to resonances, but
rather due to the vertical tune getting close to the integer resonance
and therefore the closed orbit exploding.

After understanding the loss mechanism due to RF aborts, we used the
existing pair of vertical scrapers to attempt to minimize the radiation
levels at the first beam line optics. The current scrapers are installed
at the end of straight 3, not too far upstream from one of the JH
locations (3-1) found in the simulations in Section 3.2.3.5 to be
effective, however at a lower vertical beta function (about 6 m versus
24 m). Using this one scraper and closing it slightly more than the
narrowest existing aperture in the ring, it was possible to reduce the
radiation levels at the beamline 4 first optics by about a factor of 4
(Figure 3.3-32). Even with just one scraper, this would more than
compensate for the about 2 times higher dose rates due to the higher
average currents at which beam dumps will occur in the future. Using
larger numbers of scrapers will further improve the situation.

![](media/image40.png){width="4.881944444444445in" height="5.21875in"}

[]{#__RefHeading___Toc91568052 .anchor}Figure 3.3‑32: Reduction in
radiation dose at first optics in beamline 4.0 due to ALS beam dump
using a vertical collimator at the end of straight 3. The vertical axis
shows average count rates of radiation monitors and the horizontal axis
is time in minutes. Shown are 3 (intentional) beam dumps with equal
stored beam current. After the first dump with scraper open, the scraper
(at a vertical beta function of about 6 m) was set to a full aperture of
8 mm for the second, and 5 mm for the third beam dump.

Future studies will focus on the effectiveness of scrapers (both the
existing ones and the ones to be installed next year) to localize
injection and stored beam (lifetime) losses.

## Injector Reliability

###  Scope

This section reviews the reliability of injection system components.

An overview of injection system components is presented in section
3.4.2. Section 3.4.3 describes the present mode of injection system
operation and compares it to the mode proposed for top-off operation.
Section 3.4.4 lists the component failures that occurred over a recent
twelve-month period and discusses the typical times required to repair
components.

###  Injection System Components

The injection system consists of six subsections: Electron Gun (**EG**),
Linac (**LN**), and Booster Synchrotron (**BR**), and the three beam
transport sections, Gun-to-Linac (**GTL**), Linac-to-Booster (**LTB**)
and Booster-to-Storage Ring (**BTS**).

The electron gun operates at 120 kV and uses a dispenser type thermionic
cathode that is positively biased with respect to the control grid.
Electron bunches are generated with an 8 ns time structure by a 125MHz
grid-to-cathode modulating voltage. The number of gun bunches per macro
pulse is controlled by the length of time the 125 MHz voltage is gated
on.

The linac is a 3 GHz traveling wave structure that accelerates the
electron bunches to 50 MeV. It consists of two accelerating sections
(**AS1** and **AS2**), each 2 m in length. The accelerating sections are
powered by separate 30 MW klystrons (**KLY1** and **KLY2**), which are
driven by pulsed power modulators (**MOD1** and **MOD2**). Attached to
the front end of AS1 is an S-band buncher that is also powered by KLY1.
Additionally, there are two subharmonic bunchers in the GTL section. One
operates at 125 MHz (**SHB1**) and the other at 500 MHz (**SHB2**). A
separate amplifier system drives each buncher.

The booster synchrotron has a FODO lattice structure with four-fold
symmetry. It uses two families of quadrupole magnets (**QF** and **QD**)
which are powered in series, with a separate power supply for each
family. Likewise, a single power supply powers the bend magnets. The two
families of sextupole magnets (**SF** and **SD**) have not been
commissioned. The four horizontal (**HCM**) and four vertical (**VCM**)
corrector magnets in each sector are powered by individual power
supplies. A fast kicker magnet (**BR1 KI**) steers the beam on orbit at
injection; three bump magnets, a fast kicker (**BR2 KE**), and thin and
thick septum magnets (**BR2 SEN** and **SEK**) extract the beam. The RF
accelerating cavity is powered by a 15 kW klystron.

The EG, GTL, LN, LTB and BTS sections have a total of 5 solenoid, 22
quadrupole, 8 bend and 32 corrector magnets. Each of these magnets is
controlled with a separate power supply.

### Injector Operating Mode

The injection system operates at 1 Hz rep rate. The storage ring is
filled three times a day, at 8 hr intervals, and at other times if
faults occur.

Normal user operations consist of 5-6 day periods of continuous, 24
hr/day operation. A one or two-day maintenance shutdown and/or one day
of machine studies conducted by the Accelerator Physics group follows
each user period. An experimental facility in the BTS area, designed to
use booster beam when the booster is not needed for storage ring
injection, runs periodically. When the BTS experiment is taking beam,
the booster is pulsed 8 hr/day, 5 days/wk for one to two week intervals.

The egun cathode is kept at the nominal operating temperature at all
times. The gun high voltage is turned off when beam is not needed for
tuning or injection into the storage ring.

The bunchers, linac and booster RF systems are pulsed continuously at 1
Hz. The GTL, LN, and LTB magnets are at nominal operating currents at
all times. The BR bend, quadrupole and corrector magnets are always on;
booster pulsing is stopped when the system is not in use. The booster
injection and extraction, and storage ring injection pulsed magnets are
turned off when not needed for tuning or injecting beam into the storage
ring. The BTS bend magnets are turned off when not needed for injection.
All other BTS magnets are kept at their nominal operating currents.

Aside from the upgrade of the injection system to full energy (1.9 GeV),
the operational conditions for top-off operation would not change
significantly from the normal fill mode. The differences would be: (1)
All magnet power supplies stay on continuously. During the periods
between injection cycles, pulsed magnet triggers are disabled. (2) The
gun HV remains on; gun output is blocked by inhibiting the gun gate
trigger. (3) The booster ramp rate is reduced from 1 to 0.5 Hz. Because
of the similarity of the two operational modes, the reliability of most
components is expected to be similar. An exception is the pulsed
magnets; the increased duty cycle of these components may increase the
failure rate.

### Injection System Component Failures

A review of injection system performance over a recent 12-month period
provides an overview of the type of failures that can be expected. The
table below shows the component faults/failures that occurred between 1
Oct 03 and 1 Oct 04. Also shown is the number of occurrences of the
fault and the mean-time-to-repair (MTTR), or recover, from the event.

[]{#__RefHeading___Toc91568097 .anchor}Table 3.4‑7: Injection System
Faults/Failures 1 Oct 03 to 1 Oct 04

+-------------------------------------------------------+------+-------+
|                                                       | No.  | MTTR  |
|                                                       |      |       |
|                                                       | Ev   |       |
|                                                       | ents |       |
+-------------------------------------------------------+------+-------+
| EG                                                    |      |       |
+-------------------------------------------------------+------+-------+
| HV supply -- current clamp at turn on (cleared by     | 3    | 0.25  |
| off/on cycle)                                         |      | min   |
+-------------------------------------------------------+------+-------+
| Heater fault - vacuum interlock chassis intermittent  | 6    | 3 min |
+-------------------------------------------------------+------+-------+
| GTL IP vacuum fault                                   | 1    | 5 min |
+-------------------------------------------------------+------+-------+
|                                                       |      |       |
+-------------------------------------------------------+------+-------+
| MOD 1 and 2                                           |      |       |
+-------------------------------------------------------+------+-------+
| Waveguide and accelerator vacuum                      | 8    | 3 min |
+-------------------------------------------------------+------+-------+
| PFN HV supply -- overvoltage                          | 4    | 5 min |
+-------------------------------------------------------+------+-------+
| PFN HV cable arc (replaced)                           | 1    | 1.6   |
|                                                       |      | hr    |
+-------------------------------------------------------+------+-------+
| Thyratron failure                                     | 1    | 3 hr  |
+-------------------------------------------------------+------+-------+
| Computer controls (ILC)                               | 1    |       |
+-------------------------------------------------------+------+-------+
|                                                       |      |       |
+-------------------------------------------------------+------+-------+
| KLY 1 and 2                                           |      |       |
+-------------------------------------------------------+------+-------+
| 800W RF amplifier failure                             | 1    | 1 hr  |
+-------------------------------------------------------+------+-------+
| RF input -- 500MHz to 3GHz multiplying chassis        | 1    | 2 hr  |
| failure                                               |      |       |
+-------------------------------------------------------+------+-------+
|                                                       |      |       |
+-------------------------------------------------------+------+-------+
| Linac                                                 |      |       |
+-------------------------------------------------------+------+-------+
| Water temperature controller failure                  | 1    | 30    |
|                                                       |      | min   |
+-------------------------------------------------------+------+-------+
| Solenoid power supply failure                         | 1    | 1.2   |
|                                                       |      | hr    |
+-------------------------------------------------------+------+-------+
|                                                       |      |       |
+-------------------------------------------------------+------+-------+
| LTB                                                   |      |       |
+-------------------------------------------------------+------+-------+
| Q4.1 power supply -- AC breaker trip                  | 2    | 5 min |
+-------------------------------------------------------+------+-------+
| Q4.1 power supply -- defective fan, replaced supply   | 1    | 30    |
|                                                       |      | min   |
+-------------------------------------------------------+------+-------+
|                                                       |      |       |
+-------------------------------------------------------+------+-------+
| Booster                                               |      |       |
+-------------------------------------------------------+------+-------+
| Septum box vacuum fault                               | 2    | 1 min |
+-------------------------------------------------------+------+-------+
| RF cavity IP spark down                               | 2    | 2 min |
+-------------------------------------------------------+------+-------+
| Klystron, intermittent overtemperature fault          | 2    | 5 min |
| (defective meter                                      |      |       |
|                                                       |      |       |
| replaced during maintenance)                          |      |       |
+-------------------------------------------------------+------+-------+
| Girder water fault                                    | 1    | 21    |
|                                                       |      | min   |
+-------------------------------------------------------+------+-------+
| SEN and SEK HV power supply failure                   | 2    | 30    |
|                                                       |      | min   |
+-------------------------------------------------------+------+-------+
| KI and KE HV power supply failure                     | 5    | 30    |
|                                                       |      | min   |
+-------------------------------------------------------+------+-------+
| KI arcing in PFN chassis (loose ground wire)          | 1    | 1.9   |
|                                                       |      | hr    |
+-------------------------------------------------------+------+-------+
| QF power supply capacitor bank failure                | 1    | 3.5   |
|                                                       |      | hr    |
+-------------------------------------------------------+------+-------+
| BTS                                                   |      |       |
+-------------------------------------------------------+------+-------+
| Girder water flow meter failure (Keptrol controller   | 1    | 30    |
| replaced)                                             |      | min   |
+-------------------------------------------------------+------+-------+
| Corrector magnet power supply failure                 | 1    | 30    |
|                                                       |      | min   |
+-------------------------------------------------------+------+-------+
| Power supply rack water fault (flow turbine failure)  |      | 51    |
|                                                       |      | min   |
+-------------------------------------------------------+------+-------+
| Bump magnet grounding and trigger chassis - relay     | 1    | 1.9   |
| failure                                               |      | hr    |
+-------------------------------------------------------+------+-------+
| Bump power supply -- sled timing and firing           | 2    | 2.4   |
|                                                       |      | hr    |
+-------------------------------------------------------+------+-------+
| Power supply rack, AC power phase fault (defective    | 1    | 3.5   |
| breaker)                                              |      | hr    |
+-------------------------------------------------------+------+-------+
| B1 bend magnet power supply overcurrent -- firing     | 1    | 3.5   |
| circuit                                               |      | hr    |
|                                                       |      |       |
| SCR failure                                           |      |       |
+-------------------------------------------------------+------+-------+
| SEK power supply airflow. Interlocked rack fan,       | 1    | 4.5   |
|                                                       |      | hr    |
| not shown on print, off                               |      |       |
+-------------------------------------------------------+------+-------+
| B4 power supply intermittent air flow fault           | 3    |       |
| (defective vane switch)                               |      |       |
+-------------------------------------------------------+------+-------+
| Power supply computer controls (ILC)                  | 4    |       |
+-------------------------------------------------------+------+-------+

The electron gun is relatively trouble free. A cathode typically last
about 5 years. Replacements are scheduled; no cathode has failed
catastrophically. Should the 120 kV high voltage supply fail, it can be
replaced in about 30 min.

Two recent E-gun problems involved cathode heater faults and overcurrent
clamps of the HV power supply. The heater faults were intermittent and
were caused by ripple on a power supply in a vacuum interlock chassis.
Recovery time was minimal with the cathode returning to operating
temperature within 2-3 minutes. The HV power supply overcurrent clamps
occurred when the power supply was turned on. A simple off/on cycle of
the supply cleared the clamp within seconds.

The subharmonic bunchers have rarely presented a problem; only SHB2 has
had a significant failure. In Sept 97, the 100 W pulsed driver and a
tube and resistor string in the power amplifier failed. The driver was
replaced with a spare. The amplifier failures only caused the buncher
gradient to sag over the 20 microsecond flattop of the pulse and could
wait for a maintenance day to repair.

The most common linac modulator problems are arcing at connections in
the pulse forming network or failure of the high voltage PFN charging
supply. Arcing problems are usually resolved in 1-2 hr and involve
cleaning and retightening the connection and occasionally replacing a
damaged cable. If an HV charging supply fails, it can be replaced in
about 30min. The thyratron that fires the PFN usually is good for about
2 yr. The tubes show signs of aging (time jitter or occasional break
down) before failing and are usually replaced on a scheduled basis;
replacement takes about 3 hr. PFN capacitor failures have not
interrupted operation. Capacitors are periodically inspected during
maintenance periods and those showing signs of leakage are replaced.

One of the klystrons (KLY1) is original to the facility and has logged
approximately 77,000 hr of operation. The other, KLY2, was installed in
Mar 98 and has logged approximately 47,000 hr of operation. The original
klystron powering AS2 failed at approximately 30,000 hr. When
replacement is required, a spare klystron can be installed in about two
shifts. The most likely klystron component to fail is the buncher
cavity, 800W RF amplifier. Replacing this amplifier takes about 1 hr.

The most common booster component failures are the kicker magnet HV
charging supplies and thyratrons and the septum magnet HV supplies.
Thyratrons take about 3 hr to replace and can usually be deferred for
replacement until a maintenance day. Kicker and septum magnet HV
supplies can be replaced in about 30 min. The booster quadrupole and
bend magnet power supplies occasionally fail and can take hours to
repair. Failed capacitors or SCRs can usually be identified and replaced
in 3-4 hr. Other problems, such as those involving logic circuitry, can
take 8 hr or more to resolve. The booster RF system has been relatively
trouble free. The only exceptions are two problems that occurred with
the klystron HV supply that took 3-4 hr to resolve. One was arcing
inside the supply at one of the connections. The other was failure of
the vacuum contactor that connects the HV supply to the klystron.

The BTS elements requiring the longest time to repair are the high power
supplies that power the bend magnets. The components most likely to fail
in these supplies are the SCRs. Identification and replacement of failed
SCRs can take 3-4 hr.

At the downstream end of the BTS line, in the storage ring injection
straight, are the pulsed septum and bump injection magnets. The most
common problem with the septum magnets is failure of an HV supply.
Typically, an HV supply can be replaced in about 30 min. Bump magnet
failures take more time to resolve and usually involve the sleds. Sled
failures usually take 2-3 hr to resolve.

The power supplies powering individual injection system DC magnets
rarely present a problem and are easily replaced. Most supplies can be
replaced in about 30 min.

Other common faults are accelerator vacuum faults and magnet and power
supply water faults. Vacuum faults typically result from an ion pump
sparking down or drawing excessive current because of aging. Problems
with high current draw are normally cleared in a few minutes by cycling
the IP power. Water flow faults are often not the result of real flow
problems but rather a problem with either the flow turbine or associated
electronics. The turbine or controller can be replaced in about 30 min.

Most injection system failures can be resolved in less than an hour.
Some components responsible for longer duration failures will be
upgraded to accommodate the increased beam energy in top-off mode. These
include the fast pulsed magnet power supplies (BR2 KE, BR and SR septa,
SR bump), and the booster series magnet and BTS bend magnet power
supplies. While the reliability of the upgraded systems will not be
known initially, it is likely, due to the nature and complexity of the
systems, that they will continue to be a source of injection system
failures.

## Pulsed Magnets

### Introduction

ALS top-off mode of operation will require injection of the electron
beam from the Booster ring (BR) into the Storage Ring (SR) at the full
ALS energy level (1.9GeV). Currently Booster delivers 1.5GeV[^1] beam to
the Storage Ring where it is ramped to the full energy and then stored
for the user operation. Higher Booster beam energy will require the
Booster and Storage Ring pulse magnets to operate at proportionally
higher magnetic gap fields. To better understand the breadth and scope
of the pulse magnet capabilities and future requirements for 'topoff'
our group posed the following basic questions:

1)  What are the engineering design and installation (EDI) modifications
    necessary to operate at 1.9 GeV[^2] 'topoff' mode? To have
    sufficient design margin

    a.  Can we use existing pulse magnets?

    b.  What's required to drive the existing pulse magnets?

2)  What are the EDI modification necessary to minimize storage beam
    instability during 'topoff' operations?

    a.  For the storage ring Septa:

        i.  Do we need to improve eddy current shielding of thick septum
            magnet?

    b.  For the storage ring Bumps:

        i.  Can we understand and minimize the vertical kick of the
            stored beam by the bump magnet operations?

3)  What are magnitudes of the increased stresses and the estimates for
    life expectancy for the various pulse magnet systems?

Our work over the past seven months is reflected in the report that
follows.

### Pulsed magnet operation

Extraction from the booster ring into the transfer line and injection
from the transfer line into the storage ring is achieved by activating a
combination of slow bumps, kickers, septa magnets in the booster ring
(BR) and set of fast bumps and septa magnets in the storage ring (SR).
The configuration of these pulse magnets is shown in Figure 3.5-33
(booster extraction) and Figure 3.5-34 (storage ring injection).

The extraction/injection magnets are nominally used to fill the storage
ring at a 1 Hz rate with three bunches spaced 8 ns apart during each
booster ramping cycle. The nominal injection energy is 1.525 Gev. During
the normal injection process the magnets are operated continuously at a
1 Hz pulse rate until the storage ring has been refilled from a nominal
base level (200 ma) to a peak current of 400 ma. Depending on the
injection rate (0.7 to 0.8 ma/shot) the process takes about six minutes
or 360 shots to refill the storage ring. In the 'topoff' mode magnets
will be driven at 28% higher fields to accommodate the full injection
energy of 2.0 Gev and will pulsed once every 20 sec, continuously.

![](media/image41.png){width="5.804861111111111in" height="4.65625in"}

[]{#__RefHeading___Toc91568053 .anchor}Figure 3.5‑33: Booster extraction
magnets.

Key:

BR2_BMP1-3 are the 3 booster bump magnets

BR2_KE1 - KE4 are booster kickers

BR2_SEN is thin septum

BR2_SEK is thick septum

![](media/image42.png){width="5.995833333333334in"
height="4.677777777777778in"}

[]{#__RefHeading___Toc91568054 .anchor}Figure 3.5‑34: Storage Ring
injection area.

Key:

SR01S_BUMP1 to BUMP4 are Bump magnets

SR01S_SIK is Thin Septum

SR01S_SIN is Thick Septum

A brief outline of the extraction/injection process follows and is shown
in Figure 3.5-35:

1)  5 ms before beam extraction from the BR three 'slow' bump magnets
    are energized

2)  50 us before beam extraction two 'thin' septa magnets are energized

    a.  One in the extraction and one in the injection sections

3)  10 us before beam extraction the two 'thick' septa magnets are
    energized

    a.  One in the extraction and one in the injection sections

4)  2 us before beam extraction the four SR 'fast' bumps are energized

5)  75 ns before beam extraction the four BR 'fast' extraction kickers
    are energized

![](media/image43.wmf)

[]{#__RefHeading___Toc91568055 .anchor}Figure 3.5‑35: Timing diagram for
booster/storage extraction/injection magnets. Time periods not to scale

Details of the magnet structures, our investigations and conclusions for
each magnet will be discussed under their specific headings

### Booster bumps analysis:

The extraction of the booster beam is initiated by a full-sinusoidal
excitation (T~full~ = 20ms) of three corrector bump magnets in the
booster. The magnets when excited produce a local closed orbit
distortion in the extraction area of the Booster Ring where the fast
kicker magnets can be energized to direct the beam into the extraction
septa magnet channel. The location of the Bump Magnets in the Booster
extraction line is shown in Figure 3.5-36.

![](media/image44.png){width="5.083333333333333in"
height="3.4270833333333335in"}

[]{#__RefHeading___Toc91568056 .anchor}Figure 3.5‑36: Location of
booster extraction magnets.

Each of the three Bump Magnets has the same core and coil geometry[^3].
See Figure 3.5-37. The magnets have laminated steel cores with a window
frame design to minimize magnetic stores energy and pulse power
requirements. The cores are split on the horizontal mid-plane to permit
assembly of the coils and to allow installation of the magnets around
the stainless steel vacuum chamber. The coils are made of square hollow
copper conductor with saddle shaped ends and will operate satisfactorily
at 1 Hz pulse rate with only natural convection cooling.

The one of three identical capacitor discharge circuits is shown in
Figure 3.5-38.

![](media/image45.png){width="5.833333333333333in"
height="5.333333333333333in"}

[]{#__RefHeading___Toc91568057 .anchor}Figure 3.5‑37: Bump Magnets core
and coil geometry

![](media/image46.png){width="5.996527777777778in"
height="1.336111111111111in"}

[]{#__RefHeading___Toc91568058 .anchor}Figure 3.5‑38: Basic discharge
circuit

This set of magnets and drivers has been intentionally over-designed to
accommodate the original 10 Hz operation and a special high energy
injection scan mode. As a result we simply needed to calculate nominal
source currents and B fields at 2.0 Gev (1.9 Gev + 5% overage)[^4] and
confirm that the driver and magnets could reach these values. The
current nominal injection energy is 1.522 Gev and is listed as 1.5 in
the subscript.

  ---------- ---------- ---------- ---------- ---------- ---------- ----------
  Magnet \#  B~1.5~     B~1.9~     I~1.5~     I~1.9~     ∠~1.5~     ∠~1.9~

             (Kgauss)   (Kgauss)   (Amps)     (Amps)     (mrad)     (mrad)

                                                                    

  B1         2.13       2.74       138        178        5.311      5.311

  B2         -3.67      -4.72      -238       -306       -9.16      -9.16

  B3         1.44       1.85       93         120        3.579      3.579
  ---------- ---------- ---------- ---------- ---------- ---------- ----------

[]{#__RefHeading___Toc91568098 .anchor}Table 3.5‑8: Current and future
operation parameters for booster extraction bump magnets.

**Equipment used for evaluation of magnets at 2.0 GeV:**

a)  **Gauss meter and sensor:** The model YR100-3-2 is a self contained,
    high linearity, high stability magnetic field to analog voltage
    transducer for one component of a magnetic field. It is particulary
    appropriate for magnetic fields up to 2T with better than 0.1%
    absolute accuracy at 1T and with a frequency response from dc to 10
    kHz. Probe is guaranteed flat to 1.0 kHz

b)  **Magnet current sensor:** Pearson 101 current probe

c)  **Monitor scope:** TDS5000 digital oscilloscope

**Results of magnetic field measurements:**

The waveform for BR-2 the magnet with the highest required drive is
shown in Figure 3.5-39. The transfer function of peak current vs. peak
field is shown in Figure 3.5-40.

![](media/image47.wmf){width="5.998611111111111in"
height="4.503472222222222in"}

[]{#__RefHeading___Toc91568059 .anchor}Figure 3.5‑39: Waveform pictures
taken at peak drive current of 312 amps

For magnet Bump #2.

Color code:

Yellow is magnet current @ 100 amp/volt

Turquoise is applicd voltage @ 100 volts/volt

Purple is B field measured with Hall elemet @ 4000 gauss/volt

![](media/image48.wmf)

[]{#__RefHeading___Toc91568060 .anchor}Figure 3.5‑40: Field versus
current transfer function for the second booster extraction bump magnet.

**Key notes for graph #1:**

1)  The thin (\~3mm) Hall probe was placed directly on top of the beam
    pipe on axis with the beam center line.

2)  Only central bump magnet (B2) was measured for following reasons:

    a.  Only magnet where center axis of magnet above the beam tube
        could be accessed by Hall probe.

    b.  From calculationsError: Reference source not found B2 has the
        highest current requirements.

3)  Calculated data points for 1.522 and 2.0 are colored square and
    triangle

    a.  Both points are \~10% below the measured values. This
        discrepancy may be due to short length of the magnet and the
        difficulty in determining the true magnetic length of the magnet

4)  Measurement anomaly: Off axis (from beam center line) B field
    measurements increased linearly up to approximately 1.5 x 5280 =
    7920 gauss. This effect was not investigated but may be due E field
    coupling from the adjacent magnet conductors and Hall probe
    electronics during the pulse.

#### 

Summary:

1)  From graph #1 above the nominal B fields for 2.0 Gev operation were
    reached with sufficient headroom.

2)  Higher field measurements indicate some nonlinear effects in the
    measurement but this is well above the nominal operating point.

3)  Conversion to water cooling at 2.0 Gev operation is not necessary

    a.  A 29% increase in current or 65% increase in power multiplied by
        1/2 Hz cycle rate results in a --17.3% decrease in magnet power
        dissipation.[^5]

### Booster Fast extraction Kicker:

At approximated 145 ns before beam is extracted from the booster four
Thyratron triggered, charge line type, kicker power supplies discharge a
square pulse of current into four 'very fast' single turn window frame
magnets in the booster ring to create the final link of the magnetic
channel to the storage ring. During the initial ALS Top-Off design
process a key question to answer was: "Do we need to modify the Booster
fast extraction kickers for Top-Off operation?".

Extraction Energy: E 1.95\[GeV\]

Beam stiffness at 1.95GeV B~s~ 6.5 \[Tm\]

Required deflection angle- θ 4 \[mRad\]

Effective length of the kicker (4 units) l~eff~ 1.07\[m\]

Required Induction in the kicker air gap:

$B_{\text{Air}} = \frac{B_{s} \cdot \theta}{l_{\text{eff}}} = 0\text{.}\text{024}\text{ T} = \text{240}\text{ G}$
(3.5‑1)

The cross-section of the ALS kicker is shown in Figure 3.5-41.

Since the magnetic flux is the same in the air gap and the ferrite core
the average magnetic induction in the ferrite core equals:

$B_{\text{Ferr}} = B_{\text{Air}} \cdot \frac{S_{\text{Air}}}{S_{\text{Ferr}}} = \text{1603}\text{ G}$
(3.5‑2)

The maximum value of the magnetic induction in the ferrite core was
calculated using INSOFT software and the results are given in Figure
3.5-41.

![](media/image49.png){width="5.997916666666667in"
height="4.395138888888889in"}

[]{#__RefHeading___Toc91568061 .anchor}Figure 3.5‑41: INSOFT Half magnet
simulation of B field @ 2.0 Gev

The maximum B-field in the corners of the ferrite core reaches the value
of 2400 G.

What is still well below the saturation value for CMD 5005 ferrite (3200
G). Calculations also indicated that the nominal DC operating voltage
for the Charge line and Thyratron would rise 30% from 12.5 KV to
approximately 17.0 KV.

Several questions that had to be answered:

1)  Could the existing Balan coupling transformer handle 17kV pulses?

    a.  According to ALS record several transformers failed during 13kV
        dc high-potting tests).

    b.  Construction of transformers is very involved and difficult.

2)  Could the existing CX1157 thyratron operate at 17kVDC?

    a.  Operational experience has shown that the CX1157 in it's
        existing configuration was unable to operate above 16kVDC due
        internal sparking problems.

3)  Could the various subsystem components (charge line cables, etc.)
    stand the higher DC operating voltage?

To answer these questions a kicker test stand shown in Figure 3.5-42 was
constructed.

![](media/image50.jpeg){width="6.754861111111111in"
height="5.563194444444444in"}

[]{#__RefHeading___Toc91568062 .anchor}Figure 3.5‑42: Drawing of kicker
test stand arrangement.

High Voltage Tests results:

1)  The power supply dc voltage was increased slowly from 0 to 20kVdc.At
    16.5kVdc pulse front end forming capacitor (Cf in Fig1) failed. It
    has been replaced with two 1800pF ceramic capacitors each rated for
    40kVdc connected in series.

2)  For voltages around 17-17.5kV occasional discharge inside the brass
    cylinder containing CX1157 thyratron occurred. It has been noticed
    that the clearance between the thyratron body and the thyratron
    brass container tube was very small (less than 13mm). We insulated
    the brass containing tube with two layers of 0.03" thick Teflon
    sheets. Then we were able to increase the dc voltage to 20kVdc
    without any further incidents.

Life test results:

1)  The kicker pulse amplitude was increased slowly from 5 to 17kV (5%
    above

2)  the value required for Top-Off operation mode). We noticed linear
    dependence between the dc power supply voltage and the pulse B-field
    amplitude value over the whole 5 to 17kV range (no sign of
    saturation noticed). The test stand was operated at 17kV level
    with1Hz repetition rate for 3 days.

3)  On day four we increased the repetition frequency to 10Hz and it was
    run in these conditions for the next three weeks until:

    a.  **the reversing diode stuck failed** (D1 in Fig.1). This device
        was designed for current mode of operation and was rated for
        only 16kV (16 1kV diodes in series without reverse voltage
        balancing resistors).

    b.  D1 was replaced with 20kV rated device and the test continued up
        to the full 30days period (24 hours/day) without any further
        incidents.

4)  Upgrading the existing Kaiser Systems Inc (KSI) charging power
    supply to a newer design is currently being investigated.

    a.  The design of a hardware interface is required.

    b.  Several spares with interfaces should be produced.

Summary:

The ALS extraction kicker successfully passed a 30 days endurance test
at the B-field level corresponding to 2GeV ALS beam energy level. In
order to use existing kicker magnets for Top-Off operation we suggest
following modifications:

1.  Change existing pulse front forming capacitors to higher voltage
    handling devices.

2.  Insulate the thyratron containing tube against the possible high
    voltage discharges from thyratron tube.

3.  Replace the existing reversing diode stacks with higher voltage
    handling devices.

4.  The charge-line cables should be replaced

### Booster and Storage ring Thick and Thin septum magnets

Fifty microseconds before the peak of the storage ring orbit bump, the
two identical 'thick' septa magnets, one in the BR extraction straight
and a mirror device in the SR straight, are energized. Thirty
microseconds later the two identical 'thin' septa magnets one in the BR
extraction straight and a mirror device in the SR straight are
activated. See Figure 3.5-33 and Figure 3.5-34 above. The basic
questions that we attempt to answer in this section are: What
modifications to the septa magnets and drivers are required to operate
at 2.0 Gev 'topoff' mode? Are there any changes to the system topology
that can minimize storage beam instability during 'topoff' operations?
And finally what are magnitudes of the increased stresses and the
estimates for life expectancy for the septa magnet systems?

#### Electronic drive requirements for topoff: 

Existing septa drives

The driving circuit for the thick septa is shown in Figure 3.5-43. A low
inductance capacitor is resonantly discharged through a stacked array of
six high voltage, high di/dt SCR's and a series blocking diode. The
resultant current and voltage waveforms are shown in Figure 3.5-44. The
half sine period for the thick septum is \~100us and \~20us for the thin
septum magnet. The thick septum uses an energy recovery inductor to
minimize the charging power supply size and cost. The thin septum has no
energy recovery and requires only two SCR's in series. Both systems
operate at one Hertz.

![](media/image51.wmf)

[]{#__RefHeading___Toc91568063 .anchor}Figure 3.5‑43: Basic discharge
circuit for the thin and thick septum magnet

![](media/image52.png){width="6.0in" height="4.5in"}

[]{#__RefHeading___Toc91568064 .anchor}Figure 3.5‑44: Basic discharge
circuit waveforms for the thick septum magnet

Drive requirements for Topoff:

[]{#__RefHeading___Toc91568099 .anchor}Table 3.5‑9: Thick septum
operational parameters for higher fields:

[]{#__RefHeading___Toc91568100 .anchor}Table 3.5‑10: Thin septum
operational parameters for higher fields (SR thin septum\*):

The increase in the drive requirements for both magnets is 30%. This
presents no real challenge for an upgrade to the drivers. The thick
septa will require a new higher voltage charging supply, capacitors, and
replacement of several lower voltage sub-components. The thin septum
power supply will require a new higher di/dt SCR that is currently being
specified and new charging capacitors. In addition the charging power
supply for the SR thin septum needs to be upgraded. **(\*)**This is due
to an existing +20% over drive condition required for the SR thin septum
magnet. The reason for the overdrive condition is not understood at this
time. A discussion of possible reasons and future investigations is
listed under the topic "Further studies to do". A new higher voltage
spare driver has already been constructed for driving the spare pulse
magnets. This unit is a swappable replacement for both the existing and
future thin and thick septum drivers.

#### Septum magnets:

Mechanical description:

Each thin and thick septum magnet comprise a pulsed bending magnet
system; one system is for extracting the beam from the booster and the
other system, essentially identical, is for injecting the extracted beam
into the storage ring. Figure 3.5-45 shows the injection top view
layout, with each magnet sectioned through the horizontal mid-plane. The
thick septum, named for its thicker septum plate, gives a 10.0 deg bend,
and the thin septum gives a 2.0-degree bend. Both magnets are iron
dominated, with C-shaped cores forming the main magnetic gap, as shown
in Figure 3.5-46 the drive coil is wound around the back leg of the
core. The thick septum has a laminated steel core which can pass a
higher peak B field but requires a longer period (\~100 us) discharge
pulse, and the thin septum has a ferrite core which can pass a lower
peak field, but employs a shorter (\~20) pulse. Both magnets employ an
eddy current septum design that consists of a thin copper sheet placed
against the open end of the C-shaped magnet gap. The fast rise and fall
of the main gap field generates sufficiently high eddy currents in the
longitudinal direction in the copper septum plate to prevent the fringe
field at the end of the gap from penetrating through the septum, thus
allowing a circulating beam to be positioned close to the opposite side
of the septum plate. The return leg eddy current travels through a
similar copper plate on the opposing side of the magnet; these plates
being electrically connected at each end and across the top and bottom
with copper plates and form a "shield box" around the magnet. For
sufficient thickness of the septum (t\>3 skin depths), the total current
in the septum plate closely matches the drive current, which is the case
for both magnets.

![](media/image53.png){width="5.230555555555555in"
height="3.051388888888889in"}

[]{#__RefHeading___Toc91568065 .anchor}Figure 3.5‑45: Top view of Septa
magnet layout -- SR straight. Each magnet sectioned through the
horizontal midplane.

![](media/image54.png){width="3.2708333333333335in"
height="4.239583333333333in"}

[]{#__RefHeading___Toc91568066 .anchor}Figure 3.5‑46: Thick (left) and
thin (right) Septa cross sections -- (needs to be resized)

[]{#__RefHeading___Toc91568101 .anchor}Table 3.5‑11: Thin and Thick
septum fixed parameters

[]{#__RefHeading___Toc91568102 .anchor}Table 3.5‑12: Thick septum
operating parameters

[]{#__RefHeading___Toc91568103 .anchor}Table 3.5‑13: Thin septum
operating parameters (SR thin septum)

#### Theoretical investigations:

Field quality & current distribution in thick septum at 2.0 Gev

Thick Septum:

The thick septum core is made from M-19 electrical steel laminations
each 0.35mm thick. This material retains high permeability even at 1.6
T. The pole-tip fields do not exceed the nominal gap field of 1.33T,
except at a very small corner section where the septum plate meets the
core. Sufficient thickness throughout the core back leg exists to keep
average B in this section below 1.3T. The presence of eddy currents in
the iron laminations during the pulse concentrates the field towards the
outer surfaces of the laminations, thus requiring more MMF in the core
section of the magnetic circuit. To account for this, an eddy current
modified B-H curve was generated for M-19 steel specific to this
lamination thickness and transient time pulse. Using the eddy current
modified B-H curve in a transient finite element model of the magnet
cross section (OPERA-2D), it was verified that only slight local
saturation at the inside corners of the core back leg occur, behind the
conductors. This causes a negligible rise in core MMF and also helps to
maintain field uniformity across the gap (by equalizing the core MMF
along different flux paths).

Figure 3.5-47 shows a plot of the vertical B field component along the
transverse width of the gap at the mid-plane. Three different field
levels are shown, 1.0T (present operation) 1.33T (top off nominal) and
1.5T (13% over top-off nominal); with the two higher field levels
current normalized by the current factor to the nominal current of
present operation for comparison. The magnet efficiency is still quite
good at 1.5T,as the field value in the straight line portion is within
0.2% of the lower value. In all cases, a small amount of highly
localized saturation occurs at the pole tip corner where it meets the
septum, leading to a slight field drop off very close to the septum.
This is due to the field penetration into the septum, as the AC skin
depth is 1.04 mm @ 4 kHz.

![](media/image55.png){width="5.99375in" height="4.235416666666667in"}

[]{#__RefHeading___Toc91568067 .anchor}Figure 3.5‑47: Vertical B field
component along the transverse width of the gap at the mid-plane. For
1.525 Gev, 2.0 Gev, and + 10%

Thin Septum:

Figure 3.5-48 shows similar field plots, with the high current (B=0.40T)
curve normalized to the present nominal current (B=0.30T) across the gap
mid-plane, near the narrow end. One can see that the magnet retains a
high degree of efficiency at the higher field and also maintains a
uniform field closer to the septum. The ferrite used (MN-80) retains
high permeability @ 0.48 T so a 20% safety factor is present. The thin
septum has an AC skin depth of 0.42mm @ 25 kHz leading to less field
falloff close to the septum.

![](media/image56.png){width="5.99375in" height="4.235416666666667in"}

[]{#__RefHeading___Toc91568068 .anchor}Figure 3.5‑48: Thin septum high
current (B=0.40T) curve normalized to the present nominal current
(B=0.30T) across the gap midplane, near the narrow end.

The theoretical results for the thick and thin septum show very
acceptable field quality with good margins at 'topoff' currents levels.
Magnet measurements of the thin and thick septa agree with the model
results and are discussed in the section "Parameter measurements of
septa spares".

#### Improvements in magnet system topology that improve SR beam stability:

Beam position measurements as shown in Figure 3.5-49 show horizontal and
vertical orbit shift in the stored beam during the injection process.
Injection studies show that this effect only occurs when the thick
septum magnet is firing. It had been surmised that a slowly decaying
remnant leakage field penetrates through the eddy current 'thick'
septum. Our theoretical and experimental investigations described below
accurately verify this effect. We also experimentally demonstrate a
modification to the thick septum driver that markedly reduces this
problem.

 

![](media/image57.png){width="5.570833333333334in"
height="3.6444444444444444in"}

[]{#__RefHeading___Toc91568069 .anchor}Figure 3.5‑49: Beam orbit
distortion due to slowly decaying eddy currents in thick septum magnet.

#### Theoretical model eddy current leakages:

The eddy current in the septum plate diffuses into the septum plate over
time and the current profile across the septum has the form of an
exponentially damped traveling cosine wave. Figure 3.5-50 shows both
eddy currents in the thick septum and flux lines in the thick septum at
full field (t=62.5us). At the end of the half sine drive pulse
(t=125us), even though the total current in the septum is zero, this
damped cosine current profile is not zero and forms a very thin vertical
dipole B field in the septum, which can be seen in Figure 3.5-51 as flux
lines entering the core at the corner. A small potion of the total flux
circulates around the left side of the septum (not shown) to produce a
stray field along the circulating beam path. This dipole current has
it's own L/R decay time constant which is relatively long, and, for the
thick septum, the stray field causes a beam orbit distortion shown in
Figure 3.5-49. The thin septum stray field is smaller and is shielded by
thick iron plating inside the beam tube and has little effect on the
beam. Figure 3.5-52 shows the thick septum stray field at its maximum
value, which occurs at 1.0 msec after the start of the half sine current
pulse. The stray field intensity is a function of transverse distance
from the septum, and a field integral of \~500 G-cm maximum integrated
along the beam path is predicted. Figure 17 shows the predicted time
history of this stray field integral. Under top-off mode this persistent
stray field would be present about every 30 sec.

![](media/image58.png){width="5.995833333333334in"
height="4.2340277777777775in"}

[]{#__RefHeading___Toc91568070 .anchor}Figure 3.5‑50: Thick septum at
peak field (1.33 tesla) of half sine pulse

![](media/image59.png){width="5.995833333333334in"
height="4.2340277777777775in"}

[]{#__RefHeading___Toc91568071 .anchor}Figure 3.5‑51: Thick septum at
zero field at end of half sine pulse

![](media/image60.png){width="5.997222222222222in"
height="4.238888888888889in"}

[]{#__RefHeading___Toc91568072 .anchor}Figure 3.5‑52: Thick septum stray
field at its maximum value at 1.0 msec after the start of the 'half
sine' current pulse.

#### Reducing the leakage using a full sine ring:

By using a full sine pulse instead of a half sine pulse, a second
"following" dipole eddy current of opposite polarity is created which
can reduce both the magnitude and the long time duration of the stray
field. Figure 3.5-53 shows the flux lines at the end of a damped full
sine current pulse using a damping factor as measured on the installed
magnets (93.5% voltage reversal) and Figure 3.5-54 shows the time
history of the resulting predicted stray field integral.

#### Experimental results of full ring test:

To test this prediction the present pulse driver was reconfigured to
produce a full sine drive current pulse and the effect on the stored
beam was measured, the beam deflection time-history and FEA calculated
time history of the stray field integral are shown in Figure 3.5-54.
This reduced stray field integral meets the requirements for top off
operation.

![](media/image61.png){width="5.995833333333334in"
height="4.2340277777777775in"}

[]{#__RefHeading___Toc91568073 .anchor}Figure 3.5‑53: Flux lines at the
end of a damped 'full sine' current pulse using a measured damping
factor of (93.5% voltage reversal)

![](media/image62.png){width="4.923611111111111in"
height="3.470138888888889in"}![](media/image63.png){width="3.9993055555555554in"
height="3.0027777777777778in"}

[]{#__RefHeading___Toc91568074 .anchor}Figure 3.5‑54: Predicted time
history of this stray field integral along the beam axis and measured
orbit distortion for half-sine and damped full-sine case.

#### An estimate of the reliability of magnets and expected contingencies:

Lifetime requirements for magnets:

An upper limit of the maximum number of pulses the magnets will endure
in the 'top-off' mode would be: 3 shots/min. \* 60min./hr. \*
6000hr/year \* 10 years = 10.8\*10^6^ pulses. The existing magnets which
have been in operation since 1992 without failure may have very
approximately: 400shots/6hr. \* 6000hr./year \* 12years + 1.2 (special
mode) = 5.7 \* 10^6^ shots. We acknowledge that estimated life left in
the existing magnets is unknown. In the following text we will attempt
to identify any factors that might accelerate the degeneration of the
magnets and will propose a contingency plan in the event of a magnet
failure.

The key factors that could lead to an accelerated failure of the magnets
would be high voltage breakdown at the core to conductor edges,
repetitive magneto-strictive shock, increased heat load of the septum or
the cores and radiation damage to the Epoxy.

Higher voltage breakdown at the core to conductor edges:

The magnet coil is insulated with 2 mm of epoxy/fiberglass insulation.
At each end of the magnets the coil projects past the core edges which
have a sharp corner; they were not radiussed before winding the coil.
The core can be considered to be at ground potential as it makes
intimate contact with the copper shield box along the top , bottom and
back sides of the core (a thin Kapton sheet was inserted between the
septum and the core. A high electrical field gradient occurs at the
start and end of each half sine pulse between the coil and ground. A
possible fix is the addition of a stainless steel "field smoothing
piece". The coil voltage at these locations is close to the full voltage
across the leads. 10.6 million 'full ring' pulses can be very re-scaled
in time to 60 hrs of 50 Hz AC excitation. This test would be a much more
stringent stressor of the voltage hold-off capabilities of the magnet
material. The peak 5.5 kV voltage across 2mm of laminate is equivalent
to \~20 kV/cm RMS. Figure 3.5-55 shows a chart[^6] of
rod(sharp-edged)-plane discharge tests of epoxy/fiberglass laminates. An
epoxy/fiberglass laminate of similar thickness (1.5mm) should survive
\~6 months of 50 Hz operation. In the lower chart (Figure 3.5-55), we
extrapolate the 1.5mm 20 deg.C curve to the left in the lower chart we
also find that the discharge inception voltage could be as little as 10%
of the applied voltage in order to survive the 60 hrs.

Given the very short duration of our pulse voltage (\< 20μsec) the
possible of a corona discharge and breakdown seems unlikely.

![](media/image64.png){width="5.996527777777778in"
height="7.477777777777778in"}

[]{#__RefHeading___Toc91568075 .anchor}Figure 3.5‑55: Rod-plane
insulation tests from Alston

Higher forces:

During the pulse, the septa have a magnetic pressure on them that is
directed outward from the core. A full sine current pulse will generate
two such outward pulses. The pressure against the thin septum is 0.64
bar \@0.4T, for the thick septum 7.0 bar @ 1.33T. The thin septum is 1mm
thick and the maximum stress associated with this pressure is +/- 3500
psi (27.8 Mpa); this is primarily a bending stress. The thick septum is
6.4 mm thick but has a section on one end of 3.2 mm thick; maximum
stress here is +/- 4400psi (33.3 Mpa). A typical fatigue endurance limit
stress for 1100 Copper alloy is 10 ksi (69Mpa) (for 10^7^ cycles), so
there is a factor of safety of over two on fatigue.

Increased heat loading:

In the thick septum original operating design, the nominal 1.0T gap
field 100 microsec half sine pulse produces 35 J/pulse Joule loss in the
coil. For top-off the pulse will be a full sine 1.33T gap field of 250
microsec duration. Joule losses in the coil rise to 155J/pulse, or 155
Watts \@1 Hz pulse rate. At present the coil is conductively cooled to
the core to which it ostensibly remains bonded to. Magnetic forces tend
to push the conductors towards the back leg of the core, however
potential debonding of the coil from the core cannot be discounted. For
this reason forced air or water cooling will be used on the thick
septum. A water flow rate of 0.12GPM is indicated to keep coil temp rise
below 5 deg. C. The cooling channel is 4mm dia.; such a flow rate will
have negligible pressure drop. Due to the high voltage, water
conductivity may need to be higher than the ALS LCW supply; if so a
dedicated system will be supplied for these magnets. Coil losses are
much less in the thin septum coil (0.44W@ 0.4T, 1 Hz) and this magnet
will remain conductively cooled.

Septum heating: Joule heating indicates negligible temperature rise in
the septums for continuous pulsing at 1 Hz. For the thick septum a Joule
heating of 11 W/m produces a 20mKdeg steady state temp rise between the
horizontal midplane of the septum and the bulk of the shield. For the
thin septum a Joule heating of 0.26 W/m gives a steady state temp rise
of 1.3 mK between the horizontal midplane of the septum and the bulk of
the beamtube.

Core heating: From a chart of core loss as a function of high frequency
AC B field excitation, core total losses in the thick septum are 40W for
full sine (250 microsec) operation @ 1.33T 1 Hz pulse rate, up from 8W
at 1.0T half sine 100 microsec operation@ 1 Hz as originally calculated.

The magnet is cooled conductively to ambient temperature of the vacuum
box through the three aluminum pads of the baseplate which the magnets
sit on, and are bolted down to. The actual contact pressure and fit are
unknown so, assuming a thin 0.003" layer of air is present between the
magnet and these feet (which would then be the dominant thermal
resistance), a maximum possible temperature rise of 3.5 deg. K is
indicated. In reality the fit is likely to be better and temp rise may
be much lower than this.

Radiation damage to the Epoxy binder:

This has not been assessed but is not expected to be a problem, since
the radiation dose for all existing equipment is not expected to
increase with the addition of a collimation/scraper system to localize
losses away from sensitive equipment.

#### Contingency plans and modifications septa magnets:

We've attempted to assess the key factors that could lead to an
accelerated failure of the septa pulse magnets. The assessments are
speculative at best and given the critical dependence of the ALS on
proper septum magnet function, we are preparing a detailed mechanical
procedure for the rapid change out of any of the septa magnets with
'machine ready' spares. The spares were upgraded to a 'machine ready'
condition during R&D phase of this CDR. The plan will identify the
diagnostic equipment and procedures needed to quickly determine the
fault condition after replacement with a the machine spare.

Replacement of any of the septa magnets with a spare is procedurally
complex and labor intensive. In particular the replacement of the SR
thin septa is the most difficult. Given the exigencies of machine 'down
time' this procedure will also attempt quantify the maximum time
required to replace the SR thin septa with it's requisite spare. We have
been advised that the canonical maximum down time for unscheduled
machine operations is one week. After careful analysis it is hoped that
we will be able to meet this time limit.

Electronic 'windowing' circuitry will be added to sense any significant
changes in a magnets current waveform. A progressive insulation failure
i.e. a turn-to-turn or turn-to-ground short can be quickly sensed and
stopped in one cycle. Given the relatively low stored energy in these
magnets it is fairly likely that coil may be saved from significant
damage and will be repairable 'on the core". This would save many
man-months of effort needed to procure conductor and insulation, and to
re-commission the coil winding and potting apparatus.

For example the damage caused by an electrical failure at the sharp
core-conductor edge as discussed above may be repaired without winding
another coil. The insulation can be removed by hand in the breakdown
area by judicious hand filing and a small half round stainless steel
"field smoothing piece" can be electrically bonded to the core at the
corner thus reducing the local field concentration. The repaired area
would be vacuum repotted with fiberglass and epoxy.

Another concern is core delamination in the thick septa magnets. Our
stress calculations suggest this an unlikely event but the magnet shield
box end plates could be easily modified to accommodate the addition of
longitudinal core compression plates (actuated by springs or bolts) that
would limit or otherwise negate the effect of delamination. Delamination
caused by accelerated damage to the epoxy from synchrotron radiation has
not been assessed.

#### Parameter measurement plan: 

As discussed in 'contingency plan and modifications' section above the
thin and thick septum spares have been upgraded to a 'machine ready'
condition. The spare storage ring beam tube has been located and
fastened to the gap face of the thin septum magnet. Both magnets have
been mounted on a granite table and will be driven by a new higher
voltage spare driver that has already been constructed for testing the
magnets and as a ready spare for the existing septa pulse magnets.

The key measurements will include stress and heating tests, magnetic
field measurements in the gap and adjacent beam tube, and short life
tests. The stress and heating tests will include a coil-to-ground high
voltage (Hi-pot) test, corona breakdown signatures, local conductor
heating at nominal power and repetition rate, calorimeter measurements
at nominal operation, constant voltage vs. current test to measure total
head load, and sonic spectra measurements with attached accelerometer.
The magnetic field measurement will be made using a 'electrically
isolated' long longitudinal Bdot probes and compared against point
measurements made with ad hoc broadband Hall probes manufactured by
SENSIS GmbH. The short life tests will include operating the magnets at
an accelerated pulse rate at nominal 1.95 Gev field parameters for \~1%
of their 10 year lifetime or 10.8\*10^4^ shots.

#### Further critical studies to do: 

As discussed in Table 3.5-13 the SR thin septum magnet is presently
overdriven by 20%. Operation at 2.0 GeV will increase the overdrive
condition to \~50%. The reasons for the overdrive condition are not
understood at this time. A beam injection analysis could be performed to
determine if the angle and position into the thick septum could be
incorrect. As a result the thin septum is driven harder to correct for
this condition. It has been noted that the booster to storage ring
transfer line has never been surveyed.

#### Summary of study: 

Our theoretical and empirical results indicate that the existing BR/SR
thick and thin septa will have the desired field quality for operation
at 2.0 GeV operation. Modification of the SR thick septum driver to a
'full ring' mode will bring the amplitude of the septum leakage field
within acceptable limits. High μ laminated shielding will further
improve the leakage fields. Estimates of possible failure modes caused
by the increased operational stresses suggest that the probability of a
magnet failure is relatively low. To mitigate the stresses we plan to
add water or air-cooling of both magnets.

However we will have two 'ready spare' magnets which will be life tested
and coupled with a well defined magnet swap-out plan that should cover
the most likely failure contingencies. Further investigations of the
thin septum overdrive need to be made.

### Storage ring 'fast' bump magnets

Two microseconds before the beam is transferred from the booster to the
storage ring a set of four 'fast' dipole magnets are energized to
produce a four-turn local closed-orbit distortion in the stored beam.
The location of the Bump Magnets in the storage ring is shown in Figure
3.5-34. (Storage Ring injection area) and are labeled as SR01S_BUMP1 to
BUMP4. Each of the four bump magnets is identical and their design and
construction very similar to the booster ring 'fast' kicker magnets.
Larger than the kicker magnets they are single-turn ferrite loaded
(MN8CX) window frame magnets designed to easily accept a sinusoidal
current waveform of several kilo amperes peak and a half sine period of
four microseconds.

#### Existing driver design:

Great care was taken to minimize any potential offset in the beam closed
orbit during the injection cycle. Precise magnetic field correspondence
between the two magnet groups was accomplished through the precise
construction of each magnet and the series-parallel connection of the
magnet to the discharge modules. In addition the 'downstream' set of
magnet have an additional 5.3 ft of cable to make up for the electron
'time of flight' between the two magnet groups.

The sinusoidal current wave form is generated by the resonant discharge
of a low inductance capacitor bank through an SCR switch array into the
predominantly inductive four bump magnetic load. The bump magnets are
connected by a very low inductance transmission network to four parallel
bipolar SCR-capacitor discharge modules. The basic topology of a
discharge module is shown in Figure 3.5-56. Each module has sixteen high
voltage SCRs (eight + and eight -) which are charged by opposite
polarity high voltage (10 KV max) power supplies. There are four
discharge modules which gives a total of sixty four SCRs in the pulse
chassis. The series parallel lattice of SCR's is necessary to
accommodate the high standoff voltages and provide the high di/dt
capability required to survive a 7000 kA, 4 us pulse. The current system
has been in operation since 1992.

![](media/image65.wmf)

[]{#__RefHeading___Toc91568076 .anchor}Figure 3.5‑56: One of four
bipolar switch modules

#### 

#### Topoff upgrade issues, experiments and results:

Mechanical offset of injection septa magnets:

Operational measurements have demonstrated that the bump driver system
cannot quite reach the required orbit offset for optimal beam injection.
Since the driver power supplies are at or near their voltage limits a
simple solution has been the addition of slight (1 -- 2 mm) orbit
correction of the stored beam towards the injection septa during the
normal injection process. During our Top-off investigations it was
realized that the entire injection vacuum assembly could be moved
laterally +/- 10mm. This capability has offered two advantages:

1)  The injection orbit correction can be permanently removed.

2)  Bump drivers and magnets do not have to be redesigned for 1.9 Gev
    injection.

Several machine experiments have successfully demonstrated both
capabilities.

Vertical and horizontal kicks caused by the injection bumps:

Great care was taken to minimize any potential offsets in the beam
closed-orbit but some observable problems still exist. Based on prior
beam measurements the amount of stored beam distortion when the bump
magnets are operating is presently acceptable for users. It does
suggests further investigation for future Topoff beam stability
improvements. These observed problems suggest some future experiments
and system upgrades.

1)  An observed \>100um vertical kick during bump operation may be
    caused by systematic magnet misalignments.

    a.  This problem may be correctable by re-alignment of the bump
        magnets.

2)  An observed horizontal kick of similar magnitude during bump
    operation may be due to inductive mismatch between the 'upstream'
    and 'downstream' magnet groups. This kick may be caused by the
    missing 'backend' compensation coil

    a.  The compensation coil should be reinstalled to confirm this
        theory

3)  Both vertical and horizontal kicks could be greatly reduced by the
    construction of closely matched individual solid state drivers for
    each bump magnet.

Summary:

Successful experimental results have shown that storage ring driver and
bump magnets do not need to be upgraded for 'top-off' operation. However
there are transient orbit distortions caused by the SR bump system that
may be correctible through magnet realignments or hardware
modifications.

### Summary of pulse magnets study: 

Our measurement results have shown that for 2.0 GeV operation the
booster ring bumps reach the nominal B fields with sufficient headroom.
Higher field measurements indicate some nonlinear effects in the
measurements but this is well above the nominal operating point.
Conversion to water cooling is not necessary. We recommend that the
capacitors in all thee pulse drivers be replace for the upgrade and if
necessary the charging supplies be replace with modern commercially
available models**.**

Modeling and calculations have shown that the existing magnets in the
Booster fast extraction kicker are adequate for 2.0 GeV. Additionally
the kicker magnet drivers can be easily modified to operation with the
higher voltage requirements as discussed in the booster fast extraction
kicker summary.

Theoretical and empirical results indicate that the existing BR/SR thick
and thin septa will have the desired field quality for operation at 2.0
GeV. Modification of the SR thick septum driver to a 'full ring' mode
will bring the amplitude of the septum leakage field within acceptable
limits. High μ laminated shielding will further improve the leakage
fields. Estimates of possible failure modes caused by the increased
operational stresses suggest that the probability of a magnet failure is
relatively low. To mitigate the stresses we plan to add water or
air-cooling both magnets.

However we will have two 'ready spare' magnets which will be life tested
and coupled with a well defined magnet swap-out plan that should cover
the most likely failure contingencies. Further investigations of the
thin septum overdrive need to be made

Successful experimental results have shown that storage ring driver and
bump magnets do not need to be upgraded for 'topoff' operation. However
there are transient orbit distortions caused by the SR bump system that
may be correctible through magnet realignments or hardware
modifications.

## DC and Slow Ramped Magnets

To accommodate the goal of increasing the Booster Ring energy to 1.95
GeV, the various Booster Ring DC and ramped magnets and power supplies
must be incremented in current in approximate proportion to the energy
increase, 1.95/1.5 or about 30%.

These increases naturally put additional stresses on the existing
magnets, power supplies, DC wiring, and AC utilities. Fortunately, the
magnets themselves were designed with 1.95 GeV operation in mind, so
this section will address the power supply, and wiring issues.

It is desired to avoid the high costs of upgrading the AC utilities
serving the Booster Bend and QD/QF power supplies. Toward that goal, the
Booster cycle period will be extended from 1 second to 3 seconds. This
will reduce the ramping rate requirements for these magnets, thus
minimizing the increase of peak and average AC RMS currents over 1.5 GEV
values. The ramp will be a near linear triangular envelope that will
dwell at zero current for the last 20% of the period. The dwell at zero
reduces RMS heating in the AC and DC side wiring so that existing
cabling can continue to be used.

We are looking into the use of Switching Mode power supplies. Here, the
potential exists for further lowering the AC demands by discharging the
ramping magnets into a capacitor bank instead of pushing that energy
back into the AC line. This technique will significantly reduce the RMS
heating in the AC wiring and utility transformer as well as to soften
the impact on the utilities of pulsing this megawatt load.

### Power Supplies

+-------------+---------------+---------------+-------------+---------+
| Magnet      | Present       | Required      | Action      | Est.    |
| System      |               |               |             | Cost    |
+-------------+---------------+---------------+-------------+---------+
| B Bend 1 Hz | 1175V @ 800 A | 2065V @ 1050A | Must        | 450 k\$ |
|             |               |               | replace     |         |
| 0.5 Hz      |               | 1422V @ 1050A | with more   | 300 k\$ |
|             |               |               | powerful    |         |
| 0.33 Hz     |               | 1208V @ 1050A | unit.       |         |
+-------------+---------------+---------------+-------------+---------+
| QD          | 110V @ 265A   | 234V @ 520A   | Must        | 100 k\$ |
| Quadrupoles | Cont.         | Pk            | replace     |         |
|             |               |               | with more   |         |
| 1 Hz        | 270V @ 460A   |               | powerful    |         |
|             | Peak          |               | unit.       |         |
+-------------+---------------+---------------+-------------+---------+
| QF          | 110V @ 265A   | 287V @ 520A   | Must        | 100 k\$ |
| Quadrupoles | Cont.         | Pk            | replace     |         |
|             |               |               | with more   |         |
| 1 Hz        | 270V @ 460A   |               | powerful    |         |
|             | Peak          |               | unit.       |         |
+-------------+---------------+---------------+-------------+---------+
| S           | Not in use    | 45 V @ 10 A   | Must        | 5k\$/ea |
| Sextupoles  |               |               | replace     |         |
| (8)         |               |               | with more   |         |
|             |               |               | powerful    |         |
|             |               |               | unit.       |         |
+-------------+---------------+---------------+-------------+---------+
| BTS Bends   | 33V @ 820 A   | 47V @ 900A    | Must        | 5       |
| (4)         |               |               | replace     | 0k\$/ea |
|             |               |               | with more   |         |
|             |               |               | powerful    |         |
|             |               |               | unit.       |         |
+-------------+---------------+---------------+-------------+---------+
| BTS Quads   | 40V @ 130 A   | 36.6V @ 110A  | No action   | 0       |
| (9)         |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS         | 15V @ 50 A    | 15V @ 50A     | No action   | 0       |
| Q2.2/Q3.1   |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS HCM (9) | 30V @ 8 A     | 30V @ 8 A     | No action   | 0       |
|             |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS VCM (9) | 30V @ 8 A     | 30V @ 8 A     | No action   | 0       |
|             |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+

[]{#__RefHeading___Toc91568104 .anchor}Table 3.6‑14: List of all mayor
dc and ramped power supplies in the booster and BTS including upgrade
requirements.

List of some of the main features of the power supplies:

-   New power supplies will be switchmode systems with;

-   Increased efficiency over SCR systems.

-   Ethernet control.

-   14 bit resolution (16 bit for BTS PS's).

-   Arbitrary waveform generator (for ramping supplies).

-   0.05% repeatability (for ramping supplies).

-   300 ppm stability (for continuous supplies).

-   Capacitor bank for energy recovery (dipole).

-   Reduced I²R heating of 12 KV transformer & AC wiring.

-   Reduced 12 KV transformer mechanical stress.

-   Reduces peak AC current demand.

### DC Cabling

+-------------+---------------+---------------+-------------+---------+
| Magnet      | Present       | Required      | Action      | Est.    |
| System      |               |               |             | Cost    |
|             | Capacity      | (20% zero     |             |         |
|             |               | dwell)        |             |         |
+-------------+---------------+---------------+-------------+---------+
| B Bend      | 585 A RMS     | 542 A RMS     | No action   | 0       |
|             |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| QD          | 285 A RMS     | 268 A RMS     | No action   | 0       |
| Quadrupoles |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| QF          | 285 A RMS     | 268 A RMS     | No action   | 0       |
| Quadrupoles |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| S           | Not in use    | \-\-\-\--     | No action   | 0       |
| Sextupoles  |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS Bends   | 1000 A RMS    | 900 A RMS     | No action   | 0       |
| (4)         |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS Quads   | 150 A RMS     | 110 A RMS     | No action   | 0       |
| (9)         |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS         | 75 A RMS      | 50 A RMS      | No action   | 0       |
| Q2.2/Q3.1   |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS HCM     | 20 A RMS      | 8 A RMS       | No action   | 0       |
| (11)        |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS VCM     | 20 A RMS      | 8 A RMS       | No action   | 0       |
| (11)        |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+

[]{#__RefHeading___Toc91568105 .anchor}Table 3.6‑15: List of capability
of DC cables for all mayor booster and BTS power supplies.

### AC Power

+-------------+---------------+---------------+-------------+---------+
| Magnet      | Present       | Required      | Action      | Est.    |
| System      |               |               |             | Cost    |
|             | Capacity      | (40% Duty     |             |         |
|             |               | Cycle)        |             |         |
|             |               |               |             |         |
|             |               | 1 Hz. 85%     |             |         |
|             |               | Eff.          |             |         |
+-------------+---------------+---------------+-------------+---------+
| B Bend      | 800 A RMS     | 772 A RMS     | No action   | 0       |
|             |               |               | required    |         |
|             |               | (0.5 Hz)      |             |         |
+-------------+---------------+---------------+-------------+---------+
| QD          | 125 A RMS     | 109 A RMS     | No action   | 0       |
| Quadrupoles |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| QF          | 125 A RMS     | 89 A RMS      | No action   | 0       |
| Quadrupoles |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| S           | 10 A RMS      | 5 A RMS       | No action   | 0       |
| Sextupoles  |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS Bends   | 125 A RMS     | 60 A RMS      | No action   | 0       |
| (4)         |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS Quads   | 20 A RMS      | 14 A RMS      | No action   | 0       |
| (9)         |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS         | 20 A RMS      | 7 A RMS       | No action   | 0       |
| Q2.2/Q3.1   |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS HCM     | 10 A RMS      | 5 A RMS       | No action   | 0       |
| (11)        |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+
| BTS VCM     | 10 A RMS      | 5 A RMS       | No action   | 0       |
| (11)        |               |               | required    |         |
+-------------+---------------+---------------+-------------+---------+

## Timing System

### Injector Timing

The ALS Timing System was designed to operate the Booster Ring at 1, 2,
5, and 10 PPS. The existing Rep-Rate module cannot be modified for the
anticipated rep-rates of 0.33, 0.5, and 1 PPS so a new module must be
designed and fabricated.

In current operation, the Booster Bend Magnets are allowed to ramp up at
their L/R time constant, the Timing System controls the duration of the
ramp by means of the Gauss Clock. Proposed operation will replace this
with a programmed ramp applied to the magnet power supply, however, the
Timing System will still be responsible for triggered the start of the
Bend, QD, and QF ramps. A new Magnet Control module must be designed and
fabricated to support this new mode of operation.

Various minor changes and adjustments to other Timing System modules may
be required to accommodate the increased periods and higher magnetic
field strength measurements.

### User Gating System

A new system is required to give Users advanced notice of an Injection
Cycle so that they can gate their data collection if necessary.
Notification would consist of:

a). A coarsely timed pulse significantly advanced from the injection
event.

b.) A more precisely timed pulse immediately prior to the event.

c.) A precisely timed gate that fully encloses the perturbed time space
with minimal overlap.

The system would be designed with a central chassis located at the
Timing System racks and satellite chassis located convenient to the
users. Signal distribution will be identical to the pre-existing User
Timing System with fiber optic trunk lines from the central chassis to
distribution chassis's as required. Each distribution chassis handles
wired distribution to the individual satellite chassis.

## Booster RF System

### Overall System Introduction & Description

The current ALS Booster RF system operates at 499.654 MHz and uses a
single room temperature re-entrant RF cavity identical to those used in
the ALS Storage Ring. A modified 15kW commercial UHF transmitter powers
the cavity. Tuning of the RF cavity is achieved by the movement of the
metallic cylinder, driven by a stepping motor, in or out of the cavity.
The Booster cycles at 1Hz, each cycle consisting of 350ms accelerating
ramp and 650ms recovery/quiescent period. Tuner control loop is enabled
only during quiescent period of the Booster cycle. In the current
injection scenario, the booster ring accepts three 50 MeV (8ns apart)
electron bunches from ALS drift tube traveling wave LINAC and
accelerates them to 1.5GeV. The Booster RF cavity cell power ramps from
80W at injection to 7kW at the end of the accelerating cycle. The
average ALS Booster beam current is 4mA (1nC total beam charge). This
value is also adequate for the required ALS Storage Ring beam current
uniformity for the Top-Off mode of operation. The schematic diagram of
the Booster Ring RF system is shown in Figure 3.8-57.

![](media/image66.jpeg){width="5.402083333333334in"
height="4.308333333333334in"}

[]{#__RefHeading___Toc91568077 .anchor}Figure 3.8‑57: Principal drawing
of Booster RF system.

#### Beam Loading Effect in the 50MeV ALS LINAC Structure

> In ALS Top-Off operation mode, to insure more uniform storage ring
> beam fill pattern, the injector might deliver up to 10 bunches in each
> injection cycle. What impact will this have on the LINAC output beam
> energy spread?
>
> The ALS LINAC has uniform parameters along its length (constant
> impedance structure). The fill time for a constant impedance structure
> is given by:
>
> $T_{f} = \frac{L}{v_{g}} = \tau \cdot \left( \frac{2 \cdot Q}{\omega} \right)$
> = 393ns **(3.8‑3)**
>
> where:
>
> L - length of single linac section (2m)
>
> v~g~ - energy group flow velocity
>
> τ - attenuation parameter (0.285 per 2m section)
>
> Q - linac structure quality factor (Q=13000)
>
> ω - angular operational frequency (ω=2\*π\*2.998GHz)
>
> Since the filing time of the linac accelerating structure is much
> longer than the bunch spacing (393ns\>\>8ns), the beam can be
> represented as a DC pulse with its width equal to the length of the
> pulse train when determining the beam-cavity interaction. The formula
> for the beam-induced voltage in a traveling wave LINAC structure as
> developed by P.B. Wilson \[28\] is:
>
> $V_{b}(x) = I_{0} \cdot r_{\text{sh}} \cdot L\left\lbrack \left( 1 - \frac{1}{\tau} \right) \cdot \left( 1 - e^{- \tau \cdot x} \right) + x \cdot e^{- \tau \cdot x} \right\rbrack$
> (3.8‑4)

where:

> x -bunch length parameter: x=t/T~f~ (t- length of the bunch train)
>
> V~b~(x) -beam induced voltage
>
> I~0~ -linac beam current
>
> r~sh~ -linac shunt impedance (53MΩ/m)
>
> L -length of single LINAC section (2m)
>
> The beam-induced voltages were calculated for the two cases listed
> below:
>
> 1\. Current multibunch operation mode: 3 bunches; total charge per
> injection cycle Q~tot~=1e^-9^\[C\]; Io=62.5\[mA\]; t=16\[ns\];
> x=0.041; τ\*x=0.0117
>
> 2\. Proposed multibunch mode for top-off operation: ten bunches total
> charge per injection cycle-Q~tot~=1e^-9^\[C\]; Io=13.9\[mA\];
> t=72\[ns\]; x=0.183; τ\*x=0.0522
>
> The results are as follows (for entire LINAC -2 sections):
>
> Case #1, V~b~=150kV energy spread: σE/E= 0.3%
>
> Case #2 V~b~=136kV energy spread: σE/E= 0.27%
>
> The conclusion reached is that the beam loading effect in ALS LINAC
> injector is not a significant problem for the proposed top-off mode of
> operation. No compensation is required for the proposed ALS main ring
> injection rate. The energy spread for 10-bunch LINAC operation is 10%
> lower than for 3-bunch operation, for the same total beam charge.

#### Beam Loading Effect in the Booster Ring.

Beam loading effect during beam injection from ALS LINAC into the
Booster can cause a fast (at the rate of the cavity's time constant)
cavity voltage amplitude and phase change and as an effect, this can
lead to significant beam losses.

Beam loading effect in the booster ring could be corrected by:

-   initial detuning of the RF cavity prior to the beam injection moment

-   increasing the power source-to-RF cavity coupling coefficient (more
    power from RF source required)

-   increasing the RF cavity voltage during beam injection (results in
    larger synchrotron tune changes that may lead to a synchrobetatron
    resonance problem).

#### Synchrobetatron Oscillations in ALS Booster Ring.

Coupling between transverse and longitudinal oscillations gives rise to
excitation of resonances for tunes, which satisfy the following
equation:

$k \cdot Q_{x} + l \cdot Q_{y} + m \cdot Q_{s} = n$ (3.8‑5)

where Q~x~, Q~y~ and Q~s~ are horizontal, vertical and synchrotron tune
values and k, l, m and n are integers.

For the given lattice parameters horizontal and vertical tunes are
constant (for ALS booster ring Q~x~=5.82 and Q~y~=2.72). From a logical
point of view, the simplest way to avoid the synchrobetatron resonances
problem is to choose the optimum Booster Ring operation conditions,
which includes maintaining the synchrotron tune value constant over
entire Booster energy ramp. This can be done by maintaining a constant
ratio of beam energy to cavity voltage.

### Booster RF Power Requirements for Top-Off Mode of Operation 

In Top-Off mode of operation, the Booster RF system has to accelerate
the electron beam up to the full ALS Storage Ring energy (1.9GeV). The
dominant mechanism, which dictates the minimum required RF bucket height
is the quantum emission of energetic photons by the electron beam
(quantum lifetime). The quantum lifetime τ~q~ is a steep function of the
electron beam energy and according to Sands \[29\] and \[30\] is given
by:

> $\tau_{q} = \frac{\tau_{e}}{\eta_{\sigma}^{2}}\text{exp}(\frac{\eta_{\sigma}^{2}}{2})$
> **\[3.8‑4\]**
>
> where:
>
> τ~q~-quantum lifetime
>
> τ~e~-longitudinal damping time
>
> $\eta_{\sigma} = \frac{\text{relative} \cdot \text{bucket}\text{.}(\text{half}) \cdot \text{height}}{\text{relative} \cdot \text{energy} \cdot \text{spread}}$
> \[3.8‑5\]

Table 3.8-16 shows the quantum lifetime, synchrotron tune, cavity cell
power and effective ALS Booster cavity voltage (for cavity shunt
impedance R~sh~=5MΩ) as a function of η~σ~ parameter for 1.9GeV electron
beam energy.

+-------+--------------+--------------+--------------+--------------+
| η~σ~  | Quantum      | Synchrotron  | Cavity Cell  | Cavity       |
|       |              |              |              | Voltage      |
|       | Lifetime     | Tune         | Power        |              |
+-------+--------------+--------------+--------------+--------------+
| \-    | \[s\]        | \-           | \[kW\]       | \[kV\]       |
+-------+--------------+--------------+--------------+--------------+
| 3     | 0.017        | 0.0120       | 19.0         | 436          |
+-------+--------------+--------------+--------------+--------------+
| 3.5   | 0.065        | 0.0129       | 22.8         | 477          |
+-------+--------------+--------------+--------------+--------------+
| 4     | 0.319        | 0.0137       | 27.3         | 522          |
+-------+--------------+--------------+--------------+--------------+
| 4.5   | 2.14         | 0.0146       | 32.8         | 573          |
+-------+--------------+--------------+--------------+--------------+
| 5     | 18.8         | 0.0155       | 39.3         | 627          |
+-------+--------------+--------------+--------------+--------------+
| 5.5   | 216.2        | 0.0164       | 47.0         | 686          |
+-------+--------------+--------------+--------------+--------------+
| 6     | 3203         | 0.0172       | 56.0         | 748          |
+-------+--------------+--------------+--------------+--------------+
| 6.5   | 61373        | 0.0181       | 66.5         | 815          |
+-------+--------------+--------------+--------------+--------------+
| 7     | 1600000      | 0.019        | 78.9         | 888          |
+-------+--------------+--------------+--------------+--------------+

[]{#__RefHeading___Toc91568106 .anchor}Table 3.8‑16: ALS Booster RF
parameters as a function of η~σ~ parameter.

Booster RF parameters for proposed ramp (constant synchrotron tune
value) are presented in Table 3.8-17. Calculations were done for 4mA
(1nC total beam charge) booster current, cavity-to-power source coupling
factor β~c~=2 (cavity tune into the resonance prior to beam injection
moment).

+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| B   | S   | RF  | Cav | Stati | Dy    | C     | Cavity   | Synch  |
| eam | ync | C   | ity | onary | namic | avity | Voltage  | rotron |
|     | hr. | ell |     |       |       |       |          |        |
| Ene |     |     | V   | B     | B     | Det   | (detuned | Rad    |
| rgy | T   | Po  | olt | ucket | ucket | uning | by beam) | iation |
|     | une | wer | age | Half  | Half  |       |          |        |
|     |     |     |     | H     | H     | (by   |          | losses |
|     |     |     |     | eight | eight | beam  |          |        |
|     |     |     |     |       |       | )     |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| MeV | \-  | kW  | kV  | keV   | keV   | deg   | keV      | keV    |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 50  | 0.0 | 0.  | 2   | 382   | 340   | -29.8 | 20.2     | 0.     |
|     | 181 | 054 | 3.2 |       |       |       |          | 000133 |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 100 | 0.0 | 0.  | 4   | 723   | 689   | -17.7 | 39.9     | 0.0021 |
|     | 181 | 175 | 1.8 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 200 | 0.0 | 0   | 8   | 1430  | 1403  | -9.3  | 80.8     | 0.034  |
|     | 181 | .67 | 1.9 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 300 | 0.0 | 1.5 | 12  | 2142  | 2116  | -6.2  | 121.8    | 0.172  |
|     | 181 |     | 2.5 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 400 | 0.0 | 2.6 | 16  | 2838  | 2808  | -4.7  | 160.7    | 0.544  |
|     | 181 |     | 1.2 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 500 | 0.0 | 4.1 | 20  | 3556  | 3516  | -3.8  | 202.1    | 1.33   |
|     | 181 |     | 2.5 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 600 | 0.0 | 5.9 | 24  | 4266  | 4208  | -3.1  | 242.5    | 2.76   |
|     | 181 |     | 2.9 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 700 | 0.0 | 8.0 | 28  | 4792  | 4882  | -2.7  | 282.5    | 5.1    |
|     | 181 |     | 2.8 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 800 | 0.0 | 1   | 32  | 5690  | 5550  | -2.3  | 323.8    | 8.7    |
|     | 181 | 0.5 | 4.0 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 900 | 0.0 | 1   | 36  | 6402  | 6190  | -2.1  | 364.5    | 14.0   |
|     | 181 | 3.3 | 4.7 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 1   | 0.0 | 1   | 40  | 7090  | 6775  | -1.9  | 402.3    | 21.3   |
| 000 | 181 | 6.2 | 2.5 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 1   | 0.0 | 1   | 44  | 7808  | 7356  | -1.7  | 443.7    | 31.2   |
| 100 | 181 | 9.7 | 3.9 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 1   | 0.0 | 2   | 48  | 8550  | 7919  | -1.6  | 487.7    | 44.1   |
| 200 | 181 | 3.8 | 7.9 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 1   | 0.0 | 2   | 52  | 9243  | 8378  | -1.4  | 526.1    | 60.8   |
| 300 | 181 | 7.7 | 6.3 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 1   | 0.0 | 3   | 56  | 9976  | 8818  | -1.3  | 569.1    | 81.7   |
| 400 | 181 | 2.4 | 9.2 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 1   | 0.0 | 3   | 61  | 10710 | 9189  | -1.2  | 612.2    | 107.7  |
| 500 | 181 | 7.5 | 2.4 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 1   | 0.0 | 4   | 66  | 11512 | 9558  | -1.1  | 663.2    | 139.5  |
| 600 | 181 | 4.0 | 3.3 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 1   | 0.0 | 5   | 70  | 12252 | 9759  | -1.0  | 707.0    | 177.7  |
| 700 | 181 | 0.0 | 7.1 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 1   | 0.0 | 5   | 76  | 13084 | 9968  | -1.0  | 761.5    | 233.4  |
| 800 | 181 | 8.0 | 1.6 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+
| 1   | 0.0 | 6   | 81  | 13884 | 10018 | -0.9  | 812.3    | 277.3  |
| 900 | 181 | 6.0 | 2.4 |       |       |       |          |        |
+-----+-----+-----+-----+-------+-------+-------+----------+--------+

[]{#__RefHeading___Toc91568107 .anchor}Table 3.8‑17: Booster RF
parameters for proposed energy ramp for ALS Top-Off mode of operation.

The stationary and dynamic 1.9 GeV ALS Booster RF buckets for 66 kW
cavity cell power and the single bunch with the population of 1000
electrons and the normal energy distribution are shown in Figure 3.8-58.
Figure 3.8-59 shows 10 LINAC bunches with the total energy spread of
136keV captured by 54W Booster RF bucket at injection (the energy spread
inside each LINAC microbunch is neglected). The difference between the
static and dynamic buckets in this case is the result of the cavity
detuning due to the beam loading effect.

![](media/image67.png){width="3.920138888888889in"
height="3.6326388888888888in"}

[]{#__RefHeading___Toc91568078 .anchor}Figure 3.8‑58: RF buckets and
particle distribution in ALS Booster at 1.9 GeV.

[]{#__RefHeading___Toc91568079 .anchor}Figure
3.8‑![](media/image68.jpeg){width="3.9298611111111112in"
height="3.7104166666666667in"}: RF buckets and 10 injected linac bunches
into ALS Booster at 50 MeV.

Table 3.8-18 shows the current and proposed Booster Ring RF Parameters.

  --------------------------------------------- ------------ -------------
  Parameter                                     Current      Proposed

  Frequency (MHz)                               499.64       499.64

  Harmonic number                               125          125

  Peak effective voltage (kV)                   300          813

  Beam current, multibunch mode (mA)            4            4

  Synchrotron radiation loss, dipoles (kW)      2            5

  Total effective shunt impedance, ZT2 (MΩ)     5            5

  Fundamental-mode cavity dissipation (kW)      7.8          66

  Waveguide and other losses (kW)               1            11

  Total RF power required (kW)                  8.8          77

  Total RF power installed (kW)                 22           80
  --------------------------------------------- ------------ -------------

[]{#__RefHeading___Toc91568108 .anchor}Table 3.8‑18: RF parameters for
current and Top-Off mode.

### Final Amplifier/Transmitter with Controller

It has been determined, as noted above, that the existing final
amplifier --transmitter can not produce the output power needed, so we
plan to replace it with a higher output power final
amplifier-transmitter based on an inductive output tube (IOT). We came
to this conclusion after first exploring two possible upgrade paths for
the existing transmitter. First we looked at replacing the existing
klystron with a higher power klystron. However the poor efficiency of
the larger klystron and the maintenance of an aging electro-mechanical
transmitter system dissuaded us from this option. Second we looked at
replacing the klystron with a higher power IOT. However, with this
option we were faced with installing a crowbar system and with
considerable rework of the existing transmitter's power supplies, relay
controls and interlocks during an ambitious installation shutdown
period. Additionally the maintenance of an aging electro-mechanical
transmitter system dissuaded us from this option.

In the end we opted to replace the final amplifier-transmitter, which
will be IOT based and have an integrated class A solid state drive
amplifier, integrated thyratron crowbar system, fiber optic isolated
metering, and an integrated microprocessor based control system. The
maximum output power is 80 kW CW. This higher output gives us sufficient
operating headroom above the required power level to ensure reliable
operation for all three modes (50 MeV to 1.5 GeV @ 1 Hz, 50 MeV to 1.9
GeV @ 0.5 Hz, and 77 kW CW). The higher operating efficiency (\>70%
expected) will pay back the initial capital cost difference, as compared
to a klystron upgrade, in a 3-4 year time frame.

### High Voltage Power Supply

The current high voltage power supply (HVPS) is rated at 22 kV @ 2.4 A
DC. It is a dry type, (no oil) air-cooled unit located inside of Bldg. 6
under the old dome section. We looked at three HVPS types as possible
replacement candidates; a Pulse Step Modulator (PSM), a SCR input
controlled 6-pulse rectifier power supply cooled by oil, or a SCR input
controlled 6-pulse rectifier power supply cooled by air. We felt the PSM
design though capable added a considerable amount of complexity to the
overall transmitter system, an amount of uncertainty with regard to
audio band noise injection and it put pressure on our budget due to its
higher cost. The oil cooled power supply would have been our next choice
because of its compactness but we are unable to introduce a significant
flammable source without greatly increased installation costs. Locating
an oil-filled power supply outside of Bldg. 6 was also looked at, but
without a dedicated wire-way we would have incurred considerable
installation costs and possible disruption of beamline operation in the
area during installation. Ultimately we chose the SCR input controlled
6-pulse rectifier power supply air-cooled version, which minimized the
fire hazard and installation costs.

The HVPS's maximum output will be 37 kV @ 4.0 A DC with a typical output
of 36 kV @ 3.3 A DC for all modes of operation of the Booster RF System.
The HVPS will be fabricated in an all-metal enclosure with a step-start
contactor and a complete self-protecting interlock system. The HVPS will
have a Star Point SCR controller on its input and a capacitor tuned
specifically for the typical output load noted above, which will set the
power factor to ≥ 0.92.

### RF Cavity Window

The RF power delivered is to the cavity via an aperture-coupling
cylindrical window made of aluminum-oxide. This window must reliably
deliver the expected 60 kW of power needed by the cavity to satisfy the
quantum lifetime requirements without multipactor, arcing, or
overheating. LBNL has designed, fabricated, anti-multipactor coated with
titanium-nitride in-house, and power tested to 66kW (the maximum of our
RF teststand) several windows that operate in the storage ring at power
levels approaching 50 kW without beam. We plan to reuse this proven
design and build 2 new windows (one spare) for this upgrade project.

### RF Transmission Line

The existing transmission line is primarily 3 1/8" coaxial line
consisting of a mixture of types as rigid, clamp line, 3" air dielectric
Heliax, 3 1/8" to 6 1/8" adapters (for the existing 75 kW) circulator),
and WR1800 (for interfacing to the cavity). The current transmission
line is rated for 16.8 kW average, however since the upgraded system is
required to deliver a ramped power profile from \< 1kW up to 77 kW over
a 1/2 second ramp the average power (19.3 kW) will exceed the reliable
operating range for this 3 1/8" line therefore it needs to be replaced.
Additionally, the existing line will not support the 70kW CW
test/maintenance mode.

The new transmission line will be primarily 6 1/8" rigid coax but it
will contain 2 short sections of 4 1/16" rigid and clamp line coax. The
output of the IOT is 4 1/16" EIA transmission line with forward and
reverse power couplers. Upon exiting the transmitter cabinet the line
will transition to 6 1/8" line to a SPDT 6 1/8" coaxial switch. The
switch selects between an 80 kW CW 6 1/8" load or the Booster cavity.
Following the switch is a length of 6 1/8" line, which connects to the
existing 75 kW circulator. The circulator has an 80 kW CW 6 1/8" load on
one port with the cavity connected on the other port via 6 1/8" line and
adapter to WR1800. There is an existing bi-directional WR1800 coupler
located at the cavity to measure cavity forward and reverse power.

### Controls & Interlocks

The existing Control and Interlock chassis are typical single purpose
custom relay chassis that are expensive to modify and difficult to work
on. We will likely replace these chassis with an Ethernet capable
Programmable Logic Controller (PLC) rated Safety Integrity Level 3
(SIL3) with a local pc and monitor providing a local control station at
the equipment. The SIL3 rating is necessary for inclusion in the Booster
Ring Personnel Safety System. By installing this PLC system in addition
to the embedded microprocessor based system supplied with the
transmitter, we will be able to replace all but two Intelligent Local
Controllers (ILC), the now obsolete workhorse of the ALS Control System.
There are sufficient expansion capabilities to accommodate the channels
on the remaining two ILC's. The new PLC systems will interface to the
existing EPICS based control system via MODBUS over Ethernet. This will
allow us to leverage existing MODBUS code already in use at the ALS.

### Utilities

The replacement of the transmitter and HVPS sub-systems impacts the
480/120 VAC and LCW plants. There is sufficient installed capacity to
accommodate the upgrade. See Table 3.8-19 below for current and
projected capacities.

  ----------------- ---------------- --------- ------------------ ---------------- --------- ---------
                    **Current                                     **Proposed                 
                    Installation**                                Installation**             

  System            **120/208 VAC**  **480     **LCW (gpm)**      **120/208 VAC**  **480     **LCW
                                     VAC**                                         VAC**     (gpm)**

  **Transmitter**   **30A**          **-**     **32**             **-**            **225**   **25**

  **HVPS**          **-**            **80**    **-**              **-**                      **-**

  **Xmtr Test       **-**            **-**     **5**              **-**            **-**     **12**
  Load**                                                                                     

  **Circulator**    **-**            **-**     **[5]{.mark}**     **-**            **-**     **4**

  **Circulator      **-**            **-**     **[5]{.mark}**     **-**            **-**     **12**
  Load**                                                                                     

  **Cavity**        **-**            **-**     **[5]{.mark}**     **-**            **-**     **30**

  **Cavity Window** **-**            **-**     **[1.4]{.mark}**   **-**            **-**     **2.5**

  **Cavity Tuner**  **-**            **-**     **[0.8]{.mark}**   **-**            **-**     **1.5**
  ----------------- ---------------- --------- ------------------ ---------------- --------- ---------

[]{#__RefHeading___Toc91568109 .anchor}Table 3.8‑19: Electrical power
and LCW requirements for current installation and upgrade condition.

> Transmitter LCW Circuit Cavity LCW Circuit

The current transmitter LCW requirement is 37 gpm and the new
requirement is also 37 gpm. The current cavity LCW requirement is 7.2
gpm (the circulator, circulator load and cavity are in series) and the
new requirement is 50 gpm.

### Structure Core Drilling

The existing Booster Ring roof penetration accommodates the 3 1/8" coax
transmission line and two -- 1" hoses for cooling the circulator and its
load. The requirement for higher average power transmitted to the cavity
translates into a larger coax line as mentioned above. We will need to
re-drill the roof penetration to \~ 8" and we will also need to drill at
least one more new hole to fit the hoses supplying LCW to the circulator
and its load. The existing and any new holes will not centered over the
beam axis therefore satisfying the radiation safety engineer.
Additionally, an existing unused roof block hole directly centered over
the cavity will be filled with concrete to remove the direct line of
sight to the cavity.

### Spares

The components that can cause a significant down time if they fail are
the IOT, solid-state drive amplifier, RF cavity-coupling window, and
various PLC components. We will need to have these items in hand at the
beginning of our commissioning.

##  Diagnostics

### Booster Diagnostics

The diagnostics in the Booster will play a major role during the
commissioning and operation of the Booster in the top-off mode.
Injection efficiency together with short and long term stability of the
booster operation conditions are fundamental requirements for the proper
operation in this new mode.

At the present time, the booster is operated with sextupoles off and
without any orbit control. Long-term drifts are compensated by
readjustments by the operators. In top-off operation, tolerances for the
injection parameter fluctuations are much tighter requiring more
efficient diagnostics systems. Some examples, synchro-betatron resonance
control is required during the energy ramping, closed orbit and current
monitoring are necessary for preserving the injection efficiency, bunch
cleaning requires accurate control of tunes, chromaticities and orbit.

In the next paragraphs, a description of the proposed new tune
measurement system and of the refurbishing and/or upgrade for the orbit
system is presented as well as the description of the proposed bunch
cleaning system.

#### Orbit Monitoring System.

The Booster ring has 32 beam position monitors distributed along the
circumference. They are equipped with the original ALS electronics that
allows for both single and multi turn measurements. The all orbit system
has been rarely used for several years and requires significant
refurbishing.

The requirements for this system during the topoff operation can be
distinguished in two main phases. During the commissioning, single turn
or few turns measurements will be required. Being the larger of the
betatron tunes greater than 6, about 13-14 BPMs should be equipped with
single turn electronics. During topoff operation, in order to maintain
an efficient injection and bunch cleaning, a regular monitoring of the
orbit is also required. Again, about 13-14 BPMs equipped now with multi
turn electronics will be sufficient for the task.

For this topoff upgrade, we are proposing to refurbish the existing
electronics for the single turn measurement and to buy the electronics
for a reliable orbit monitoring during operation.

A high level application, similar to the one existing for the ALS
storage ring, should be developed for allowing an easy monitoring of the
orbit in the booster.

#### Bunch Cleaning System

*Introduction and system description.*

In the present operation of the ALS, about 4 weeks per year are
dedicated to the so-called "two-bunches mode of operation". In such a
special mode, only two diametrically opposite buckets, over the 328
available, are filled with relatively high current (\~ 30 mA/bunch). The
distance in time between these buckets (\~ 330 ns) is large enough to
allow for experiments with long relaxation time. The "two-bunches"
users' community is continuously growing and the scientific quality of
their work is of very high level, making a top priority maintaining the
quality of these runs even with the top-off operation.

In order to avoid contamination of the experimental data, it is
fundamental to have high levels of "bunch purity". In other words, it is
extremely important that undesired particles in the nominally empty
buckets are kept down to a level lower than \~ 0.01% relatively to the
particle number in the main two bunches. Several mechanisms, during the
injection process, can contribute in contaminating the filling pattern
in the storage ring and even when injection is tuned at its best, a
contamination level of the order of 0.1% can still happen. For this
reason, a bunch cleaning procedure is always required.

At the present time, the cleaning is performed in the storage ring after
every injection and energy ramping to 1.9 GeV. The beam impedance of the
ALS vacuum chamber induces betatron tune shift on current, so that the
small current parasitic bunches have a tune significantly different from
the one of the two high current main bunches. By exciting the beam at
the betatron frequency of the parasitic bunches, one can generate large
transverse oscillations of the undesired bunches with minor effects on
the main ones. The insertion of a scraper kills the oscillating
particles allowing for the cleaning. Unfortunately, the whole procedure
requires about 4 minutes and perturbs the main buckets making it
incompatible with top-off operation.

![](media/image69.jpeg){width="4.802083333333333in"
height="1.601388888888889in"}

[]{#__RefHeading___Toc91568080 .anchor}Figure 3.9‑60: Bunch cleaning
system schematics

A convenient solution consists in performing the cleaning in the booster
before injecting in the storage ring. A possible scheme \[31\] \[32\] is
based on the idea of resonantly exciting large transverse oscillations
in all the bunches except the ones you want to save. With reference to
Figure 3.9-60, two signals, a sinusoidal wave at the frequency of one of
the betatron sidebands and a square-like wave that switches polarity
synchronously with the transit of the bunches to be saved, are mixed
together. The resulting signal is still an excitation at the betatron
tune but with always zero amplitude at the passage of the "good"
bunches. The signal is then amplified and sent to a transverse kick for
the beam excitation. A scraper in the plane of the excitation will
increase the efficiency of the cleaning and reduce the power requirement
for the amplifier.

Cleaning in the Booster requires that no contamination happens when
injecting from the booster to the storage ring. The technique described
above is already in routine operation at Spring 8 \[33\] in Japan and
under final test at the ESRF \[34\] in France. Here at the ALS, we have
tested in the storage ring the complete cleaning procedure with
successful results.

Table 3.9-20 shows the system parameters for the ALS Booster. The
cleaning is tuned for the maximum efficiency at the beam energy of 300
MeV. The excitation in the vertical plane will be applied for few tens
of ms during the energy ramp around the energy of 300 MeV. Ideally,
chromaticity should be corrected to zero in order to avoid spread of
tunes with energy. A non-properly corrected chromaticity will require
more excitation power for maintaining the required oscillation amplitude
within the beam energy spread range.

[]{#__RefHeading___Toc91568110 .anchor}Table 3.9‑20: Cleaning system
parameters for the ALS Booster.

+--------------------------+--------+---------------------+-----------+
| Beam energy at cleaning  | 300    | Natural vertical    | \- 4.61   |
|                          | MeV    | chromaticity        |           |
+--------------------------+--------+---------------------+-----------+
| Booster revolution       | 250.2  | Operation vertical  | 0.0 ± 0.1 |
| period (*T*~0~)          | ns     | chromaticity        |           |
+--------------------------+--------+---------------------+-----------+
| RF frequency             | 500    | Vertical Tune       | 2.72      |
|                          | MHz    |                     |           |
+--------------------------+--------+---------------------+-----------+
| Harmonic number          | 125    | Vert. excitation    | \~ 1.12   |
|                          |        | frequency           | MHz       |
+--------------------------+--------+---------------------+-----------+
| Long. Damp. time @ 300   | \~ 400 | Max tune variation  | \~ 5 ×    |
| MeV                      | ms     | at ∆*E*/*E* = 0.5%  | 10^-4^    |
|                          |        | (∆*ν~y~*           |           |
+--------------------------+--------+---------------------+-----------+
| Transv. damp. time @ 300 | \~ 800 | Vertical kick angle | \~ 6.3    |
| MeV (*τ~d~*)             | ms     | (∆*θ*              | μrad      |
+--------------------------+--------+---------------------+-----------+
| Vertical beta function   | \~ 10  | Kicker type         | stripline |
| at scraper position      | m      |                     |           |
| (*β~Sc~*)                |        |                     |           |
+--------------------------+--------+---------------------+-----------+
| Vertical beta function   | \~ 10  | Kicker transverse   | \~ 9000   |
| at the kicker position   | m      | shunt impedance     |           |
| (*β~K~*)                 |        |                     | Ω         |
+--------------------------+--------+---------------------+-----------+
| Distance vertical        | 10 mm  | Amplifier power     | \~ 200 W  |
| scraper-reference orbit  |        | (*P*)               |           |
| (∆*y*)                   |        |                     |           |
+--------------------------+--------+---------------------+-----------+
| Energy spread at 300 MeV | \~1.7× | Amplifier bandwidth | \> 200    |
| (rms)                    | 10^-3^ |                     | MHz       |
|                          |        |                     |           |
| (assuming 1% rms linac   |        |                     |           |
| energy spread @ 50 MeV)  |        |                     |           |
+--------------------------+--------+---------------------+-----------+

The parameters in the table have been evaluated according to the
criteria presented in reference \[32\]. In particular, the following
expressions have been used (the symbols in the following equations are
defined in Table 3.9-20):

$\begin{array}{r}
 \\

\end{array}$
$\Delta y \simeq \frac{1}{2}\frac{\Delta\theta\frac{\tau_{d}}{T_{0}}\left( \beta_{K}\beta_{\text{Sc}} \right)^{1/2}}{\left\lbrack 1 + \left( 2\pi\frac{\tau_{d}}{T_{0}}{\Delta\nu}_{y} \right)^{2} \right\rbrack^{1/2}}\ $
(3.9‑6)

or, as in our case, where
$\tau_{d}/T_{0}\text{>>}1/\left( 2{\pi\Delta\nu}_{y} \right)$:

$\begin{array}{r}
 \\

\end{array}$
$\Delta y \simeq \frac{\Delta\theta\left( \beta_{K}\beta_{\text{Sc}} \right)^{1/2}}{4\pi\ {\Delta\nu}_{y}}\ $
(3.9‑7)

where $\Delta\theta = \text{eV}_{k}/E$, with *e* and *E* the electron
charge and energy respectively and *V~k~* is transverse kick voltage
given by:

$\begin{array}{r}
 \\

\end{array}$ $V_{k} = \sqrt{2\text{PR}_{}}$ (3.9‑8)

Here *P* is the power applied to the kicker and *R*~⊥~ is its transverse
shunt impedance. The amplifier bandwidth has been chosen in order to
clean out parasites contiguous to the main buckets (2 ns distance).

Equations (3.9-1) and (3.9-2) do not include the tune shift on amplitude
that the particles will experience for large oscillations. The resulting
additional tune spread would require extra excitation power for
maintaining the amplitude of the oscillation at the same level. In our
proposed scheme, the inclusion of a vertical scraper in the booster
allows, by setting properly *∆y*, to control such effects without
dramatically increase the power requirements for the amplifier. It is
worth reminding that the scraper position must trade between an
efficient cleaning and an efficient injection in the booster.

In the next paragraphs, the new systems required for the cleaning
implementation are described.

#### Kicker system

The kicker for booster bunch cleaning will be a copy of the storage ring
vertical transverse feedback system kicker. The kicker is a vertical
stripline pair with 30 cm long electrodes each subtending 120 deg of the
beam. Driven differentially, the transverse shunt impedance of the
kicker is given by:

$\begin{array}{r}
 \\

\end{array}$
$R_{} = 2Z_{L}\left( \frac{2g_{}\text{sin}\left( \text{kl} \right)}{\text{kd}} \right)^{2}$
(3.9‑9)

where *Z~L~* is the stripline characteristic impedance, *k* = *ω*/*c*,
*l* is the electrode length, *d* is the electrode diameter and
$g_{} = (4/\pi)\text{sin}\left( \text{ΔΦ}/2 \right)$ with ∆Φ the
electrode subtend angle. The values for these quantities for the ALS
kicker are shown in Table 3.9-21. Using such values, the calculated
shunt impedance at low frequencies for the ALS kicker is *R*~⊥~= 8938
ohms which compares favorably to bench measurements of about 10 kΩ.

[]{#__RefHeading___Toc91568111 .anchor}Table 3.9‑21: ALS-like stripline
kicker characteristics.

  -------------------------- --------- -------------------------- --------
  Electrode length (*l*)     30 \[cm\] Electrode diameter (*d*)   70
                                                                  \[mm\]

  Electrode subtend angle    120       Characteristic impedance   50 \[Ω\]
  (∆Φ)                       \[deg\]   (*Z~L~*)                   
  -------------------------- --------- -------------------------- --------

The azimuthal position of the vertical kicker in the ring must be as
close as possible to the central defocusing quadrupole of the cell (cell
symmetry point) where the vertical beta function has a local maximum.

The power amplifiers for driving the kicker will be identical to the
storage ring transverse feedback system amplifiers. They are 250 watt,
250 MHz instantaneous bandwidth RF power amplifiers.

Nominally, one would use two amplifiers to drive the electrodes
separately at opposite phases with a total available power of 500 watts.
Recently, a bunch cleaning experiment was performed in the ALS storage
ring at 1.9 GeV using the transverse feedback system amplifiers and
kickers. In this case, only one electrode was driven with one amplifier.
In such configuration the effective shunt impedance is about half that
given by Eq. (3.9-4) resulting in a $\sqrt{2}$ reduction in kick. In
this experiment, a 125 MHz sine wave modulated by a vertical betatron
tune line was used to clean every other bunch in the ring. For 100 watts
of drive power and nominal scraper depths, perfect bunch cleaning within
the approximate 1% resolution of our instrumentation was obtained. In
addition, the cleaning process was essentially instantaneous as opposed
to the present technique that takes several minutes.

Depending on the final position that the scraper in the Booster will
have during the top-off operation, it could be that the more economical
single electrode drive scheme will be adequate for cleaning in the
booster. The current plan is to buy and install two amplifiers for the
booster kicker but possibly operate only one of them reserving the other
as an online spare. A commercial arbitrary function generator for
general bunch cleaning will replace the 125 MHz sine wave used in the
experiment.

#### Vertical Scraper

A single blade vertical scraper, as the one presently installed in the
ALS storage ring, will be installed in the Booster as well. The
azimuthal position of the scraper in the ring must be as close as
possible to the central defocusing quadrupole of the cell (cell symmetry
point) where the vertical beta function has a local maximum.

#### Storage Ring Cleaning System Upgrade

In some particular conditions, a high purity injection alone could not
be sufficient. In fact, specifically if the dynamic aperture of the
storage ring is larger than the RF bucket size, diffusion of particles
from the main bunches to the near buckets could happen. In that case, a
periodic cleaning in the storage ring will be required as well. We
propose to include in the storage ring a cleaning system similar to the
one in the Booster, specially taking into account that most of the more
expensive system components are already present in existing subsystems
in the ring.

The system will be identical to the one in the Booster but using the
existing transverse feedback system amplifiers and kickers jointly with
the existing vertical scraper. An additional arbitrary function
generator is required.

#### Transverse Tune Measurement System.

The Booster tune measurement system will utilize the bunch-cleaning
kicker and power amplifiers for exciting the beam at chosen vertical
betatron tune frequencies. For horizontal coverage an additional
horizontal kicker will need to be fabricated and installed and an
additional power amplifier will need to be purchased. The measurement
itself will be performed with a fast broadband oscilloscope utilizing
FFT to obtain frequency spectrums.

The azimuthal position of the horizontal kicker in the ring must be as
close as possible to the last focusing quadrupole before the cell
symmetry point, where the horizontal beta function assumes a local
maximum.

### BTS Diagnostics

#### Injection chain beam transmission monitor.

In the existing configuration the ALS complex has several beam charge
monitors: the linac and the LTB transferline are equipped with three,
the Booster has two monitors, the BTS three and the Storage Ring has
one. Table 3.9-22 summarizes the situation.

We are proposing the development of a high level application that
collects all the charge information and presents them in a single window
for an easy at a glance control of the transmission efficiency along the
injection chain.

[]{#__RefHeading___Toc91568112 .anchor}Table 3.9‑22: Beam charge
monitors in the ALS complex.

  ---------- ---------------------- -------------------- --------------------
  **Name**   **Type**               **Location**         **Present control
                                                         status**

  BIM1       Resistive wall current Linac: downstream    Multiplexed to a
             monitor                electron gun         scope

  ICT1       Integrating current    LTB: Linac end       Not connected
             transformer                                 

  ICT2       Integrating current    LTB: before booster  Controlled
             transformer            injection septa      

  FCT1       Fast current           Booster ring         Multiplexed to a
             transformer                                 scope

  DCCT1      DCCT                   Booster ring         Controlled

  ICT3       Integrating current    BTS: downstream      Controlled
             transformer            Booster extraction   
                                    septa                

  BIM2       Resistive wall current BTS central part     Multiplexed to a
             monitor                                     scope

  ICT4       Integrating current    BTS: before storage  Controlled
             transformer            ring injection septa 

  DCCT2      DCCT                   Storage ring         Controlled
  ---------- ---------------------- -------------------- --------------------

From the last column of Table 3.9-22, one can see that 5 of the 9
monitors are already controlled and the FCT in the Booster is a fast
monitor for special measurements and does not need to be included in our
proposed application. So only 3 monitors (BIM1, ICT1 and BIM2) need
upgraded electronics allowing for their integration in the control
system.

#### Synchrotron Radiation Monitors

The two synchrotron radiation monitors in the BTS will allow for the
non-destructive and continuous monitoring of the beam in the final part
of the injection chain. The monitors will exploit the visible and part
of the infrared portions of the synchrotron radiation emitted in two
bending magnets among the four identical 20 deg dipoles present at the
BTS. The higher dispersion in the first point source, will allow for the
control of the energy variations in the beam extracted from the booster,
while the second point, in a lower dispersion region, will be more
suitable for beam emittance measurements. But the fundamental idea is
that a quick glance at the two monitors will give the complete
information about the status of the injector chain. A similar scheme is
already in operation at ESRF in Grenoble with quite satisfactory results
\[35\].

Figure 3.9-61 shows the optical functions and the beam sizes along the
BTS with the position of the two source points.

![](media/image70.jpeg){width="5.418055555555555in"
height="3.388888888888889in"}

[]{#__RefHeading___Toc91568081 .anchor}Figure 3.9‑61: BTS optical
function, beam sizes and SR source point positions.

Source Point 1 exploits an already existing port on the vacuum chamber
of the first bend B1 of the BTS, see Figure 3.9-62. At the present time,
the port is equipped with a TV system (fluorescent screen) and in the
new configuration, it will be sufficient to replace the existing screen
with a metallic mirror to bring the synchrotron radiation out of the
chamber.

The synchrotron radiation characteristics of the Source Point 1 are
given in Table 3.9-23.

![](media/image71.jpeg){width="3.5493055555555557in"
height="2.0145833333333334in"}![](media/image72.jpeg){width="2.4659722222222222in"
height="1.8625in"}

[]{#__RefHeading___Toc91568082 .anchor}Figure 3.9‑62: Synchrotron
radiation monitor at BTS bend B1.

[]{#__RefHeading___Toc91568113 .anchor}Table 3.9‑23: Source Point 1
synchrotron radiation characteristics

+--------------------------+----------+-----------------------+------+
| Photons per beam passage | \~       | Horizontal acceptance | \~   |
|                          | 1        |                       | 18   |
| (between 250 -- 700 nm)  | .3×10^8^ | (total chamber        |      |
|                          |          | aperture)             | \[mr |
|                          |          |                       | ad\] |
+--------------------------+----------+-----------------------+------+
| Energy deposited in the  | \~ 8.0   | Minimum vertical      | 10   |
| mirror per passage       | ×10^-7^  | acceptance (total)    |      |
| (whole SR spectrum)      |          |                       | \[mr |
|                          | \[J\]    |                       | ad\] |
+--------------------------+----------+-----------------------+------+
| Bunch charge             | 9.84     | Mirror angle          | 45   |
|                          | ×10^-10^ |                       |      |
| (1.5 mA in the Storage   |          |                       | \[d  |
| Ring)                    | \[C\]    |                       | eg\] |
+--------------------------+----------+-----------------------+------+

Source Point 2 will be located downstream bend B3 of the BTS. In this
case, a new vacuum chamber segment will allow extracting the synchrotron
radiation, see Figure 3.9-63 and Figure 3.9-64. The linear actuator
shown in Figure Figure 3.9-63 is not strictly required but its presence
will allow positioning the mirror at the proper distance from the actual
electron beam orbit.

The synchrotron radiation characteristics of the Source Point 2 are
given in Table 3.9-24.

![](media/image73.jpeg){width="3.097916666666667in" height="2.25in"}

[]{#__RefHeading___Toc91568083 .anchor}Figure 3.9‑63: Synchrotron
radiation monitor at BTS bend B3 and detail of the mirror area. For the
symbols in the figure see Table 3.9-24.

[]{#__RefHeading___Toc91568114 .anchor}Table 3.9‑24: Source Point 2
synchrotron radiation characteristics

+-----------------------+---------+--------------------------+--------+
| Photons per beam      | \~      | Distance mirror-B3       | 10     |
| passage               | 6.      | vacuum chamber flange    |        |
|                       | 8×10^8^ | (D)                      | \[cm\] |
| (between 250 -- 700   |         |                          |        |
| nm)                   |         |                          |        |
+-----------------------+---------+--------------------------+--------+
| Energy per shot       | \~ 4.0  | Mirror projected         | 35     |
|                       | ×10^-6^ | horizontal size (Hp)     |        |
| (whole SR spectrum)   |         |                          | \[mm\] |
|                       | \[J\]   |                          |        |
+-----------------------+---------+--------------------------+--------+
| Bunch charge          | 9.84    | Mirror minimum vertical  | 10     |
|                       | ×       | height (total)           |        |
| (1.5 mA in the        | 10^-10^ |                          | \[mm\] |
| Storage Ring)         |         |                          |        |
|                       | \[C\]   |                          |        |
+-----------------------+---------+--------------------------+--------+
| Mirror angle          | \~ 41   | Distance mirror          | 10     |
|                       |         | edge-beam axis (B)       |        |
|                       | \[deg\] |                          | \[mm\] |
+-----------------------+---------+--------------------------+--------+

![](media/image75.jpeg){width="3.6173611111111112in"
height="1.9513888888888888in"}

[]{#__RefHeading___Toc91568084 .anchor}Figure 3.9‑64: Synchrotron
radiation monitor at BTS bend B3, a 3D CAD view.

Alternatively, the Source Point 1 could be moved and placed at the end
of dipole B2, with a geometry of the monitor similar to the one
downstream B3. The advantages are: a larger dispersion and a larger
dispersion to horizontal beta function ratio, see Figure 3.9-61. The
disadvantages are a larger distance from the Booster (less effective
diagnostics of the booster extraction status), a tighter space
downstream B3 and additional engineering and construction effort with
increased costs.

For all the cases, the photon flux is high enough to allow the use of
standard CCD cameras with a sensitivity of \~ 1 lux.

The synchrotron radiation heat load in both the metallic mirrors is
negligible and no water-cooling is required for that. In the case of the
monitor at B3, a wrong orbit could bring the electron beam on the
mirror, the induced heat load will be approximately \~ 0.1 J per beam
passage. This number has been estimated for an aluminum 5 mm thick
mirror and for the nominal bunch charge indicated in Table 3.9-24.
Assuming an operation at currents ten times larger and 1 Hz repetition
rate, the mirror needs to be designed in order to dissipate an average
power of \~ 1 W.

#### Beam Stopper for Injection Tune-up

We are proposing the insertion of an extractable beam stopper at the end
of the BTS transferline, just before the first injection septum of the
storage ring. Such a beam stopper, when inserted, will allow for the
complete tuning of the accelerator injection chain without perturbing
the beam stored in the storage ring.

The beam stopper should have a thickness of \~ 10 radiation lengths in
order to efficiently stop the beam particles. The structure can be very
compact if high atomic number and high density materials are used. For
example, if tungsten is used the required thickness will be \~ 4 cm. The
maximum heat load will be smaller than 10 W (1 Hz and 5 nC charge). Long
term activation of the beam stopper needs to be estimated.

![](media/image76.jpeg){width="3.66875in" height="4.4625in"}

[]{#__RefHeading___Toc91568085 .anchor}Figure 3.9‑65: CAD drawing of the
BTS diagnostic beam stop. A tungsten block being inserted vertically
into the beam path.

### Storage Ring Diagnostics

####  Storage Ring Bunch Purity Monitor

During the two bunches mode of operation, bunch purity in the storage
ring must be measured. At present during two-bunch operation, we set up
a simple BPM-digital scope system with a resolution (ratio between the
charge in the main bunch and the one in the parasite bunch) of a few
units in the 10^-3^ range.

For the top-off upgrade, we propose a dedicated bunch purity monitor
with a higher resolution (\<10^-4^) that will permit an easier and more
reliable control of the bunch cleaning procedure. The proposed system is
based in a photon counting scheme using the synchrotron radiation
emitted by the bunches. The block diagram of the system is shown in
Figure 3.9-66.

![](media/image77.jpeg){width="5.083333333333333in" height="1.45in"}

[]{#__RefHeading___Toc91568086 .anchor}Figure 3.9‑66: Bunch Purity
Monitor Block Diagram.

The attenuator is required to go in the so-called single photon count
regime, where a single photon is detected every few hundred passages of
the bunch. This is fundamental for avoiding photons pile-up and for
ensuring a linear response of the system. The detector must be fast
enough to discriminate between contiguous bucket (2 ns) at a resolution
smaller than 10^-4^. This requirement is kind at the limit with what can
be achieved using synchrotron radiation in the visible range (PMT, MCP,
...) while it is well in the range of performance for x-ray detectors
like avalanche photo diodes. The signal coming from the detector is
properly formed by a discriminator and is compared in time with an orbit
clock by a time to amplitude converter. The output signal of the
converter will have an amplitude proportional to the time difference
between the orbit clock and the arrival of the detector signal. Finally,
an amplitude analyzer will present the results in the shape of amplitude
histograms.

The visible option is simpler because it can use the synchrotron
radiation already available in some of ALS beam lines (BL3.1 or BL7.2),
while for the x-ray case a new port with a thin beryllium window must be
placed somewhere for taking out the x-ray from the vacuum chamber.

####  Storage Ring Bunch-by-Bunch Current Monitor

There are several operational aspects that require an accurate
measurement of the beam current in all individual bunches in the ALS
storage ring. One is the desire of users for specific fill patterns
tailored to their needs. Others are accelerator physics issues like
lifetime and instabilities related to bunch current or details of the
fill pattern. This issue is more critical in top-off, where just random
injection timing could lead to a slow but continuous deterioration of
the fill pattern. The ALS already has a bunch-by-bunch current monitor,
however, the current system is not dedicated for this purpose, uses a
signal with poor signal quality and is not user friendly.

[]{#__RefHeading___Toc91568087 .anchor}Figure 3.9‑67: Schematic of a
bunch-by-bunch current monitor for the ALS Storage Ring.

Therefore, an upgrade of the existing system will be implemented: The
signal quality of the Beam Position Monitor signal will be improved. A
dedicated scope with higher bandwidth will be used. The signal
processing software will be included as a reliable application at a
lower level in the control system and a new high-level operator
interface will be implemented.

##  Computer Control System

The computer control system (CS) for the ALS consists of distributed
controllers installed in the proximity of the accelerator hardware which
are linked by networks to the ALS control room (CR). In the CR, standard
workstations, both Windows and UNIX/Linux based, provide the higher
level control of the facility. These workstations, known as *console
computers*, are configured with specialized applications developed
in-house to meet the needs of accelerator operations for controlling and
monitoring all the ALS subsystems. The subsystems include magnet power
supplies, electron beam diagnostics, RF, vacuum valves and ion gauges,
and insertion devices. The control requirements for these subsystems
differ somewhat between the electron gun, LINAC, booster, storage ring
and transfer lines, but since maintenance costs increase in proportion
to the to these differences, the goal in specifying CS hardware and
software is to maintain as much commonality as possible between similar
subsystems.

The original design of the CS described in the 1-2 Gev Synchrotron
Radiation Source Conceptual Design Report (LBL PUB-5172), has greatly
evolved over the almost 20 years since the design was completed. The CS
is now in the midst of a migration from controls based on in-house
developed local controllers, Intelligent Local Controllers (ILCs) linked
by RS-485-based serial networks, to commercial bus-based (VME and cPCI)
controllers, Input Output Controllers (IOCs), linked by standard
Ethernet networks. This hardware migration enables a migration of the CS
software to the EPICS system currently in use at most other light
sources such as the Advanced Photon Source at Argonne National Lab and
the Swiss Light Source.

The detailed CS plan for the Booster Top-off effort is driven both by
the requirements of the changing hardware, such as new magnet power
supplies and the RF subsystem and the by goals for the CS at large;
namely the goal to minimize the differences in control interfaces
between similar subsystems and the goal to continue the migration of the
CS hardware and software to off-the-shelf solutions in the interest of
maintainability over the long life span of the booster.

The control requirements for each of the subsystems affected by the
booster upgrade will be discussed followed by a discussion of the
software effort. Finally, an inventory of the new control system i/o
crates and their functions are discussed.

### Magnet Power Supplies

The booster magnet power supplies have the property that their currents
must change together to maintain the electron orbit as the energy of the
booster is changed. The booster supplies are divided into *large*
supplies: the main bend (1) and the quadrupoles (4) and the *small*
supplies: the sextupoles (8) and the correctors (32).

The current scheme for ramping these magnets is based on following the
field of the main bend magnet using a gauss clock to generate an
interrupt to the controllers about every 100ms as the field increases.
Due to inflexibility of this scheme and the wide availability and low
cost of digital controls, a new system is envisioned that will drive the
ramp profile with programmable waveform generators. We expect to follow
the industry trend in control of the large supplies by specifying
integrated vendor-supplied PLC based controls with a digital interface
to the CS and an internal waveform generator for ramping the current.
Integrating the controls in the power supply reduces the wire count and
simplifies the software effort significantly. Software effort can be
reduced further by specifying a well supported wire-protocol such as
MODBUS/TCP which is supported by many PLC vendors. This protocol is
already in use in the CS and can be efficiently extended to power supply
controls.

The large number (40) of small supplies and their individual cost do not
warrant the expense of digital interfaces. These supplies would be
controlled in the traditional analog fashion by the addition of some 5
additional IOCs identical to the ones already in use in the storage
ring. Ramping of these supplies would require an external timing signal
supplied to each IOC.

The *fast* magnet power supply category includes the thin and thick
septum magnets and the kicker magnets in the booster and the thick and
thin septum magnet and the bump magnets in the storage ring. There is no
change expected in the control requirements for these magnets.

The BTS bend magnets are large supplies for which the digital controls
identical to the large supplies in the booster (minus the waveform
generator) would be used.

### BTS Diagnostics

There will be two **synchrotron light monitors** at two bending magnets
in the BTS, each with a CCD camera. In addition, a linear actuator will
allow the positioning of a mirror inside the vacuum chamber for
reflecting synchrotron light. Control of these cameras and the linear
actuator will be done by a dedicated PC, similar to the system already
deployed in the 7.1 beamline.

An insertable **beam stop** at the very end of the BTS will allow
operating the injector for tune-up without injecting in the storage
ring. The actuator position, either in or out of the beam, will be
remotely controlled from the control room.

The existing current monitors, both the **Integrated Current
Transformers** (ICT) in the BTS and the **wall current monitors** (WC)
in the booster, will require ADCs (6) for measurement of peak or average
current. These measured values should be displayed in the control room
by a new application.

### Booster Diagnostics

A **bunch cleaning** system will be installed in the booster. It uses an
arbitrary function generator and a RF synthesizer. They will be placed
somewhere inside the ALS dome and should be remotely controlled.

A single-blade **beam scraper** will be added to the booster.
Micrometric control of the scraper position is required.

### Booster RF

The controls for the RF will also be integrated into the hardware and a
digital interface, ideally with the same MODBUS/TCP wire-protocol used
for the large magnet supplies, provided to the CS.

### Radiation Protection

The CS never takes an active role in Radiation Protection or any form of
personnel safety. There will be modifications to the existing CR alarm
monitoring application that will be required in response to the expected
hardware changes however.

### Collimation Controls

There will be motor-controlled collimators added to both the BTS and
storage ring. Control of these motors will require the addition of 2
IOCs with motor control boards identical to those used for the current
scrapper controls in the storage ring.

### Software Effort

Software Effort falls into 2 main categories: IOC software development
and Control Room (CR) application development.

### IOC software effort

The software effort can be greatly reduced by reducing the different
types of interfaces to accelerator equipment. The standard digital
interface should be Ethernet based and should support MODBUS/TCP for
communications with the IOCs.

There will be IOC development effort for controlling the new digital
supplies (both ramped and non-ramped). This effort will start with the
development of interface specifications for the type of PLC and the
communication mechanism (serial or Ethernet) and the communication
protocol. Then an IOC template for the PS must be developed that handles
PS process variables. For testing this template it will be essential to
procure some version of the digital control hardware from the vendor
early.

There will also be an IOC software development effort required for the
analog controlled ramped supplies. Interrupt driven software must be
written to respond to the incoming 'ramp step' interrupt generated by
the timing system as the booster is ramped to full energy.

Two IOCs will be used to control the new booster RF system. The
transmitter is a commercial unit with internal digital controls (similar
to the large PSs) with a serial or, preferably, an Ethernet interface
using the MODBUS protocol (again similar to the large PSs). A PLC based
RF Interface Chassis will also be controlled by an IOC.

### Control Room Application Development

Many of the changes and additions made to the booster instrumentation
also require changes and additions to CR applications. Development of CR
typically includes testing during dedicated machine time for both
development and application commissioning. Application commissioning
typically involves a team consisting of a controls group member, the
instrumentation lead engineer or accelerator physicist and an
accelerator operator. Although they have not been established, the need
for the following applications has been identified:

-   Booster RF Controls.

-   Booster Tune-up. Insert/Remove BTS beam stop. Display current
    monitors.

-   Booster Bunch Cleaning. Control waveform generator.

-   Booster Scraper control.

-   Booster BPM.

-   BTS Synchrotron Light Monitor.

-   Storage Ring collimator controls

-   Radiation monitoring.

### New IOCs

About 10 new IOCs will be required for the top-off project. The number
is dictated mainly by the I/O capacity but also by the requirement that
they be located within the proximity of the hardware that they must
control. It is also quite important, given the large number of IOCs that
need to managed, that, where possible, these additional crates use
hardware and software that is currently used elsewhere in the
accelerator.

IOC1 booster (40 PVs)

-   Digital magnet supplies (7)

IOC2-5 booster (20 ILC replacements, 300 PVs)

-   Booster corrector supplies

-   Thick and Thin Septum magnet supplies

-   Kicker supply

-   Magnet thermocouples (20 PVs/ea)

IOC6 booster (12 PVs)

-   Booster scraper

IOC7 booster diagnostics (20 PVs)

-   Bunch cleaning waveform generator and amp

-   Current transformer ADC (5) (maybe LTB)

-   Wall current monitor readout ADC (1)

IOC8 booster RF (100 PVs)

-   transmitter

```{=html}
<!-- -->
```
-   interface chassis

IOC9 VME BTS (12 PVs)

-   collimator

IOC10 BTS diagnostics

-   beam stop????

IOC11-12 VME storage ring (12 PVs)

-   2 collimators

-   Radiation monitors???

##  AC Power Utilities

### AC Power Utilities-Booster Ring

### Description-General

The Advanced Light Source Booster Ring AC Power (Bank 303) is derived
from a 2MVA, 12.47KV-480Y/277V transformer which feeds a 3200Amp, 480V,
3 phase distribution panel (SS303) located at the ALS Switching Station
A3. Reference 4B06E179B for basic one-line diagram.

SS303 currently houses 3 each distribution circuit breakers.

Circuit 1 supplies 480VAC, 400Amp power to Panel 303A1A located within
the Booster Pit Area Sector 3 via 1 each 3/C-500MCM cable. Panel 303A1A
is the distribution panel used to power the Booster QF and QD Power
Supplies. The current load on this panel is approximately ½ of its
designed rating. No AC Power Utility upgrade will be required for the
new QF and QD Power Supplies which will be required for the Booster
Upgrade Project.

Circuit 2 supplies 480VAC, 800 Amp power to the Booster Dipole Power
Supply located within the Booster Pit Area Sector 1 via 2 sets of
3/C-500MCM cables. Each set of 3/C-500MCM cables are located within a 4"
Conduit. The new Booster Dipole Power Supply will be designed such as
the input ac power requirements will not exceed the factory operating
characteristic curve of the existing 800Amp feed breaker and input ac
power cabling. No AC Power Utility upgrade will be required for the new
Booster Dipole Power Supply.

Circuit 3 supplies 480VAC, 400 Amp power to Panel 303A3A located within
the Booster Pit Area Sector 3 via 1 each 3/C-500MCM cable. Panel 303A3A
is the distribution panel used to distribute 208-120Vac power to each of
the Booster Quadrants via 3 each 75KVA (Sectors 1,2,4) and 1 each
112.5KVA (Sector 3) 480V-208V step down transformers located in the
Booster Pit Area Sector 3. This power distribution is for all booster
ring system support loads requiring lower voltages. No AC Power Utility
upgrade will be required in this area for the Booster Upgrade Project.

### Booster RF AC Power

The Advanced Light Source Booster RF AC Power is derived from a 2MVA,
12.47KV-480Y/277V transformer which feeds a 3200Amp, 480V, 3 phase
distribution panel (SS302) located at the ALS Switching Station A3.

Reference 4B06E178C for basic one-line diagram.

SS302 circuit 1 supplies 480VAC, 1200Amp power to Panel 302A1A located
near the ALS Linac entrance. Panel 302A1A is fed via 3 sets of
3/C-500MCM cables and has a current limit of 1200amps. Circuit 5, 80Amp
feed supplies input power to the existing Booster Ring RF Transmitter
Power Supply and circuit 6, 60amp feed supplies power to the existing BR
RF Cavity Water System. The existing circuit 6 will be removed and a
local utility upgrade will be needed for the new ALS Booster RF
Transmitter. Panel 302A1A has multiple spare circuits and circuit
breakers. No AC Power Utility upgrade will be required for panel 302A1A
for the Booster Upgrade Project.

### Booster to Storage Ring (BTS)

AC Power for the 4 each BTS Bend Magnet Power Supplies is fed from the
Storage Ring/Linac Distribution Power SS 302 circuit 1 via distribution
panel 302A1A located near the Linac entrance area. Panel 302A1A circuits
7-10 supply the 480V input power feeds for each of the BTS Bend Magnet
Power Supplies. Reference 4B06E178A for basic one-line diagram. No AC
Power Utility upgrade will be required for the new BTS Bend Magnet Power
Supplies required for the Booster Upgrade Project.

![](media/image78.jpeg){width="6.892361111111111in"
height="8.623611111111112in"}

[]{#__RefHeading___Toc91568088 .anchor}Figure 3.11‑68: Diagram of the
electrical supply bank 303 at the ALS.

![](media/image79.jpeg){width="6.367361111111111in"
height="7.959722222222222in"}

[]{#__RefHeading___Toc91568089 .anchor}Figure 3.11‑69: Diagram of the AC
supply bank 302 at the ALS.

# Cost, Schedule, Installation

## Project Organization

The Top-off upgrade of the ALS has been treated ALS internally like a
project since the project kick-off meeting in October 2003. All
applicable project management tools are used. The organization chart of
the project is shown below. Everybody listed on the organization chart
has full line responsibilities, i.e. safety, technical, cost, and
schedule responsibility. The ALS division directorate provides
management oversight and all project decisions are closely coordinated
with ALS management.

Identifying risks, analyzing and resolving them was the main emphasis of
the conceptual design phase in FY04. The project management identified
an initial list of major risk items. Later input was solicited from all
project team members. Based on this list, a prioritized list of studies
for the conceptual design phase was assembled and all high risk items
were studied intensively. At the time of this CDR, most high risk items
have been successfully resolved. The few remaining items are currently
actively being studied, with positive results so far. After finishing
the CDR, the risk analysis will be formalized further and detailed
mitigation plans will be documented for all remaining risk items.

With the completion of the CDR, the scope of the top-off upgrade will be
frozen and a formal change control process will be put in place. All
future changes to the scope, parameter list/configuration, or requests
to use cost or schedule contingency will have to be approved by the
project management. Significant changes will also need approval by ALS
management.

## Work Breakdown Structure

The Work Breakdown Structure (WBS) was created shortly after the project
kick-off in October 2003. It has slightly evolved over time, and so far
changes were just informally approved by project management (and
discussed with ALS management).

Once this CDR is finished, the WBS will be frozen. Afterwards changes
will be approved only with a formal change control process. The WBS also
includes the conceptual design phase. Therefore there are some WBS items
with zero cost in the cost estimate, since all effort in those was in
last fiscal year and does not show up in cost-to-complete.

1.1 Project Management

1.2 Top Off Documentation

1.2.1 User Requirements

1.2.2 Specification

1.2.3 CDR

1.3 Linac

1.3.1 EDI

1.3.2 Beam Loading Compensation

1.3.3 Diagnostics

1.4 Booster

1.4.1 Power Supplies

1.4.2 Thin Septum Magnet

1.4.3 Thick Septum Magnet

1.4.4 Kicker Magnet

1.4.5 RF

1.4.6 Diagnostics

1.4.7 Bump Magnets

1.5 BTS

1.5.1 EDI

1.5.2 Diagnostics

1.5.3 Beam Stopper for Injection Tune-Up

1.5.4 B1-B4 bend power supplies

1.6 Storage Ring

1.6.1 Bump Magnets

1.6.2 Thin Septum Magnet

1.6.3 Thick Septum Magnet

1.6.4 Radiation Protection

1.6.6 Diagnostics

1.7 Controls and Timing

1.7.1 User Gating Signal

1.7.2 Linac and Booster Timing

1.7.3 Controls

1.7.4 RF Controls

1.8 Commissioning

1.8.1 Pre-commissioning

1.8.2 Commissioning/Startup

## Cost Estimate

The cost estimate shows cost to complete from December 2004 on. It
includes the full scope of the top-off upgrade as presented in Section
2.2. It includes all necessary spare parts and is based on FY05 craft
rates, with full burden. Escalation is not included in the cost
estimate. Based on the current schedule of the project, i.e. completion
in spring of 2006, escalation costs are relatively small (i.e. about 75
k\$) and will be covered out of contingency.

All effort, including staff people on operations funding is included
(e.g. commissioning time). Routine accelerator physics studies part of
the precommissioning are not included and instead are funded out of the
operations budget. Safety is an integral part of the project. The cost
of complying with all applicable OSHA regulations and the electrical
code is not shown separately but included everywhere in the cost
estimate. EH+S support staff is heavily involved at all stages of the
project. Their salaries are paid out of ALS operations funds and are not
included in the cost estimate.

Contingency is applied at level 3 of the WBS and the overall contingency
is 21%. The complete cost estimate is included as an appendix and can be
found in Section 7.2.

![](media/image80.wmf)

[]{#__RefHeading___Toc91568115 .anchor}Table 4.3‑25: Summary of the cost
estimate for the ALS Top-off upgrade as of November 19, 2004.

![](media/image81.wmf)

[]{#__RefHeading___Toc91568116 .anchor}Table 4.3‑26: Cost estimate down
to WBS level 3 for the ALS top-off upgrade as of November 19, 2004.

## Draft Schedule

This CDR tries to evaluate the optimum schedule imaginable without
funding profile limitations, so that we would be ready independent of
what the final profile will be. The optimum schedule

assumes availability of significant additional funding in FY05 (starting
sometimes around March). This would provide the possibility to purchase
long lead items early enough and consequently the project could be
completed in FY06. For the schedule and cost estimate presented here, we
would need a total of about 2.4 M\$ in FY05, and the rest in FY06. There
is uncertainty on a funding profile from DOE at this time. So far 500
k\$ are available for the Top-off upgrade for FY05 (given in FY04).

![](media/image82.png){width="5.894444444444445in"
height="4.440277777777778in"}

![](media/image83.png){width="5.8902777777777775in"
height="4.4319444444444445in"}

![](media/image84.png){width="5.8875in" height="4.428472222222222in"}

![](media/image85.png){width="5.883333333333334in"
height="4.428472222222222in"}

![](media/image86.png){width="5.8875in" height="4.432638888888889in"}

![](media/image87.png){width="5.90625in" height="4.432638888888889in"}

![](media/image88.png){width="5.8902777777777775in"
height="4.438888888888889in"}

![](media/image89.png){width="5.894444444444445in"
height="4.4319444444444445in"}

![](media/image90.png){width="5.883333333333334in"
height="4.427777777777778in"}

[]{#__RefHeading___Toc91568090 .anchor}Figure 4.4‑70: Complete draft
schedule for the ALS Top-off upgrade as of November 19, 2004.

Depending on when and how much money becomes available, a staged
approach might be necessary. The possible stages of the project could
be:

1.  Immediate need is to conclude radiation safety studies so that DOE
    approval process for Final Safety Analysis Document (FSAD) change
    can be started.

    -   First priority: Install scrapers and collimators

2.  Next one could purchase long lead items for booster energy upgrade
    (RF windows, power supplies, RF transmitter, ...).

3.  Then one would complete everything necessary for full energy
    injection.

4.  Next one could install the radiation protection equipment necessary
    for injection with shutters open (true top-off).

5.  Last one would install equipment necessary for bunch cleaning in
    booster and the corresponding diagnostics equipment.

## Installation

The schedule presented above includes basic installation details for all
subcomponents. However, we will develop a separate installation schedule
with higher level of detail at a later time. The installation schedule
will consolidate the top-off upgrade with all other non top-off upgrade
tasks also performed during the same shutdown. Nevertheless, the level
of detail present in the schedule right now is sufficient to conclude
that the installation of all components in one, about 6 week long,
shutdown is possible.

The relatively short installation shutdown is facilitated by the fact
that very little mechanical work is necessary, very few high power
cables need to be rerouted, and several components can be installed (or
test-installed) beforehand (pulsed magnet upgrades, full RF transmitter,
etc.). All of these factors minimize the workload in the actual
shutdown. Furthermore, nearly all smaller equipment (amplifiers,
diagnostics, collimators, scrapers, etc.) will be installed in routine
(2 day) shutdowns before big installation shutdown. The main schedule
drivers for the length of the shutdown are the installation and final
tests of the new booster RF transmitter, as well as the installation and
test of all new slow/ramped power supplies for the booster and the BTS
line.

## Commissioning

In order to ensure a smooth final transition period with low
commissioning risk and minimal teething period for the users,
precommissioning is an integral part of project plan. The main tasks
that will be investigated during the early precommissioning phase were
described in the radiation safety and accelerator physics sections.

The actual commissioning period will intrinsically include time without
beam, to test coordinated control and ramping of all new components. A
commissioning period of about 2 weeks seems very reasonable, given
sufficient pre-commissioning studies:

-   Many beam diagnostics elements are already there. Enabling a
    complete set of reference measurements to be taken.

-   Pulsed magnets will be upgraded beforehand.

-   RF transmitter will be fully tested months before.

The first 5 days of commissioning will be without beam. The next 5 days
will be dedicated to injector commissioning with beam. The final 4 days
consist mostly of routine storage ring startup. The commissioning of the
true top-off operation with beamline shutters open would be done
incrementally in normal accelerator physics shifts during the months
following the initial commissioning.

The minimum goal at the end of the commissioning is to return to the
nominal 1.5 GeV injection used up to the installation shutdown with
comparable performance. However, it is expected and a goal of the
project, to provide 1.9 GeV full energy injection without any ramping by
the end of the initial commissioning period.

The move to injection with shutters open, higher beam currents and
smaller beamsizes on the other hand is planned to be implemented
gradually and in close cooperation with all users over the months
following the initial commissioning period. It is expected that the full
implementation will probably take several months. Operation at the
nominal upgrade parameters is expected to be possible about 6 months
after the initial commissioning.

# Acknowledgments

The editors wish to acknowledge the many members of the ALS staff who
contributed to the formulation of these upgrade plans, particularly the
members of the top-off project team who wrote large sections of this
design report. We are very grateful to the ALS management for its strong
support of the upgrade plans and the close cooperation in implementing
them. Finally we are very grateful to the colleagues who reviewed the
top-off project in November 2004 and who helped to fine tune our upgrade
plans.

This work was supported by the Director, Office of Science, Office of
Basic Energy Sciences, of the U.S. Department of Energy under Contract
No. DE-AC03-76SF00098.

# References

\[1\] A. Lanzara, et al., "Evidence for ubiquitous strong
electron--phonon coupling in high-temperature superconductors," *Nature*
412, 510 (2001).

\[2\] A.D. Gromko et al, "Mass-renormalized electronic excitations at
(π, 0) in the superconducting state of Bi~2~Sr~2~CaCu~2~O~8+x~"
*Physical Review B* 68, 174520 (2003).

\[3\] *Workshop on "Soft X-Ray Science in the Next Millenium: The Future
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18, 2000), prepared by Oak Ridge National Laboratory for the U.S.
Department of Energy.

\[4\] A. Scholl et al., "Observation of antiferromagnetic domains in
epitaxial thin films," *Science* 287, 1014 (2000).

\[5\] J. Stohr et al., "Images of the antiferromagnetic structure of a
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\[6\] F. Nolting et al., "Direct observation of the alignment of
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\[7\] H. Ohldag et al.. "Spectroscopic identification and direct imaging
of interfacial magnetic spins," *Phys. Rev. Lett.* 87, 247201 (2001).

\[8\] H. Ohldag et al., "Spin reorientation at the antiferromagnetic
NiO(001) surface in response to an adjacent ferromagnet," *Phys. Rev.
Lett.* 86, 2878 (2001), and references therein to ALS magnetic
microscopy.

\[9\] J. Feng et al., "An Aberration Corrected Photoemission Electron
Microscope at the Advanced Light Source," AIP Conf. Proc. 705, 1070
(2004).

\[10\] S.A. Wolf et al., "Spintronics: A spin-based electronics vision
for the future ," *Science* 294, 1488 (2001).

\[11\] R. Schoenlein, "Femtosecond x-rays from relativistic electrons:
New tools for probing structural dynamics," *Comptes Rendus de l
Academie des Sciences Serie IV Physique Astrophysique* 2, 1373 (2001);
P. A. Heimann, H. A. Padmore, and R. W. Schoenlein, "ALS Beamline 6.0
For Ultrafast X-ray Absorption Spectroscopy," *AIP Conf. Proc.* 705 (1),
1407 (2004).

\[12\] J. Miao, "High-resolution 3D x-ray diffraction microscopy,"
*Phys. Rev. Lett.* 89, 088303 (2002).

\[13\] S. Marchesini et al., "X-ray image reconstruction from a
diffraction pattern alone," *Phys. Rev. B* 68, 140101(R) (2003).

\[14\] J. Chavanne, P. Elleaume, and P. Van Vaerenbergh, "Recent
developments of insertion devices at the ESRF," in *Proceedings of the
1999 Particle Accelerator Conference*, New York, 1999.

\[15\] T. Hara, T. Tanaka, T. Tanabe, X.M. Marechal, S. Okada, and H.
Kitamura, "In-vacuum undulators of SPring-8," *J. Synchrotron Rad.* 5,
403 (1998).

\[16\] R. Schlueter, S. Marks, S. Prestemon, and D. Dietderich,
"Superconducting undulator research at LBNL," *Synchrotron Radiation
News* 17(1), 33 (2004).

\[17\] S. Prestemon, D. Dietderich, S. Marks, and R. Schlueter, "NbTi
and Nb~3~Sn Superconducting Undulator Designs," *AIP Conf. Proc.* 705,
294 (2004).

\[18\] C. Steier, D. Robin, A. Wolski, G. Portmann, and J. Safranek,
\"Coupling Correction and Beam Dynamics at Ultralow Vertical Emittance
in the ALS,\" in *Proceedings of the 2003 Particle Accelerator
Conference*, 3213-3215.

\[19\] L. Emery and M. Borland, Proceedings of the 1999 Particle
Accelerator Conference (1999) 200-202

\[20\] M Boege, Proceedings of the 2002 European Particle Accelerator
Conference (2002) 39-43

\[21\] H. Tanaka et al, Proceedings of the 2004 European Particle
Accelerator Conference

\[22\] H. Nishimura, "The Horizontal Orbit When SR08C SuperBend is
Tripping", LSAP Note \# (2004)

\[23\] M. Borland and L. Emery, Proceedings of the 1999 Particle
Accelerator Conference, New York 2319 -- 2321 (1999)

\[24\] L. Favraque, Private Communication

\[25\] Engineerng Note: Light Source -- Booster Extraction Bump Magnets.
AL0323, M6852

\[26\] G.Stover "Comparison of Booster ring \"Bump magnet\" B field
measurements vs. calculations @ 1.522 and 2.0 Gev." ALS Top-Off Project
Note 04/19/2004

\[27\] S.Kwiatkowski "Do we need to modify the Booster fast extraction
kicker for Top-Off operation?" ALS Top-Off Project Note 02/20/2002

\[28\] "High Energy Linacs": Applications to Storage Ring RF Systems and
Linear Colliders, Perry B. Wilson SLAC Publication 1991

\[29\] M.Sands. "Observation of Quantum Effects in an Electron
Synchrotron." International Conference on Accelerators, CERN, 1959

\[30\] M.Sands. "Physics of Electron Storage Rings." SLAC Report No. 121
(1970).

\[31\] N. Sereno, Proceedings of the 1999 Particle Accelerator
Conference, New York, US, 1999, p. 2322.

\[32\] H. Suzuki, *et al*., Nuclear Instruments and Methods in Physics
Research A 444 (2000) 515-533.

\[33\] T. Aoki, *et al*., Proceedings of the 2003 Particle Accelerator
Conference, Portland, US, May 2003, p. 2551.

\[34\] E. Plouviez, ESRF Machine Technical Note 01-04/MDT.

\[35\] E. Plouviez, P. Ellaume, private communications.

## List of Figures

[Figure 1.2‑1: Parameters of top-off injection after the upgrade with
reduced vertical emittance. 9](#__RefHeading___Toc91568021)

[Figure 1.2‑2: Brightness comparison of new ALS insertion devices to
current insertion devices. 10](#__RefHeading___Toc91568022)

[Figure 1.3‑1: Beamlines at the ALS. In the upgrade, the five
"workhorse" 4.45-m-long U5, U8, and U10 undulators would be replaced
with nine shorter, small-gap devices with higher brightness in an
orderly, phased manner to minimize disruption of the experimental
program. 11](#__RefHeading___Toc91568023)

[Figure 2.1‑1: Layout of our present injection system
14](#__RefHeading___Toc91568024)

[Figure 2.1‑2: Booster ramping cycle. 15](#__RefHeading___Toc91568025)

[Figure 3.1‑1: Heating induced focusing error on sagittally focusing
mirror. 20](#__RefHeading___Toc91568026)

[Figure 3.1‑2: Fast (vertical and horizontal) oscillation of the beam,
due to mismatch of the bump magnets. This lasts less than 1 ms.
22](#__RefHeading___Toc91568027)

[Figure 3.1‑3: Slower (horizontal) closed orbit distortion, due to the
septum magnet eddy currents, that lasts about 0.1 s.
23](#__RefHeading___Toc91568028)

[Figure 3.1‑4: Injection transients causing an intensity fluctuation
during a horizontal line scan in STXM at beam line 11.0.2 (second test 7
Dec 2003). Septum magnet turned off. One horizontal line scan takes 60
ms. 24](#__RefHeading___Toc91568029)

[Figure 3.2‑1: Locations of Radiation Monitors at the ALS.
26](#__RefHeading___Toc91568030)

[Figure 3.2‑2: Active Radiation Monitors: Interlocked Neutron/Gamma
Monitors (left) and Optics Gamma Monitors (right).
27](#__RefHeading___Toc91568031)

[Figure 3.2‑3: Passive Radiation Monitors: In-close dosimeters (left)
and Peripheral dosimeters (right). 27](#__RefHeading___Toc91568032)

[Figure 3.2‑4: Passive Dose equivalent at 30 cm of one injected pulse of
electrons carrying 1 nC of charge striking a high Z material.
30](#__RefHeading___Toc91568033)

[Figure 3.2‑5: Geometry of x.1 beamline. Rays A-D mark the extremes in
angle and offset that still pass through the frontend apertures. Ray N
marks the nominal center of a x.1 beamline.
31](#__RefHeading___Toc91568034)

[Figure 3.2‑6: Maximum distance injected back to SR injection point.
32](#__RefHeading___Toc91568035)

[Figure 3.2‑7: Trajectories of several important particles
33](#__RefHeading___Toc91568036)

[Figure 3.2‑8: Jackson hole locations on arc sector
34](#__RefHeading___Toc91568037)

[Figure 3.2‑9: Closed orbit distortion following rf trip.
35](#__RefHeading___Toc91568038)

[Figure 3.2‑10: Beam loss at SR02 JH6 and SR03 JH1 as a function of JH
half gap height. 36](#__RefHeading___Toc91568039)

[Figure 3.2‑11: CAD drawing of the double sided horizontal collimator
for the BTS transfer line. 37](#__RefHeading___Toc91568040)

[Figure 3.2‑12: A pair of vertical scrapers installed in the so-called
Jackson holes of one of the storage ring arc vacuum chambers.
38](#__RefHeading___Toc91568041)

[Figure 3.2‑13: Drive system, cooling and inner structure of vertical
scrapers. 39](#__RefHeading___Toc91568042)

[Figure 3.2‑14: Potential operational modes and logic for transitioning
between them both for the current ALS operation and for top-off. B1 and
B2 are the first two bending magnets in the booster to storage ring
(BTS) transfer line. 41](#__RefHeading___Toc91568043)

[Figure 3.2‑15: Logic of a (potential) beam line radiation monitor
interlock system. 43](#__RefHeading___Toc91568044)

[Figure 3.3‑1: Histograms showing the results of simulated vertical
emittance and dispersion correction for 100 randomly misaligned error
seeds. 46](#__RefHeading___Toc91568045)

[Figure 3.3‑2: Horizontal/vertical beamsize and beam tilt as calculated
from calibrated machine model using orbit response matrix analysis. The
blue case is before coupling correction, the green one after one
iteration. 47](#__RefHeading___Toc91568046)

[Figure 3.3‑3: Vertical beamsize for two four day periods. Using a
global vertical dispersion wave to increase the vertical emittance
(right) leads to a much better beamsize stability than excitation of the
coupling resonance (left). 48](#__RefHeading___Toc91568047)

[Figure 3.3‑4: Measured lifetime of the ALS versus half aperture in one
straight for three different cases: excited coupling resonance (red),
corrected coupling and vertical dispersion (green), vertical dispersion
wave (blue). The two cases with excited coupling resonance and
dispersion wave were measured for identical vertical emittance.
49](#__RefHeading___Toc91568048)

[Figure 3.3‑5: Lifetime of the ALS versus half aperture in one straight,
measured using a scraper: The lifetime reduction for a lattice with
corrected coupling and vertical dispersion wave to increase the vertical
emittance is small down to a full vertical aperture of about 5 mm.
50](#__RefHeading___Toc91568049)

[Figure 3.3‑6: Dependence of ALS injection efficiency (without
re-optimization) on insertion device settings. Only the W11 wiggler
reduces the injection efficiency significantly. Because the integration
time of the storage ring current monitor is not exactly matched to the
injector period, the measurements have some jitter around the correct
values. This also explains why some of the measurements indicate
injection efficiencies above 100%. 51](#__RefHeading___Toc91568050)

[Figure 3.3‑7: Dependence of ALS injection efficiency on the vertical
physical aperture in the storage ring without any re-optimization. The
aperture was changed by opening and closing two vertical scrapers in
straight 3 at a beta function of about 6 m.
52](#__RefHeading___Toc91568051)

[Figure 3.3‑8: Reduction in radiation dose at first optics in beamline
4.0 due to ALS beam dump using a vertical collimator at the end of
straight 3. The vertical axis shows average count rates of radiation
monitors and the horizontal axis is time in minutes. Shown are 3
(intentional) beam dumps with equal stored beam current. After the first
dump with scraper open, the scraper (at a vertical beta function of
about 6 m) was set to a full aperture of 8 mm for the second, and 5 mm
for the third beam dump. 53](#__RefHeading___Toc91568052)

[Figure 3.5‑1: Booster extraction magnets.
60](#__RefHeading___Toc91568053)

[Figure 3.5‑2: Storage Ring injection area.
61](#__RefHeading___Toc91568054)

[Figure 3.5‑3: Timing diagram for booster/storage extraction/injection
magnets. Time periods not to scale 62](#__RefHeading___Toc91568055)

[Figure 3.5‑4: Location of booster extraction magnets.
63](#__RefHeading___Toc91568056)

[Figure 3.5‑5: Bump Magnets core and coil geometry
64](#__RefHeading___Toc91568057)

[Figure 3.5‑6: Basic discharge circuit 64](#__RefHeading___Toc91568058)

[Figure 3.5‑7: Waveform pictures taken at peak drive current of 312 amps
66](#__RefHeading___Toc91568059)

[Figure 3.5‑8: Field versus current transfer function for the second
booster extraction bump magnet. 66](#__RefHeading___Toc91568060)

[Figure 3.5‑9: INSOFT Half magnet simulation of B field @ 2.0 Gev
69](#__RefHeading___Toc91568061)

[Figure 3.5‑10: Drawing of kicker test stand arrangement.
70](#__RefHeading___Toc91568062)

[Figure 3.5‑11: Basic discharge circuit for the thin and thick septum
magnet 72](#__RefHeading___Toc91568063)

[Figure 3.5‑12: Basic discharge circuit waveforms for the thick septum
magnet 73](#__RefHeading___Toc91568064)

[Figure 3.5‑13: Top view of Septa magnet layout -- SR straight. Each
magnet sectioned through the horizontal midplane.
75](#__RefHeading___Toc91568065)

[Figure 3.5‑14: Thick (left) and thin (right) Septa cross sections --
(needs to be resized) 75](#__RefHeading___Toc91568066)

[Figure 3.5‑15: Vertical B field component along the transverse width of
the gap at the mid-plane. For 1.525 Gev, 2.0 Gev, and + 10%
78](#__RefHeading___Toc91568067)

[Figure 3.5‑16: Thin septum high current (B=0.40T) curve normalized to
the present nominal current (B=0.30T) across the gap midplane, near the
narrow end. 79](#__RefHeading___Toc91568068)

[Figure 3.5‑17: Beam orbit distortion due to slowly decaying eddy
currents in thick septum magnet. 80](#__RefHeading___Toc91568069)

[Figure 3.5‑18: Thick septum at peak field (1.33 tesla) of half sine
pulse 81](#__RefHeading___Toc91568070)

[Figure 3.5‑19: Thick septum at zero field at end of half sine pulse
82](#__RefHeading___Toc91568071)

[Figure 3.5‑20: Thick septum stray field at its maximum value at 1.0
msec after the start of the 'half sine' current pulse.
83](#__RefHeading___Toc91568072)

[Figure 3.5‑21: Flux lines at the end of a damped 'full sine' current
pulse using a measured damping factor of (93.5% voltage reversal)
84](#__RefHeading___Toc91568073)

[Figure 3.5‑22: Predicted time history of this stray field integral
along the beam axis and measured orbit distortion for half-sine and
damped full-sine case. 85](#__RefHeading___Toc91568074)

[Figure 3.5‑23: Rod-plane insulation tests from Alston
87](#__RefHeading___Toc91568075)

[Figure 3.5‑24: One of four bipolar switch modules
91](#__RefHeading___Toc91568076)

[Figure 3.8‑1: Principal drawing of Booster RF system.
98](#__RefHeading___Toc91568077)

[Figure 3.8‑2: RF buckets and particle distribution in ALS Booster at
1.9 GeV. 103](#__RefHeading___Toc91568078)

[Figure 3.8‑3: RF buckets and 10 injected linac bunches into ALS Booster
at 50 MeV. 103](#__RefHeading___Toc91568079)

[Figure 3.9‑1: Bunch cleaning system schematics
109](#__RefHeading___Toc91568080)

[Figure 3.9‑2: BTS optical function, beam sizes and SR source point
positions. 114](#__RefHeading___Toc91568081)

[Figure 3.9‑3: Synchrotron radiation monitor at BTS bend B1.
115](#__RefHeading___Toc91568082)

[Figure 3.9‑4: Synchrotron radiation monitor at BTS bend B3 and detail
of the mirror area. For the symbols in the figure see Table 3.9‑5.
116](#__RefHeading___Toc91568083)

[Figure 3.9‑5: Synchrotron radiation monitor at BTS bend B3, a 3D CAD
view. 116](#__RefHeading___Toc91568084)

[Figure 3.9‑6: CAD drawing of the BTS diagnostic beam stop. A tungsten
block being inserted vertically into the beam path.
118](#__RefHeading___Toc91568085)

[Figure 3.9‑7: Bunch Purity Monitor Block Diagram.
119](#__RefHeading___Toc91568086)

[Figure 3.9‑8: Schematic of a bunch-by-bunch current monitor for the ALS
Storage Ring. 119](#__RefHeading___Toc91568087)

[Figure 3.11‑1: Diagram of the electrical supply bank 303 at the ALS.
128](#__RefHeading___Toc91568088)

[Figure 3.11‑2: Diagram of the AC supply bank 302 at the ALS.
129](#__RefHeading___Toc91568089)

[Figure 4.4‑1: Complete draft schedule for the ALS Top-off upgrade as of
November 19, 2004. 139](#__RefHeading___Toc91568090)

## List of Tables

[Table 1.2‑1: Comparison of Present and Future Storage-Ring Parameters
9](#__RefHeading___Toc91568091)

[Table 1.2‑2: Comparison of Present and Future Brightness
(photons/sec/0.01%bw /mm^2^/mrad^2^) 10](#__RefHeading___Toc91568092)

[Table 2.2‑1: Difference between present operation and operation after
the top-off upgrade 18](#__RefHeading___Toc91568093)

[Table 3.1‑1: Operational parameters chosen as goal for the ALS top-off
upgrade. 20](#__RefHeading___Toc91568094)

[Table 3.2‑1: A January 2004 summary report of the in-close gamma and
neutron monitors. 28](#__RefHeading___Toc91568095)

[Table 3.2‑2: Geometry parameters of the apertures for a x.1 beamline.
31](#__RefHeading___Toc91568096)

[Table 3.4‑1: Injection System Faults/Failures 1 Oct 03 to 1 Oct 04
56](#__RefHeading___Toc91568097)

[Table 3.5‑1: Current and future operation parameters for booster
extraction bump magnets. 65](#__RefHeading___Toc91568098)

[Table 3.5‑2: Thick septum operational parameters for higher fields:
73](#__RefHeading___Toc91568099)

[Table 3.5‑3: Thin septum operational parameters for higher fields (SR
thin septum\*): 73](#__RefHeading___Toc91568100)

[Table 3.5‑4: Thin and Thick septum fixed parameters
76](#__RefHeading___Toc91568101)

[Table 3.5‑5: Thick septum operating parameters
76](#__RefHeading___Toc91568102)

[Table 3.5‑6: Thin septum operating parameters (SR thin septum)
76](#__RefHeading___Toc91568103)

[Table 3.6‑1: List of all mayor dc and ramped power supplies in the
booster and BTS including upgrade requirements.
95](#__RefHeading___Toc91568104)

[Table 3.6‑2: List of capability of DC cables for all mayor booster and
BTS power supplies. 95](#__RefHeading___Toc91568105)

[Table 3.8‑1: ALS Booster RF parameters as a function of η~σ~ parameter.
101](#__RefHeading___Toc91568106)

[Table 3.8‑2: Booster RF parameters for proposed energy ramp for ALS
Top-Off mode of operation. 102](#__RefHeading___Toc91568107)

[Table 3.8‑3: RF parameters for current and Top-Off mode.
104](#__RefHeading___Toc91568108)

[Table 3.8‑4: Electrical power and LCW requirements for current
installation and upgrade condition. 106](#__RefHeading___Toc91568109)

[Table 3.9‑1: Cleaning system parameters for the ALS Booster.
110](#__RefHeading___Toc91568110)

[Table 3.9‑2: ALS-like stripline kicker characteristics.
111](#__RefHeading___Toc91568111)

[Table 3.9‑3: Beam charge monitors in the ALS complex.
113](#__RefHeading___Toc91568112)

[Table 3.9‑4: Source Point 1 synchrotron radiation characteristics
115](#__RefHeading___Toc91568113)

[Table 3.9‑5: Source Point 2 synchrotron radiation characteristics
116](#__RefHeading___Toc91568114)

[Table 4.3‑1: Summary of the cost estimate for the ALS Top-off upgrade
as of November 19, 2004. 132](#__RefHeading___Toc91568115)

[Table 4.3‑2: Cost estimate down to WBS level 3 for the ALS top-off
upgrade as of November 19, 2004. 133](#__RefHeading___Toc91568116)

# Appendices

## Parameter List

### Storage Ring Performance Parameters

+-----------------------------------+-----------------------------------+
| Beam Energy                       | 1.0 -- 1.9 GeV (1.9 GeV nominal)  |
+-----------------------------------+-----------------------------------+
| Beam Current (multibunch)         | 10-500 mA (500 mA nominal)        |
+-----------------------------------+-----------------------------------+
| Number of bunches (multibunch)    | 250-320                           |
+-----------------------------------+-----------------------------------+
| Beam Current (two bunch)          | 10-60 mA (50 mA nominal)          |
+-----------------------------------+-----------------------------------+
| Bunch purity (two bunch)          | \< 10^-4^                         |
+-----------------------------------+-----------------------------------+
| Beam Current (single camshaft     | \<12 mA (10 mA nominal)           |
| bunch)                            |                                   |
+-----------------------------------+-----------------------------------+
| Bunch purity (camshaft)           | \< 10^-4^                         |
+-----------------------------------+-----------------------------------+
| Natural horizontal emittance      | \< 6.75 nm (nominal 6.3 nm at 1.9 |
|                                   | GeV, W11 closed)                  |
+-----------------------------------+-----------------------------------+
| Vertical emittance                | 10 -- 150 pm (nominal 30 pm, 1.9  |
|                                   | GeV, multibunch)                  |
+-----------------------------------+-----------------------------------+
| Beam Energy Spread                | 0.97\*10^-3^ (1.9 GeV,            |
|                                   | multibunch)                       |
+-----------------------------------+-----------------------------------+
| Bunch length                      | 20-50 ps (rms, 1.9 GeV            |
|                                   | multibunch, nominal 30 ps)        |
+-----------------------------------+-----------------------------------+
| Touschek lifetime (multibunch)    | \> 2 h (1.9 GeV, 500 mA, 6.3 nm,  |
|                                   | 30 pm)                            |
+-----------------------------------+-----------------------------------+
| Current stability in top-off      | 3\*10^-3^ (multibunch, 1.9 GeV,   |
| (typical)                         | i.e. 1.5 mA out of 500 mA)        |
+-----------------------------------+-----------------------------------+
| Typical time between injections   | 30 s                              |
+-----------------------------------+-----------------------------------+
| Stored beam transients due to     | Horiz.: \<400 μm peak for less    |
| injection elements                | than 200 μs,                      |
|                                   |                                   |
|                                   | \<50 μm peak for less than 100 ms |
|                                   |                                   |
|                                   | Vert.: \<100 μm peak for less     |
|                                   | than 300 μs,                      |
|                                   |                                   |
|                                   | \<10 μm peak for less than 100 ms |
+-----------------------------------+-----------------------------------+
| Injection efficiency              | \>60%                             |
+-----------------------------------+-----------------------------------+

### Booster Performance Parameters

  ----------------------------------- -----------------------------------
  Injection Energy                    50 MeV

  Extraction Energy                   1.0 -- 1.9 GeV (nominal 1.9 GeV)

  Number of bunches                   1-10

  Maximum Charge                      3.3 nC

  Cycle Rate                          0.005-1 Hz (nominal 0.33 Hz at 1.9
                                      GeV for initial injection, 0.033 Hz
                                      for top-off)

  Injected beam emittance             1.1 μm

  Injected longitudinal emittance     3.9\*10^-4^ eVs
  (6πσ~E~σ~τ~)                        

  Natural horizontal emittance        230 nm (1.9 GeV)

  Energy spread                       0.8\*10^-3^ (1.9 GeV)

  Bunch purity at extraction          \<10^-4^
  ----------------------------------- -----------------------------------

### Technical Parameters

  ----------------------------------- -----------------------------------
  Booster maximum bending field       1.622 T (1.95 GeV)

  Corresponding dipole current        1019 A

  Dipole power supply repeatability   0.05 %

  Booster maximum quadrupole field    19.79 T/m (1.95 GeV)

  Corresponding quadrupole current    500 A

  Quadrupole power supply             0.05 %
  repeatability                       

  Booster maximum sextupole current   10 A

  Sextupole power supply              0.1 %
  repeatability                       

                                      

  Maximum klystron RF power installed \>75 kW

  Maximum dissipated cavity cell      \<70 kW (nominal 66 kW)
  power                               

                                      

  Booster Extraction bumps maximum    0.5 T (0.47 T nominal)
  field                               

  Corresponding bump current          306 A

  Booster extraction kicker maximum   17 kV
  voltage                             

  Booster thin septum maximum field   0.38 T

  Corresponding septum current        4550 A

  Booster thick septum maximum field  1.3 T

  Corresponding septum current        5210 A

                                      

  BTS bend magnets (B1-B4) maximum    1.677 T (1.95 GeV)
  field                               

  BTS bend magnets (B1-B4) maximum    846 A
  current                             

  Power supply stability              300 ppm

                                      

  Storage ring injection bumps        7000 A
  maximum current                     

  Storage ring thin septum maximum    0.38 T
  field                               

  Corresponding septum current        5460 A

  Storage ring thick septum maximum   1.3 T
  field                               

  Corresponding septum current        5210 A

                                      

  Nominal physical aperture at        \> 15 mm
  injection point                     
  ----------------------------------- -----------------------------------

## Full Cost Estimate

November 19, 2004

![](media/image91.png){width="6.192361111111111in"
height="4.363194444444445in"}

![](media/image92.png){width="6.206944444444445in"
height="4.3590277777777775in"}

![](media/image93.png){width="6.192361111111111in"
height="4.346527777777778in"}

![](media/image94.png){width="6.198611111111111in"
height="4.354861111111111in"}

![](media/image95.png){width="6.192361111111111in"
height="4.348611111111111in"}

![](media/image96.png){width="6.192361111111111in"
height="4.346527777777778in"}

![](media/image97.png){width="6.192361111111111in"
height="2.777083333333333in"}

[^1]: The exact transfer energy is 1.522 GeV.

[^2]: As a design margin, throughout this section 2.0 GeV is assumed as
    the design energy for pulsed elements.

[^3]: Engineering Note: Light Source -- Booster Extraction Bump Magnets.
    AL0323, M6852

[^4]: G.Stover "Comparison of Booster ring \"Bump magnet\" B field
    measurements vs. calculations @ 1.522 and 2.0 Gev." ALS Top-Off
    Project Note 04/19/2004

[^5]: G.Stover "Comparison of Booster ring \"Bump magnet\" B field
    measurements vs. calculations @ 1.522 and 2.0 Gev." ALS Top-Off
    Project Note 04/19/2000

[^6]: Chart 9.4a, High Voltage Technology, L.L.Alston