Expression of Interest for the Superconducting Module & Test Facility
(SMTF)

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Institutions Involved in Discussions

Argonne Laboratory (ANL), Brookhaven (BNL), Cornell University,
Fermilab, Jefferson Laboratory (JLAB), Lawrence Berkeley National
Laboratory (LBNL), Los Alamos National Laboratory (LANL), MIT-Bates
Laboratory, Michigan State University National Superconducting Cyclotron
Laboratory (MSU-NSCL), Northern Illinois University (NIU), Spallation
Neutron Source (SNS) at Oak Ridge, University of Pennsylvania, and
Stanford Linear Accelerator Center (SLAC).

International: DESY, INFN, KEK

Contact: Swapan Chattopadhaya <swapan@jlab.org>, Helen Edwards
<hedwards@fnal.gov>, Nigel Lockyer <lockyer@fnal.gov>, or Shekhar Mishra
<mishra@fnal.gov>

1\. Executive Summary

This Expression of Interest (EOI) describes a new US initiative in
Superconducting RF (SCRF) research and development. The goal is to
strengthen capabilities in high gradient and high-Q SCRF superconducting
accelerating structures and related subsystems in support of the
International Linear Collider (ILC) and other accelerator projects of
interest to US laboratories. It is envisioned that a central test
facility, designated the "Superconducting RF Module and Test Facility"
(SMTF), will be constructed in the Meson Area by a consortium of US
laboratories and universities coordinated by Fermilab. The SMTF will
seek to complement existing and planned SCRF infrastructure and
capabilities at other U.S. laboratories. This effort should be
coordinated with the ILC-Americas and ILC international collaborations
that will develop components for the ILC main linac. The facility and
its components will be constructed in phases, roughly over the period
2005-2008.

The centerpiece of SMTF will be the SCRF cavity test facility with beam
operation capability, which will share infrastructure with three
additional areas for \< 1 and for CW (100% duty factor) cavities, in
support of other programs of interest within the U.S. (such as ILC, RIA,
Proton Driver, and 4^th^ generation light sources). Possible
collaboration with the international HEP laboratories DESY, KEK, INFN
and others is being discussed as part of the global R&D program for the
ILC. It is likely that the main ILC linacs will be constructed by all
three regions in the world. Therefore expanding present US industrial,
laboratory, and university capabilities to contribute significantly will
become essential for the success of the ILC. To this end goals at SMTF
will be to work with and integrate US industrial capabilities. The test
facility and fabrication capability will be critical to the advancement
of the ILC linac R&D effort.

The SMTF EOI is formulated with recognition of the JLab Center of
Excellence plan proposal (SRF Accelerator Science and Technology Center
plan). Discussions are underway to join these two concepts in a way that
makes best use of resources and capabilities and tries to minimize
overall projected cost.

SMTF is envisioned as:

-   A multi-laboratory collaboration on SRF development over a broad
    range of applications. The synergy of expertise will benefit all
    four areas.

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-   A facility where different module types and linac systems can be
    tested (some with beam).

-   An organization that will develop inter-laboratory collaboration
    (including non-US participation) on cold linac technology, including
    module development and fabrication. The area specific to ILC will be
    carried out under ILC direction.

-   The SMTF collaboration will have organizational boards that work
    through Fermilab management for the direction of the projects.

Four main areas planned for the program are:

1)  International Linear Collider (ILC):

    a.  Establish a high gradient, 1.3 GHz cryomodule test area at
        Fermilab with a high quality pulsed electron beam using an
        upgraded A0 injector.

    b.  Fabricate four 1.3 GHz high gradient cryomodules (eight cavities
        each) using industrial and laboratory partners in the US. The
        fabrication R&D will be carried out as a collaborative effort
        under the leadership of Fermilab for the ILC-Americas
        organization.

    c.  Test cryomodules and other rf components as fabrication and
        operation experience is acquired and designs are optimized.

2)  CW:

    a.  Fabricate the highest attainable Q-value cryomodules.

    b.  Establish a test area that will extend the reach of present US
        program in CW capabilities.

> This facility will be located in the same beam line (M-East) as the =1
> test beam to allow limited testing with the pulsed beam from an
> upgraded A0 photo injector.

3)  Proton Driver (PD): \< 1

    a.  Fabricate test structures and cryomodules for Proton Driver
        applications.

    b.  Establish an area for high power RF testing of \< 1 accelerating
        structures in pulsed mode (\~1% duty factor).

    c.  The Proton Driver also uses 1, 1.3 GHz cavities cryomodules.
        These cryomodules are nearly identical to the ILC Cryomodules.
        We anticipate an overlap in ILC and PD R&D activities in this
        area.

4)  Rare Isotope Accelerator (RIA):

    a.  Cleaning and cold-testing of individual cavities, after chemical
        processing

    b.  Clean assembly of cavities into cavity strings, forming a sealed
        assembly including RF couplers, beam line valves, and vacuum
        manifold and valves.

    c.  Assembly of cryomodules incorporating the cavity strings.

    d.  Cold test of assembled cryomodules.

Some specific program goals include:

-   Demonstrate for ILC and the Proton Driver 1.3 GHz cavity operation
    at 35 MV/m with beam currents up to 15 mA at a 1% duty factor.

-   Develop the capability to reliably fabricate high gradient and
    high-Q SCRF structures in US industry and laboratories for the
    stated applications.

-   Develop and demonstrate high gradient, pulsed mode, \<1 cavity
    operation at 1.3 GHz and 325 MHz for Proton Driver applications, and
    CW operation at various frequency cavities for the RIA project.

-   Demonstrate 20 MV/m CW cavity operation with Q values 3E10 for light
    source applications.

We propose that the SMTF test area will be constructed in the meson
experimental area at Fermilab, in phases, over the next several years.

-   Phase 1: Installation of infrastructure culminating in the RF power
    tests of a single ILC cryomodule within the 1.3 GHz, high gradient
    pulsed test area. This cryomodule will likely be provided by TESLA
    Collaboration.

> Relocation and commissioning of the Fermilab NICADD photo injector in
> the SMTF. Initiate beam tests of a single ILC cryomodule utilizing the
> photo injector.
>
> Start fabrication of a US cryomodule using a combination of
> industries, laboratories and universities.
>
> Commission the proton driver, light sources, and RIA test areas.
> Pulsed RF power tests (325 MHz) of \<1 spoke resonators and CW RF
> sources for 345 MHz RIA cavities.

-   Phase 2: Install, and operate with beam, a complete SMTF-ILC RF unit
    consisting of two high gradient cryomodules, of which at least one
    is fabricated by the ILC-Americas collaboration with industrial
    partners. This may be powered by a high power modulator and a 10 MW
    multibeam klystron if available.

> The \<1 proton driver test area and next generation light sources area
> will evolve in a similar manner to the ILC area.
>
> The proton driver \< 1 area will initially include a 325 MHz pulsed RF
> system and a test cryostat for pulsed-mode operation of RIA-type SCRF
> spoke resonators. The RIA area will initially include 345 MHz and
> other frequency CW RF systems. In later phases of operation, the
> addition of an H- source, radio frequency quad (RFQ), and
> medium-energy beam transport (MEBT) would complete a beam-capable test
> bed for LLRF and resonance control when driving low-beta ion beams
> with multiple cavities powered from a single klystron.

-   Phase 3: Install, and operate with beam, two complete SMTF-ILC RF
    units consisting of four high gradient cryomodules, two high power
    modulators and two 10 MW multibeam klystrons.

> Improve the photo injector with the addition of cryomodules of 1.3 and
> 3.9 GHz.

This Expression of Interest outlines the rough goals and scope of the
SMTF project. Ideally the SMTF would support concurrent operation of all
four areas. The SMTF should also provide a large amount of calendar
availability for each of the four programs in every year of operation we
expect that a dialog among Fermilab, the participating laboratories, and
funding agencies will commence after this report is reviewed. In
response to this EOI, the collaboration hopes to receive guidance on how
to proceed with the next steps toward a full proposal.

2\. Introduction and Motivation

A variety of projects are being planned in particle physics, nuclear
physics, and fields of basic energy sciences such as condensed matter
physics and biological physics that propose to use superconducting RF
(SCRF) linac technology. These projects are distributed across many of
the major US laboratories funded by DOE and NSF. This expression of
interest is to inform Fermilab management that we will propose to
construct a superconducting RF module and test facility (SMTF) in the
meson area at Fermilab. A medium energy electron beam and a low energy
H- beam would permit a unique opportunity for characterization of the
properties of superconducting RF cavities and for beam-related
experiments. The members of the team are from a consortium of several US
laboratories and universities.

We list several possible future projects that use RF Superconductivity.

1)  International Linear Collider (ILC)

2)  The Rare Isotope Accelerator (RIA) (located at Argonne or MSU)

3)  Proton driver at Fermilab or BNL.

4)  Upgrades (12 GeV) to JLAB electron linac, the extensions of the FEL
    and the proposed ELIC (Electron Light Ion Collider)

5)  SNS (Spallation Neutron Source) upgrades to higher beam power \~ 4
    MW.

6)  Fourth generation light sources at ANL, BNL, Cornell, JLAB, LBNL,
    and MIT using SCRF linac technology for ERLs (energy recovery
    linacs) or FELs (free electron lasers).

7)  Brookhaven plans to use ERLs for electrons colliding with RHIC heavy
    ion beams (E-RHIC) and for electron cooling of the RHIC beams.

These projects have common or similar rf systems and require development
that would benefit from a coordinated effort among the laboratories.
Several of the laboratories have infrastructure to carry out SCRF
development but have limited fabrication capabilities. The current
efforts in SCRF are broadly funded by USDOE HEP, Nuclear, Basic Energy
Sciences and the NSF. Many of the above projects would benefit from a
cryomodule test facility with beam capabilities, which is presently not
available in the US. We propose such a facility and refer to it as the
SMTF. It would fill the gaps in the existing SCRF development
capabilities.

The critical tests that groups from the above projects could perform at
this facility include:

1)  Demonstrate for ILC 1.3 GHz cavity operation at 35 MV/m with beam
    currents up to 15 mA at a 1% duty factor in two cryomodules with 8
    cavities each.

2)  Demonstrate for CW applications 20 MV/m cavity operation at Q values
    \> 3E10.

3)  Demonstrate for the Proton Driver 1.3 GHz, \~ 0.5-0.8, elliptical
    cavity operation at \> 15 MV/m at Q \> 5E9 and a 1% duty factor with
    multiple cavities being driven by one klystron.

4)  Demonstrate for the Proton Driver and related applications high
    gradient operation in pulsed mode of 1.3 GHz and 325 MHz, \< 1
    cavities and cryomodules.

5)  Demonstrate individual cavity resonance control with multiple
    cavities driven from one klystron, using fast ferrite phase
    shifters, at both 1.3 GHz and 325 MHz

6)  Demonstration of RIA cavities and cryomodules.

These demonstrations encompass research and development topics critical
for the continued iteration and evolution of SCRF linac systems, for the
development of cost effective low to medium linac sections needed for
proton/ion linacs, and development of lower power cost (driven by
refrigeration costs) CW operation for the many upcoming light source
applications and for the future ILC.

Thus the SMTF goals are to:

-   Collaborate on SRF technology development including industrial
    collaboration

-   Provide a structure for SRF module and systems design evolution and
    fabrication

-   Provide a test environment and infrastructure for module and linac
    systems test and evaluation

3\. The JLab Accelerator Science & Technology Center Plan (ASTC) and the
SMTF Plan

JLab has been asked by the DOE Office of Science to provide a
progressive plan for improving US SRF capabilities. It is important to
have a concept of how this plan and SMTF could merge to a consistent
picture.

The JLab plan addresses three capability levels:

-   Near Term needs (RIA, 12GeV Upgrade)

-   Capability for design and delivery other SRF systems (exclusive of
    LC) in collaboration with partners

-   Construct an integrated cryomodule prototype production plant with
    focus on LC and the need for industrial technology transfer.

This last effort has significant cost associated with it.

Discussion is underway among the interested labs how to implement
initial activities. This SMTF EOI is a start in that direction.

In the longer term, substantial investment in SRF capability for the ILC
will be necessary in order to get to a state of preproduction capability
and industrial technology transfer in the US. Just what will eventually
be needed for this long term goal needs careful planning and analysis,
as the facilities could be a major investment and every effort should be
made to minimize costs while accomplishing the development toward
industrialization goals necessary for an ILC.

A model is under discussion where the two plans (ASTC and SMTF) could
mesh and utilize the strengths of the two major player labs in the
module development, JLab and FNAL. It would also be important to
integrate the SCRF capabilities and infrastructure that exists in labs
such as LANL, MSU, Argonne and Cornell. Industrial participation in
these activities and planning for industrialization can be developed.
The synergy of SCRF expertise in the US would greatly strengthen the
activities. Certainly it is clear that pre-industrial capability should
be developed with a coherent plan that uses and builds on existing
laboratory strengths. Equally clear is the importance of individual US
labs having and developing their SRF capabilities on a scale compatible
with R&D on the smaller than pre-industrial scale. The large scale of
the ILC effort calls for a combination of the existing strength of the
US SCRF community.

**4.** Proposed SMTF Plan

We propose to develop the meson east area at Fermilab into a cryomodule
test area. The document is organized around the three main SCRF areas:
the 1.3 GHz,  ILC Cryomodule test facility, the CW test area for
next-generation CW light source, and the \< 1 test area for PD, and the
RIA facility. These R&D activities will operate under a shared
infrastructure of the Meson cryogenic facility, pulsed rf and modulator
power sources, controls, safety and technical support.

The allocated space should be able to accommodate initially three test
areas. The high gradient pulsed work and the CW activities would be
located in a single 100-150 meter beam line. A second area would be
large enough to accommodate the 325 MHz \< 1 cryomodule activities. We
anticipate three different communities using the facility. At the same
time these communities will have strong interactions to benefit all four
areas. One community will concentrate on 1.3 GHz pulsed high gradient
tests, such as needed for the ILC and Proton Driver. Another community
will focus on cryomodule operation needed for the fourth generation
light source and FEL accelerators that use high Q, CW operation. The
third community will emphasize \< 1 activities at various rf
frequencies. We envision that the regions will initially operate in two
different modes. In one region, physicists would perform high power
cryomodule tests as well as beam tests with a medium energy electron
beam (40 - 300 MeV). This is the energy of the injector into the first
spectrometer. We would also develop a beam analysis section downstream
of the cryomodule. In the parallel region, tests (initially without
beam) could be ongoing with low beta demonstration cryomodules.
Shielding between the two regions will be necessary for flexible
operation. The details of the layout are still being worked out.

The electron beam test area in SMTF would consist of an electron beam
injector, a beam analysis region after the injector and before the
cryomodules in order to measure incoming beam properties, a section of
up to four cryomodules, which constitutes two ILC RF units (defined
later), and space afterwards to evaluate the outgoing beam properties.
The CW activities are located downstream of the ILC cryomodules. The
existing Fermilab FNPL (A0 injector) would be an appropriate initial
source. To achieve 40-300 MeV will require an upgrade to the source as
described later. This consists of a gun and accelerating section, and is
about 15 m (upgraded eventually to 25 m) in length. We estimate that 20
m of beam analysis space is needed to measure beam properties, followed
by space for four 12-17 m cryomodules, and an additional 20 m of
analysis space for the outgoing beam and a beam dump, for a total of
100-150 m.

The cryogenics plant in the meson area needs an upgrade. We propose a
two step approach. For the first step we make minimal modifications to
the existing infrastructure and utilize what we can to supply the area
quickly with about 60 Watts of refrigeration at 2K. Each TESLA Test
Facility (TTF) cryomodule (eight 9-cell cavities) consumes about 19
Watts of refrigeration at 2K. The third step will requires a new
refrigeration plant that can handle \~300 Watts. The cryogenics are
described in Appendix II. Medium energy electron beams will be used for
testing the cryomodules in the area and dark currents should be expected
from the cavity modules, therefore the appropriate radiation shielding
will be necessary.

To get started quickly we propose to initially use an eight cavity
cryomodule that was produced for the TTF. We expect that the TESLA
collaboration will provide this cryomodule. In parallel, we would
aggressively move to construct cavities, auxiliary components (power
couplers, HOM couplers, tuners, helium vessels), and cryomodules in the
US. We note that US industry considerably lags European industry in SCRF
technology and our plans would help correct this situation. This is
especially desirable given the large number of SCRF projects in the US,
and the large scale of the ILC. We also note that significant
infrastructure exists at US laboratories and will need upgrading. We
plan to incorporate existing infrastructure and expertise at US labs and
universities as well as US industry to build cavities, carry out bare
cavity tests in vertical Dewars, perform dressed cavity horizontal
tests, and assemble cavity strings and cryomodules. In addition we would
build couplers and tuners and other cryomodule components to extend the
full range of expertise and technology required for the major projects
envisioned.

In Phase I it is expected that ILC-Americas, Proton Driver, RIA, CW and
interests will launch independent but collaborative activities to build
cryomodule(s). Individual laboratories would assume responsibility for
major subsystems and pre-testing efforts. This EOI proposes that, with
coordination from the ILC-Americas collaboration, Fermilab will lead the
effort of fabricating and testing the ILC and PD cryomodule and ANL will
lead the RIA cavities testing and production work. The leadership of CW
cryomodule fabrication for light source applications is not yet
established. See Appendix III for more details on cavity and cryomodule
fabrication and testing infrastructure that will be required of such a
facility.

This document is organized around the four main SCRF areas: 1.3 GHz and
= 1, CW, \< 1 for Proton Driver and RIA programs. Even though we present
the four research concentrations separately for ease of reading, the
resources and goals significantly overlap. Each area will benefit from
the collaborative effort.

5\. 1.3 GHz Fabrication & Test Facility Program

We plan to proceed with three main phases in the development of an ILC
module test bed (See Figure 1.). This section describes these three main
phases.

An ILC rf unit will eventually need to be defined for both the 500 GeV
and 1 TeV ILC designs. In our discussions, we are moving towards an ILC
cryomodule with 35 MV/m, 1.3 GHz cavities for both 500 GeV and 1 TeV
operation. The power sources currently being developed can provide 10 MW
of RF power so it is natural to define an RF unit as the number of
cavities powered by such a source (i.e., one modulator and one
klystron). Given the state of cryomodule development and the desire to
have some overhead in choosing the ILC beam current, we define an
SMTF-ILC rf unit for test purposes as two cryomodules with eight
TESLA-like (9 cell) cavities each. Assuming 6% rf transport losses, each
cavity in the rf unit could be powered up to 530 kW with a 10% overhead.
At 35 MV/m, a 15 mA beam could be accelerated, which is about 15% more
current than in the TESLA 800 design. We note that our present concept
for the ILC cryomodule is based on the TESLA Test Facility (TTF) design,
which contains eight nine-cell cavities. It may be cost effective for
the ILC to have 12 nine-cell cavities per cryomodule as was proposed and
costed for the TESLA Technical Design Report (TESLA TDR).

1\) We propose to bring into operation one cryomodule with the goal of
demonstrating 35 MV/m cavity operation. It is expected that it may take
more than one module iteration to achieve this gradient.

The A0 photo injector[^1] will be moved, installed and recommissioned
with the cryomodule (step 1) in order to perform beam measurements,
which are discussed below.

We will initiate beam tests of a single ILC cryomodule utilizing the
photo injector.

2\) We will bring into operation one SMTF-ILC rf unit, defined as two
cryomodules each containing eight 9-cell cavities, one high power
modulator, one 10 MW multibeam klystron and perform beam measurements.

The injector will be upgraded to include the Fermilab built 3.9 GHz
accelerating and deflecting cavities.

3\) We propose to bring into operation two SMTF-ILC rf units and
associated rf power, instrumentation and controls.

We also envision an upgrade of the injector to use eight 1.3 GHz
cavities and four 3.9 GHz cavities in cryomodules. This would also
enable us to perform accelerator physics measurements.

These three phases will allow for iteration of component and integrated
linac systems designs as they evolve toward final industrial prototypes.
They will allow investigation and iteration of beam and accelerator
measurements. Though these steps are closely aligned with similar
activities at TTF, we believe it is imperative for a project the size of
ILC that each region carries out fundamental developments of the large
systems, such as the linac[^2]. The ILC test bed at SMTF would allow for
certification of cavity performance, testing with different klystrons,
couplers, and low level rf (LLRF) systems, and the study of performance
under different beam loading conditions as well as measurements of beam
properties. The SMTF might also act as the main database for these test
results.

The preliminary outline of time scale for the three phases described
above is 1) 2005-2006, 2) 2006-2007, 3) 2007-2008. The timeline has been
developed to coincide with ILC goals and is expected to evolve.

The injector and its upgrade are described later in this document and in
detail in Appendix I.

![](media/image2.png){width="6.488194444444445in"
height="4.843055555555556in"}

Figure 1. Phases of the SMTF 1.3 GHz test facility.

In phase 1, we want to first establish operation of a TESLA
Collaboration and/or 1^st^ US cryomodule at some intermediate gradient
in order to establish our abilities with the technology. We would then
establish high gradient performance along with Q and dark current
measurements without beam. Tuner tests with the cryomodule would be
performed to establish the necessary specification. Beam commissioning
could proceed after the static tests were complete.

We believe it is important to follow a parallel path of constructing and
processing new cavities and cryomodules in the US. The first cryomodule
fabrication and testing might be divided into four major steps as
outlined below. Different labs might be given responsibility for these
different activities based on their capabilities. As an example
scenario, we consider the fabrication processing and component testing
of US 1.3 GHz cryomodules in five stages.

First stage: Bare Cavity (working with industrial partners.)

1)  procure and verify pure niobium

2)  construct =1 cavities,

3)  tune the cavities,

4)  apply chemical processing,

5)  bake cavities

6)  repeat chemistry

7)  high pressure rinse (HPR)

8)  vertical dewar test

Requires: chemistry, vertical dewar, shielding, low power rf, cryogenics

Second stage: Dress Cavity

1)  attach helium vessel

2)  check tune

3)  re-acid etch and HPR

4)  dress for horizontal cavity test

5)  perform horizontal cavity test

Requires: chemistry, horizontal module, shielding, low power rf,
cryogenics

Third stage: Components

1)  acquire cryostat components

2)  acquire rf power source and wave guides

3)  input coupler fabrication, clean assembly and conditioning

Fourth stage: String Assembly

1)  re-clean for string assembly

2)  string assembly

3\) acquire parts for string: magnets, BPM, gate valves, bellows, cold
input coupler, etc

Requires: chemistry, large clean room for assembly

Fifth Stage: Module Assembly

1)  prepare cold mass

2)  assemble string to cold mass

3)  mount warm couplers

4)  install into cryostat for testing

Requires: large industrial space, cold mass parts, string, warm input
coupler, magnetic shielding, tuner

Sixth Stage: Module Testing

1\) Prepare and test cryomodule with beam

Also needed for this fabrication and future R&D:

1\) Electro-Polishing R&D

2\) Cryomodule test area infrastructure development

5.1 Power for Two Complete RF units (steps 1-3)

The power system at the facility will need to accommodate two complete
1.3 GHz rf units (each unit contains two eight-cavity cryomodules). Each
rf unit is nominally powered by one 10 MW klystron and modulator. These
klystrons will likely be purchased from one or more of the three vendors
(Thales, CPI and Toshiba) that DESY has contracted to develop such
tubes. These vendors have produced prototype 10 MW tubes but none has
yet performed at the level required for the SMTF. The development of
these tubes by DESY will likely continue, especially as they will
probably be used for the DESY-based XFEL project as well. In the
meantime, FNAL owns commercial 5 MW tubes that could be used instead
(one per cryomodule). Specifically, they have a Thales 2104 klystron
that is a spare for the A0 injector and they recently acquired six
Thales 2095 tubes that were originally at LANL (5 were in operation
there). It is anticipated that, with coordination from the ILC-Americas
collaboration, SLAC will lead the ILC rf power source efforts, and
source development and testing will be carried out there as well.

Two modulators for SMTF are currently under construction at Fermilab.
These are designed specifically to power any of the following: the 10 MW
1.3 GHz multi-beam klystrons from Thales, CPI, or Toshiba; the 325 MHz
JPARC/Toshiba klystron planned for the \< 1 linac, or the commercial
5 MW, 1.3 GHz klystrons. The modulators can be reconfigured to support
pulse widths of 1.5 msec for ILC and 3 msec or 4.5 msec for the Proton
Driver.

5.2 Cryogenics Needs

The cryogenic need for phase 1, 2 and 3 at 5 Hz are 30, 80 and 130
watts, respectively, at 2 degrees K as described in detail in Appendix
II. The meson cryogenic plant can provide up to 60 watts at 2 deg K. We
propose to operate the cryomodule at a lower repetition rate for phase 2
and for phase 3 until the cooling capability is increased as discussed
below. In the meson cryogenic system there are three thermal shields,
operated at 2.0K, 4.5K, and 80K. The 80K shield will be liquid nitrogen,
the 4.5K shield is gaseous helium, and the 2.0K shield is super-fluid
helium.

Other items that will be needed are the phase separators, control
systems, vacuum pump (sub-atmospheric to lower temperature to 2 K.),
transfer lines, and a feedbox. The feedbox contains a low pressure heat
exchanger, numerous control valves, instrumentation and must connect to
cryomodules via an input cryogenic feed cap. A cryogenic end cap will be
needed.

Care in avoiding contamination of the helium is necessary because the
system is running at a sub-atmospheric pressure. This implies that
regular maintenance for decontamination will be necessary.

One additional requirement for phase 3 is that the cryogenic
distribution must feed the cryomodule and the three connections to the
A0 photo injector. Three additional smaller feedboxes will be
constructed.

The time needed to install the cryogenic distribution system is about 6
months. The feedbox will require about 9-12 months to complete.

For 5 Hz operation of the 2 rf units, a larger cryogenic system will be
required. The long-lead item for phase 3 is a \~300 Watt, 2 K
refrigerator where it is estimated that it will take two years to
acquire. There are at least two companies that can build this unit and
possibly others. It is desirable that we place an order as soon as
possible.

See Appendix-II for a more detailed discussion of the cryogenic system.

5.3 Measurement and Tests

5.3.2 Electron Beam Tests

We outline below possible studies with an electron beam for the SMTF.
First, the rf performance of the cavities can be measured directly with
beam and secondly, the impact of the cavity on the beam can be assessed.
An initial set of measurements would include:

-   Beam energy: a spectrometer would provide an independent and
    accurate measurement of the accelerating gradient (rf based
    techniques are not as accurate).

-   Long-range wake-field characterization: Measure frequency spectra of
    bunch positions downstream of cryomodule to search for high Q cavity
    dipole modes that could cause beam break-up in the ILC. Correlate
    these data with HOM power measurements.

-   Tests of low-level rf system: demonstrate that a \< 0.1%
    bunch-to-bunch energy spread can be achieved in a 1 msec bunch
    train.

-   Impact of the SCRF cavity on transverse beam dynamics: measure the
    beam kicks caused by the fundamental mode fields.

-   Study beam centering based on HOM dipole signals.

> To study basic cavity performance during beam operation, the injector
> at SMTF should provide bunch trains comparable to those envisioned for
> the ILC. The main requirements include:

-   bunch charge: up to 2e10 electrons

-   bunch length: as low as 300 microns rms bunch spacing: nominally 337
    ns with option of halving this.

-   bunch energy stability \< 1% rms average

-   current stability \< 1% rms (preferably \< 0.1% rms)

-   number of bunches: up to 2820

-   pulse rep rate = up to 5 Hz

> This broad range of measurements will present several technical
> challenges, the details of which have to be worked out.

5.3.3 Other Studies:

-   Determine the maximum operating gradient of each cavity & its
    limitations.

-   Evaluate gradient spread and its operational implications.

-   Measure dark currents, cryogenic load, dark current propagation, and
    radiation levels.

-   Measure alignment of the quadrupole, cavities and BPM in-situ using
    conventional techniques (e.g. wire or optical).

-   Measure vibration spectra of the cryomodule components, especially
    the quadrupole magnet.

-   Measure system trip rates and recovery times to assess availability.

-   Develop LLRF exception handling software to automate system and
    reduce downtime.

-   Evaluate failures with long recovery times: vacuum, tuners, piezo
    controllers, and couplers.

5.4 Photo Injector Upgrade

5.4.1 Three Possible Upgrade Plans

The A0 photo injector will be moved to SMTF and will be upgraded in a
phased approach. The present plan at A0 is to reconfigure the injector
to include: a normal conducting gun, and two Tesla cavities (one
operating at 12 MV/m and one at 25 MV/m). This configuration requires a
high power klystron/modulator system (\~4-5 MW) for the normal
conducting gun, and two low power systems (\~300 KW nominal each) for
the two Tesla cavities. The high power modulator system is very similar
to that discussed above for a 10 MW klystron. The main difference is the
multi-beam klystron with its higher efficiency. The multibeam klystron
can supply higher output power than a conventional single beam klystron
when either is powered by the same modulator. Both the gun and the
modulator would need to be upgraded for 5 Hz long pulse operation.

A further step would incorporate two 3.9 GHz cavities of two different
designs, presently under development. One of these cavity types (3^rd^
Harmonic) is operated in deceleration mode and linearizes the beam bunch
energy with time. The other operates in a deflecting mode and is used as
a diagnostic to measure beam properties within the different time slices
of the beam bunch. The cavities require \~4 KW power. To implement these
two cavities requires two additional low power modulators; one of which
is similar to that needed for the individual TESLA cavities (above), and
one that is a gated CW modulator.

![](media/image3.png){width="5.999305555555556in" height="3.275in"}

Figure 2 Upgraded Photo injector

Eventually it might be desirable to upgrade the injector to a system
similar to that now at TTF. The two TESLA cavities would be replaced by
an eight cavity module with some of the cavities operating at \~12MV/m
and the rest at\~25 MV/m. Alternatively the module could be in addition
to the two cavities, and installed downstream of them. This module would
require a high power (5 MW) klystron/modulator system. The one 3.9 GHz
decelerating cavity would be replaced by a module of four 3^rd^ Harmonic
cavities and would require an 80 KW klystron that could actually be the
same unit as before, but operated at higher power.

We plan to expand the infrastructure at Fermilab to have the ability to
make measurements on "bare" 3.9 GHz cavities in collaboration with
Argonne. A test system will require space for a vertical Dewar and
possibly a horizontal single cavity test cryostat. These will be needed
to accomplish measurements on both bare and dressed cavities. We plan to
adopt the DESY Dewar and cryostat designs[^3]. See appendix-III for a
more detailed discussion.

5.5 SMTF RF Systems Table

+-------+-------+----------+---------+---------+---------+----------+
| S     | Phase | Cavity   | K       | K       | Mo      | M        |
| ystem |       |          | lystron | lystron | dulator | odulator |
|       |       |          |         | status  |         | status   |
|       |       |          | nominal |         |         |          |
|       |       |          | power   |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+
| One   | 1,    | 8 cavity | Thales  | exists  | "Big"   | Under    |
| M     |       | module   |         | \\spare |         | f        |
| odule |       |          | TH2104C |         |         | ab/parts |
|       |       |          |         |         |         | procure  |
|       |       |          | 5 MW    |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+
| Inj   | 1     | NC gun   | Thales  | Exists  | "Big"   | exists   |
| ector |       |          |         |         |         |          |
|       |       |          | TH2104C |         |         | needs    |
|       |       |          |         |         |         | upgrade  |
|       |       |          | 5 MW    |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+
|       |       | Tesla    | P       | Exists  | "Small  | exists,  |
|       |       | cavity 1 | hillips |         | 1"      | planning |
|       |       |          |         |         |         | to       |
|       |       |          | YK 1240 |         |         | rebuild  |
|       |       |          |         |         |         |          |
|       |       |          | 300KW   |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+
|       |       | Tesla    | P       | exists, | "Small  | under    |
|       |       | cavity 2 | hillips | under   | 2"      | f        |
|       |       |          |         | rebuild |         | ab/parts |
|       |       |          | YK 1240 |         |         | procure  |
|       |       |          |         |         |         |          |
|       |       |          | 300KW   |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+
|       |       | 3^rd^    | CPI VA  | In      | "Small  | under    |
|       |       | Harmonic | 908K2   | fabr    | 3"      | f        |
|       |       |          |         | ication |         | ab/parts |
|       |       |          | 80 KW   |         |         | procure  |
+-------+-------+----------+---------+---------+---------+----------+
|       |       | 3.9GHz   | CPI VKC | Exists  | " CW"   | under    |
|       |       | Def      | 7810F   |         |         | fab      |
|       |       | (CKM)    |         |         |         |          |
|       |       |          | 3KW     |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+
| 2     | 2     | 2, 8     | 10      | New     | "Big"   | New      |
| Cryo- |       | cavity   | MWatts  |         |         |          |
| mo    |       |          |         |         |         |          |
| dules |       | Cr       |         |         |         |          |
|       |       | yomodule |         |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+
| inj   | 2     |          |         |         |         |          |
| ector | same  |          |         |         |         |          |
|       | as 1  |          |         |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+
| 4     | 3     | 4, 8     | 10      | New     | "Big"   | New      |
| Cryo- |       | Cavity   | MWatts  |         |         |          |
|       |       |          |         |         |         |          |
| mo    |       | Cr       |         |         |         |          |
| dules |       | yomodule |         |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+
| Inj   | 3     |          |         |         |         |          |
| ector | same  |          |         |         |         |          |
|       | as 2  |          |         |         |         |          |
|       | with  |          |         |         |         |          |
|       | up    |          |         |         |         |          |
|       | grade |          |         |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+
| Inj   | 3     | 8 cavity | Thales  | need or | "Big"   | Need     |
| ector |       | module   |         | use     |         |          |
| up    |       |          | TH2104C | TH2095A |         |          |
| grade |       |          |         |         |         |          |
| 1.3   |       |          | 5 MW    |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+
| Inj   | 3     | 4 cavity | same RF | may     | same    |          |
| ector |       | 3^rd^    | as      | need    | mod as  |          |
| up    |       | Har      | before  | 2^nd^   | before  |          |
| grade |       | 3.9GHz   |         | K       |         |          |
| 3.9   |       | module   | CPI VA  | lystron | "Small  |          |
|       |       | replaces | 908K2   |         | 3"      |          |
|       |       | single   |         |         |         |          |
|       |       | cavity   | 80 KW   |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+
| spare |       |          | Thales, | 6 units |         |          |
|       |       |          | T       |         |         |          |
|       |       |          | hompson | mod     |         |          |
|       |       |          |         | anode   |         |          |
|       |       |          | TH      |         |         |          |
|       |       |          | 2095A   |         |         |          |
|       |       |          |         |         |         |          |
|       |       |          | \~5 MW  |         |         |          |
+-------+-------+----------+---------+---------+---------+----------+

6\. CW, =1 Test Facility and Program for Next-Generation Light Sources

# 6.1 Introduction

Superconducting RF structures operated in CW mode have advantages in
providing high accelerating gradients, extremely stable RF fields,
inherently small perturbative effects on the beam, and with RF power
requirements considerably less than equivalent normal conducting
structures. Taking advantage of advances made in superconducting RF
technology in recent years, several proposals have been developed for a
variety of applications of CW SCRF, including free electron lasers,
energy recovery linacs (ERL's), recirculating linacs, and beam
conditioning devices such as harmonic cavities for manipulation of
longitudinal phase space, and transverse deflecting cavities.

The high quality factor of superconducting structures (Q~0~ \~ 10^10^)
results in a very long filling time of 2.4 s for unloaded 1.3 GHz
structures, and very small intrinsic bandwidth (≈ Hz) for stable
operation. Over-coupling the cavity to the RF power input port reduces
the quality factor to a low external Q (Qext) and decreases the filling
time, but requires additional RF power to overcome reflections
introduced at the coupler. In some applications the beam loading
requirements provide a strong reason to lower the Q of the cavity
resonance such that input conditions closer approximate a match to the
beam loading. But for many applications where the system is not heavily
beam loaded, significant over-coupling has a direct consequence in
increased RF power costs. In such cases then, the coupling and the
filling time are limited primarily by the ability to provide feedback of
the system against field fluctuations induced by microphonics. For
example, a 50 Hz cavity/feed system bandwidth results in an external
quality factor Q~ext~ of 2.6x10^7^ for 1.3 GHz, multicell cavities and
the cavity filling time is then several milliseconds. Typically, power
is applied to pulsed standing wave cavities for about three time
constants before the beam enters the structure, to allow time for energy
to build up in the cavity so that the required field can be developed.
The applications of interest discussed here require bunch rates
significantly exceeding the capabilities of a system with 1-10 ms time
constant, and the superconducting linac must be operated in continuous
wave (CW) mode. The resultant power dissipation due to RF currents on
the cavity inner surfaces increases significantly over the pulsed design
parameters, for example a TESLA cavity operating at 20 MV/m CW
dissipates approximately 40 W at liquid helium temperature, compared
with \~ 1 W for the nominal pulsed operating mode (at about 1% duty
factor). Operating in CW mode at a gradient of up to 20 MV/m requires
development and testing of systems to accommodate the large thermal
load.

Application of CW SCRF in such facilities drives advances in a broad
range of accelerator communities, including synchrotron light
facilities, free-electron lasers (FELs), electron-ion colliders, and
nuclear physics facilities. Recirculating linacs and ERLs, driven by CW
SCRF linacs, are proposed advanced accelerator-based x-ray sources that
allow high peak and average brilliance, high temporal and spatial
coherence, and ultra short light pulses covering wavelengths from
infra-red to x-rays, depending on the beam energy. Using stable beams
from a CW SCRF linac allows utilization of the very low 6-dimensional
electron beam emittance produced in high-brightness electron sources --
a significant advantage over storage ring beam quality which is limited
by stochastic effects (quantum emission, intra-beam scattering,
radiation damping).

ERLs also allow high average photon flux by using very high beam power
(high bunch rate) and recovering the beam energy. Energy recovery is
achieved by passing the electron beam following acceleration and x-ray
production, back into the linac in the opposite phase to the accelerated
beam. The energy in the electron beam is deposited into the SCRF
cavities, building field for acceleration of fresh beam from the
electron source, and providing enormous savings in electrical power.
There have been several demonstrations of the ERL technique, most
recently at JLAB up to 1100 kW average beam power has been recovered in
an ERL by recirculating 7.5 mA of beam current, and up to 9 mA average
beam current has been recirculated

LBNL and MIT are developing accelerator concepts based on proposed
developments of the TESLA technology into the CW operating mode. These
facilities are designed for high peak x-ray flux and brightness from
FELs using high-quality electron beams accelerated in CW SCRF linacs,
either recirculating or single-pass.

Cornell and TJNAF are developing light sources based on x-ray production
by spontaneous emission in insertion devices with high coherence
achievable from high-brightness electron beams, and using an ERL to
achieve high average power. Cornell for example is conducting a study
towards a 100 mA, 5 GeV beam with the equivalent of 500 MW of power. At
BNL a high-current ERL for electron cooling of the RHIC beams is under
development, with the aim providing of Ampere-scale beams using a
superconducting linac.

Several RF structures are being developed for CW applications, at
different frequencies and with different parameters, but with similar
and some key overlapping issues to be addressed. A number of facilities
are currently operational and active in research and development of CW
SCRF for application in specific projects for light sources and nuclear
physics facilities, and a number are in the proposal stage. Existing
experimental capabilities include facilities at Cornell, BNL, and TJNAF.
R&D interests in application of CW SCRF include:

-   Demonstrate high gradients in CW operations \~ 20 MV/m

-   Demonstrate high Q values in CW operations. One goal, with most
    relevance to multi-GeV linac applications, is Q~o~ \> 3x10^10^

-   Demonstrate high external Q values at operating gradients of \~20
    MV/m, with a goal of Q~ext~ \> 1x10^7^ for low beam loading
    applications

-   Demonstrate high stability and control of microphonics, with a goal
    of phase error \< 0.1° and amplitude error \<10^-4^

-   Demonstrate wakefield suppression and stable operations with
    realistic beam parameters (strongly dependent on application)

6.2 Goals for a CW SCRF test facility

Existing R&D facilities mentioned above are already addressing many of
the outstanding and pressing questions in application of CW SCRF in
particle accelerators. The SMTF would provide for experimental study of
aspects of cryomodule performance not specifically addressed by other
programs. The SMTF goals may be specifically identified as demonstration
of the following:

-   High Q values in CW operations at 20 MV/m, goal of Q~o~ \> 3x10^10^

-   High stability and control of accelerating fields, goals of phase
    error \< 0.01° and amplitude error \<10^-4^

-   The above performance in the presence of electron beam of 1 nC
    charge, repetition rate \~ 10 kHz

The more demanding phase stability of 0.01° presents a challenge not
addressed at other facilities, and the presence of a CW test area in the
SMTF would allow experimental investigation of CW SCRF cryomodules to
address this and other issues listed above. The cryomodule and cavities
may be constructed in US industry, and processed and tested using
existing infrastructure at US labs.

The above goals encompass research and development topics critical for
the development of CW operation for many proposed applications.
Continued development of SCRF for CW applications will also need to
address the following major issues, especially when related to
supporting high beam current. The 1.3 GHz cryomodule tested at SMTF can
be subsequently tested at higher beam currents at Jlab or at Cornell.

The first tests at SMTF can also address some of the following issues:

-   Thermal management for a range of projected Q values

-   HOM damping validation

-   Cavity tuning control

-   Power coupler designs

Equipment will be required to allow determination of cavity Q values,
gradient, stability, HOM characteristics, thermal load at a variety of
locations within the cryomodule, input power, dark current, etc.

In addition couplers and tuners and other cryomodule components would be
fabricated to extend the full range of expertise and technology required
for the major projects envisioned.

Capabilities of the SMTF to facilitate future operation of a CW test
stand would include ability to explore high gradient CW performance
along with Q and dark current measurements without beam. Tuner tests,
HOM measurements, and cavity microphonic tuning feedback systems test
with the cryomodule would be performed to establish the necessary
specifications.

Average beam power requirements are modest, 1 nC at 10 kHz, and would
require an RF photocathode source. Beam tests will be important to
demonstrate the performance goals as outlined above, under realistic
beam conditions.

## 6.3 A prototype CW cryomodule for SMTF

The multi-cell cavity for the ILC, at 1.3 GHz, offers an existing design
which has parameters suitable to application in CW mode to meet the
needs of future facilities with modest beam loading (\~ 10 µA). To take
advantage of developments to date in SCRF, use of the cavity design
developed for ILC would provide a suitable prototype to address the
performance questions listed above for CW operations. These particular
questions are not being addressed at other facilities, and the SMTF
would provide a location and infrastructure for development of CW SCRF
systems specific to these needs, and complementary to the existing
facilities and R&D programs. Strong intellectual and technical
interactions between CW and ILC enthusiasts (many of whom are the same
people) would be of benefit to both communities.

6.3.1 Thermal management

The dynamic heat load in the CW SCRF cavities is inversely proportional
to the cavity unloaded Q value, Q~0~. Development of high Q cavities,
Q~0~ \> 3x10^10^ has significant advantages to CW operations,
particularly for larger, multi-GeV, linacs.

Lowering the temperature to 1.8 K increases the theoretical Q reachable
to more than 6 x10^10^. Allowing for a reduction by a factor of two due
to residual losses, a target of 3x10^10^ would reduce the dynamic heat
load to 13 W/m. Excellent magnetic shielding will be necessary to screen
the earth's field down to about one mGauss. (The earth's field flux
quanta get trapped in the niobium walls, due to the presence of
imperfections, impurities and oxides, thereby limiting the Q-value).

Operating at 1.8 K to reduce the BCS resistance and increase the
theoretical maximum Q-value will demand larger pumps to reach the lower
helium vapor pressure corresponding to 1.8 K. Even though the goal is to
reach a Q of 3x10^10^, a CW SMTF module should be equipped with features
to handle Q values down to 10^10^, so that we may learn how to deal with
high heat loads, if the high Q's aimed for are not realized, or
partially realized.

A cavity operating in CW mode at 20 MV/m with a Q~o~ of 1x10^10^ may be
expected to generate approximately 40 W heat load at 2 K as a result of
RF current flow on the inner surfaces of the cavity. Added to this is
approximately 8 W heat entering the cavity niobium body from the input
RF power coupler. This dynamic heat load is to be transferred through
the niobium to the cavity outer surface in the super-fluid helium liquid
bath, then to the super-fluid helium surface where boiling occurs at 1.8
K, without quenching the cavity. In a super-fluid helium test bath there
is no problem transferring this heat from the cavity outer surface to
the super-fluid helium surface, however, the transport of about 50 W
from the cavity outer surface through the helium tank, the feed-pipe and
the header-pipe requires careful engineering.

In order to provide sufficient heat transfer from the cavity outer
surface to the surface of the liquid in the header, the following
cryogenic module design issues are to be addressed:

-   The number of feed pipes between the RF cavity helium tank and the
    two-phase helium stand pipe

-   The location of the helium feeds on the helium tank

-   The inside diameter of the helium tank relative to the cavity outer
    diameter, to control the spacing between the cavity convolutions and
    the cavity helium tank inner wall through which heat must flow

-   The diameter of the liquid helium feed pipes from the stand-pipe to
    the tank

-   The diameter of the two-phase helium header pipe

Lower frequencies also reduce the BCS resistance of a cavity, and other
laboratories are pursuing designs based on lower frequencies. This work
would be complementary to SMTF.

6.4 Control of cavity HOM's and wakefields

For high average power operations, cavity Higher Order Modes (HOMs) may
present significant problems due to the perturbative effects of the
wakefields persisting from one electron bunch to the next.

Since the SCRF cavities require very smooth boundaries and transitions,
HOM damping devices are located at the ends of the cavities, in the beam
pipe, and may be in a cold section of the cryomodule or external in a
warm section.

Effective HOM damping is required to reduce beam impedance, raise
coupled-bunch instability thresholds (Beam Break-Up or BBU), and allow
stable operations.

Although the majority of these tests can be meaningfully conducted at
high average current facilities, beam tests planned with the SMTF CW
beam (1 nC, 10 kHz) would help validate bench measurements of modes and
Qs. These results would be useful input to beam stability assessment for
various applications at higher currents.

6.4.1 Feedback control of cavity tuning variations

A significant problem for the use of superconducting cavities is the
fact that systematic as well as random tuning errors are orders of
magnitude larger than the intrinsic bandwidth. An example for the
systematic part is by the detuning by the radiation pressure forces or
Lorentz force detuning, which may be as large as 360 Hz for a gradient
of 20 MV/m. While this is of great concern for pulsed cavities, it can
be easily corrected in the CW application where the field is continuous.

More serious are the random tuning deviations. The random tuning
perturbations fall in two categories:

A.  [Relatively slow perturbations]{.underline}, with periodic intervals
    in the minute range. Random variations of the helium pressure
    represent a common cause.

B.  [Fast perturbations]{.underline} due to microphonics in the acoustic
    frequency range, caused by local mechanical stimuli (pumps,
    turbulence in the helium flow etc). The response is shaped by
    structural resonances and directional sensitivities of the cavities.

Slow mechanical tuners may be used to eliminate the slow perturbations.
Faster feedback systems are required to control the effects of
microphonics, which may extend their influence to approximately ± 25 Hz
from the RF frequency. To control against such rapid tuning variations,
the RF system must provide sufficient generator power to establish the
nominal field in the cavity under worst-case conditions of full detuning
by microphonics. The RF power requirement P~g~ can be expressed
analytically by:

![](media/image4.wmf){width="3.5694444444444446in"
height="0.4166666666666667in"}

where P~c~ is the cavity wall dissipation, b is the ratio beam
power/cavity wall power, ~B~ is the beam stable phase from crest, ß is
the cavity coupling factor, and ∆f is the cavity detuning (determined by
the microphonics spectrum).

In addition, the impact of beam loading from a 1 nC charge at 10 kHz
needs to be investigated. Such a bunch would shock-excite the cavities
and introduce transient behavior of the RF fields that must be corrected
by feedback systems.

Although phase control of 0.1° will be demonstrated elsewhere, the SMTF
will provide a test bed for the more demanding requirement of 0.01°
stability required for some applications. Thus, the requirement to
maintain field in the cavities under the influence of microphonics and
beam loading at modest (\~ 10 kHz) bunch rates has strong impact on the
cavity RF feedback system and RF power requirements, and thus costs.
Techniques to minimize detuning from microphonics may have significant
impact in CW SCRF systems design.

6.5 Power couplers

Superconducting RF systems require very little power to generate large
accelerating gradients -- for example the TESLA cavities may develop 20
MV/m with only 40 W input power under ideal conditions. In order to
accommodate for tuning variations as discussed above, however,
significantly larger RF drive power is required at the lower external Q,
typically 10-15 kW per cavity for Qext ≈ 107.

Power couplers must transport this power from warm waveguide or coaxial
supply lines, through intermediate temperatures, thermally isolating
sections, vacuum windows, to liquid helium temperature components, and
have mechanically adjustable components, while avoiding multipacting and
excessive heating.

## 6.6 Infrastructure requirements for a CW SCRF test facility

The SMTF should provide capability for measurements of CW SCRF
cryomodules, with the installation of RF power, cryogenic fluids and
transport, and test beams of electrons.

The CW tests will require, for each cavity, a klystron (or IOT) with
approximately 15 KW of power to establish 20 MV/m operating field with
control margin for dealing with microphonics at the optimum external Q
value, estimated to be about 2x10^7^. A high voltage power supply and a
small amplifier are needed to supply the klystron. We envision testing
cryomodules initially with two cavities per cryomodule.

The cryogenics plant for cavities operating at cw at 20 MV/m with Q of
1x1010 would be 60 W/m at 2 K allowing for a safety factor of 1.5.
Assuming advances in technology would triple the obtainable Q value, the
cw cryomodule refrigerator would be sized for 20 W/m at 1.8 K and about
5 W/m at 4.5 K. However, to ensure capabilities in early design stages,
where the higher Qo values may not be initially obtained, the cryogenics
plant should be designed with capacity of 120 W at 2 K, allowing two
cavities to operate with a 50% design margin on cooling capacity.
Additional pumping will be provided to allow operation at 1.8 K.Electron
beam availability is highly desirable for measurement of cavity
performance under transient effects induced by bunches of 1 nC at a
repetition rate of approximately 10 kHz. Cavity voltage and phase, and
wakefields in the complicated electrodynamics environment of cavities
assembled in a cryomodule would be essential in gaining confidence for
employing CW SCRF in demanding light-source applications. Bunch lengths
of 1 -- 10 ps, and transverse emittance of order mm-mrad would be
required.

\< 1, Pulsed Power Test Facility and Program for the Proton Driver

The Proton Driver is an 8 GeV proton linac. The last 85% of the linac (1
GeV to 8 GeV) is comprised of beta=1 TESLA modules and will benefit from
the ILC program. The synergy between ILC R&D and Proton Driver is
further reinforced by the almost complete overlap of an ILC module test
bed (Steps 1&2) and what will be needed for many aspects of Proton
Driver R&D. The proton driver will need 288 TESLA cavities in 36
cryomodules, as well as 96 low beta elliptical cavities in 12
cryomodules, all at 1.3 GHz. Two main uses are foreseen for the \< 1
test area: pulsed-mode front end linac for the Proton Driver, and a
possible production test facility for RIA cavities and cryomodules.

The initial RF systems will support pulsed mode operation at 325 MHz
(one quarter of the ILC's 1300 MHz) and extend the TESLA-style RF fan
out from one large Klystron to a large number of cavities. This will
support development of a family of "ILC-compatible" \<1 superconducting
cavities to be developed by members of the SMTF collaboration. These
include single, double, and potentially triple spoke SCRF cavity
resonators. At higher beta, the Proton Driver will also use cryomodules
with 1300 MHz elliptical cavities that will be tested in the 1300 MHz
test area.

![](media/image5.wmf){width="6.163194444444445in"
height="4.024305555555555in"}

Fig. 3 - Beta \<1 test area. The entire front-end linac is driven by a
single 325 MHz klystron. Although the single klystron should be capable
of driving the entire front end linac up to energy of \~100 MeV, the
beam energy will be limited to \~30 MeV by the length of beam line
enclosure available.

**Beam Tests.** A second phase of operation would add an H- source, and
RFQ, and Medium Energy Beam Transport (MEBT) operating from the same
pulsed Klystron that operates the SCRF cryomodules. This would provide a
beam-based test bed for LLRF and resonance control when driving low-beta
ion beams with multiple cavities driven from a single Klystron.
Emittance measurements, chopping, and laser stripping experiments will
be possible.

![](media/image6.wmf){width="6.127083333333333in"
height="4.550694444444445in"}

Fig. 4 -- Evolution of technology to be tested in SMTF beta\< 1 linac.
The beta\<1 test area would support a 325 MHz front end linac pattered
on the JHF/JPARC front end, then use SCRF spoke resonators patterned on
the RIA cavities. The 1300 MHz test area would support beta\<1
elliptical cavities and cryomodules, as well as beta=1 section patterned
on the ILC main linac.

A key new technology is the demonstration of fast high-power phase
shifters for SCRF resonance control of individual cavities while driving
a large number of cavities from a single large Klystron.

7.1 325 MHz Pulsed RF Systems for \<1 Test Area

A single 3MW Klystron (the Toshiba E740A currently in production for
JPARC) will provide pulsed RF power for the 325 MHz beta\<1 linac. See
fig.5.

The RF systems would be designed to support both the initial and upgrade
beam pulse parameters for the Proton Driver. Initial operation would
support beam pulses of (8.3 mA x 3 msec x 2.5 Hz), with an upgrade
scenario requiring (25 mA x 1 msec x 10 Hz). Two modulators are
currently under construction which can be reconfigured to support either
of these pulse parameters.

![](media/image7.wmf){width="5.740972222222222in" height="4.04375in"}

Fig. 5 - The RF distribution system for the 325 MHz beta\<1 pulsed SCRF
linac. In a TESLA-like scheme, directional couplers are used to split
off power for each cavity from a long waveguide running parallel to the
linac. Individual resonance control for each cavity is provided by fast
tuners using magnetically biased YIG ferrite to provide individual phase
and amplitude control for each cavity.

7.2 Program sequence for the 325 MHz Pulsed Linac \<1 Test Area

1)  Modulator construction (already underway).

2)  Order the 325 MHz Klystron, for delivery in FY05.

3)  In parallel, construct and begin cold tests of the RF fan out
    waveguide and directional coupler, to understand cross talk between
    couplers and related issues.

4)  Continue development of the fast-ferrite tuner modules, with the
    goal of having functional prototypes at each required power level by
    the end of FY05.

5)  Begin prototyping of 325 MHz cavities in various beta ranges by
    members of the SMTF collaboration.

6)  Funds permitting, begin procurement of the H-/RFQ front end.

7)  Continued development and simulation of LLRF hardware and control
    algorithms using the ferrite tuners.

8)  Integrated system test of the front-end linac, 325 MHz Klystron, RF
    distribution, ferrite tuners and LLRF control.

8\. \<1, CW Fabrication and Test Facility for RIA

The U.S. Rare Isotope Accelerator Project (RIA) will include the
construction of nearly 500 superconducting cavities of as many as 10
different types to accelerate ions over a velocity range 0.02 \< β \<
0.85. These cavity types will include TEM-class cavities such as those
shown in Figure 6. RIA will require facilities to clean and test the
individual cavities and also facilities to clean, assemble, and test
cavity strings and cryomodules. These facilities need not be at the RIA
site, and could in principle be included in SMTF. This said, however,
proximity to the RIA site would be useful in simplifying transport and
storage issues.

![](media/image8.jpeg){width="3.1493055555555554in"
height="2.6305555555555555in"}

Recent development of TEM-class, drift-tube cavities for RIA has
achieved new levels of performance by adapting ultra-clean surface
preparation techniques originally developed for TESLA velocity-of-light
structures to TEM cavities. This convergence of SRF technology of
low-velocity structures with that of high-velocity structures opens a
possibility of a processing and test facility being able to serve the
needs of both communities.

If SMTF can in fact be structured to accommodate such a broad range of
cavity types, it would be a unique facility in bringing together under
one roof the practitioners of several different types of SRF technology.
The opportunity thus afforded for discussion and sharing of technical
problems and solutions on a daily, nuts and bolts level amongst groups
with different experience and perspective could create a fertile and
creative environment for SRF development.

Within the RIA project there will be several classes of task that could
possibly be accommodated at SMTF:

1)  Cleaning and cold-testing of individual cavities, after chemical
    processing

2)  Clean assembly of cavities into cavity strings, forming a sealed
    assembly including RF couplers, beam line valves, and vacuum
    manifold and valves.

3)  Assembly of cryomodules incorporating the cavity strings.

4)  Cold test of assembled cryomodules.

A number of resources will be required to perform the above tasks at
SMTF. Some are similar to those required for other groups of users, such
as clean areas with provision for ultrasonic cleaning and high pressure
rinsing with ultra-pure water and clean storage for cavities and
associated components.
![](media/image9.jpeg){width="5.873611111111111in"
height="1.9201388888888888in"}

Because RIA uses low-frequency cavities which can operate at higher
temperatures than velocity of light structures, 4 K refrigeration at the
level of a few hundred watts will be needed for both single-cavity and
cryomodule cold-test capability. For single-cavity tests the ability to
operate at 2 K is needed, and also possibly for cryomodule tests with
805 MHz elliptical-cell cavities.

CW RF power at the level of a kilowatt will be required at several
different frequencies to test the different types of cavities required.
A single-cavity test cryostat can be designed to test most if not all of
the different cavity types and frequencies, but several RF sources will
be required for one of the configurations of the RIA driver being
considered, RF power at 57, 115, 172, and 345 MHz would be needed

The facilities required for RIA overlap to some extent with those
required for the front end of the proposed FNAL proton driver, which
will also require TEM-class cavities operating at 4.2K. The principal
difference is that for the proton driver the cavities will be operated
in a pulsed mode rather than cw, but the cavity types, cryomodules,
couplers, and tuners are likely to be similar in design.

Table 1 shows the resources that will be needed for various tasks during
the construction of RIA, which is expected to extend over a two to three
year period. Some of these facilities would also be useful for the
proton-driver, if schedules do not conflict.

9\. M&S Funds and Labor

The details of the funds required for the SMTF will be presented at the
time of the proposal.

10\. Summary

A group of laboratories and universities, working with US industrial
partners, is planning to construct a Superconducting Module & Test
Facility at Fermilab. The facility would be used for testing and
validating designs for both pulsed and CW systems. The facility would
bring together the expertise in cryogenic accelerators in the US and
help form the accelerator team that would help design the main linac for
the ILC. The SMTF will also fabricate several complete cryomodules in
collaboration with US industry, laboratories and universities. With this
expression of interest, we are informing the laboratory of this activity
and we are looking for direction on how you would like to receive such a
proposal.

Appendix I

# 11. Electron beam: Fermilab/NICADD photo injector laboratory

11.1 Introduction

Since 1992, Fermilab has been engaged in the production of
high-brightness electron beam. In conjunction with the TESLA
collaboration, it has constructed and operated an L-band (1.3 GHz) photo
injector, a copy of which was installed at the TESLA test facility in
DESY Hamburg, for various tests, especially for the proof-of-principle
UV SASE free-electron laser experiment. The Fermilab/NICADD photo
injector laboratory (FNPL) is used as a test facility for beam dynamics
studies associated to high brightness beam and its associated diagnosis,
along with application to advanced accelerator physics.

11.2 Facility and existing capabilities

![](media/image10.png){width="6.210416666666666in"
height="1.804861111111111in"}FNPL consists of a 1+1/2 cell L-band RF-gun
equipped with a high quantum efficiency Cesium-Telluride photo-cathode
allowing the photo-emission of electron bunches with charge up to \~20
nC). The generated bunches are further accelerated, up to 16 MeV, by a
downstream superconducting TESLA cavity operating with a nominal
accelerating gradient of \~12 MV/m (see Fig.1). Downstream of the cavity
the beam line includes a set of quadrupoles and steering dipoles
elements for beam focusing and orbit correction, a skew quadrupole
channel that allows the generation of flat beam using an incoming
angular-momentum dominated beam, and a magnetic bunch compressor chicane
which can enhance the bunch peak current up to approximately 2.5 kA. The
diagnostics for measuring transverse beam properties consist of
electromagnetic beam position monitors, optical transition radiation (or
YaG) screens (for measuring beam transverse density) and three emittance
measurements station based on the multi-slit mask technique. The bunch
length measurement is performed by a streak camera that streaks optical
transition radiation pulses emitted by the bunch. An alternative
frequency-domain bunch length diagnostics based on Martin-Puplett
interferometry of coherent transition radiation is also available.
Downstream of the beamline, the beam can be bent in a dispersive
section, to measure the beam energy distribution, or transported in a
straight ahead user experimental area. The FNPL facility can be operated
remotely. So far teams from LBNL, and DESY have used this capability to
remotely perform beam physics experiments.

*Figure 1: Overview of the FNPL facility in its present configuration.*

11.3 Current activities

Several beam dynamics and beam diagnostics activities are being actively
pursued at the FNPL photoinjector. Our main current efforts are (1)
photoinjector production of flat beam with emittance high emittance
ratio (goal \> 100), (2) longitudinal beam dynamics studies using a two
macro-particle bunch, (3) study of emittance control versus shape of the
photo-cathode drive-laser, and (4) emittance evolution of highly charge
electron bunches (15 nC). All these experimental studies also involve
theoretical and numerical modeling.

Collaborators from NIU and UCLA have been performing experiment on
plasma-wakefield acceleration. The experiment consists of injecting a
high charge (typically 10 nC) short (typically 3 ps) electron bunch in
Argon plasma. The experiment has both concentrated on demonstrating beam
plasma deceleration and acceleration. Recently the amplitude of the
plasma wake-field has been measured to be 130 MV/m. A refinement of this
experiment based on a drive/witness bunch set-up has been commissioned
by splitting the cathode drive-laser pulse into two pulses whose
transverse size and charge can be independently controlled.

Recently our UCLA collaborators have installed an experiment devoted to
realize an electron source based on the so-called plasma-density
transition. The experiment is now in its commissioning phase.

A team from the University of Rochester has developed a laser
functioning on the TM01\* mode, a mode with a longitudinal electric
field component. The laser is now ready and we plan, after the foreseen
energy upgrade of FNPL (see next section), to "couple" the laser and
electron beams with an open iris structure. At energies above 40 MeV, we
will be able to observed laser-based acceleration.

11.4 Upgrade Plans

The TESLA collaboration has recently offered to provide a second TESLA
cavity that has been tested to achieve accelerating gradient up to
approximately 35 MV/m. We plan to install this second cavity downstream
of the first one to boost the beam energy to approximately 45 MeV. Such
an energy increase (by a factor \~3 compared to the present setup) will
considerably reduce the impact of space-charge forces on the beam
dynamics and thereby resulting in a better control of transverse
envelope and emittance. The FNPL upgrade will also allow the support of
various "user experiment" like, for instance, the laser acceleration
experiment (using the laser developed by University of Rochester).

In the process of this beamline extension we also configure the beam
line to allocate room for two 3.9 GHz superconducting cavities being
developed at FNAL: a deflecting and an accelerating mode cavity. The
deflecting mode cavity was developed in the context of the Kaon
separation out of the secondary beam produced at the main injector at
FNAL (so-called CKM experiment). It has also applications in the LUX
proposal at LBNL to generate ultra-short X-ray pulses. The deflecting
mode cavity was developed to linearize the longitudinal phase space and
thereby enhance the peak current of accelerator working on the 1.3 Ghz
frequency. Such a "linearizer" has applications in the context of light
source (TESLA VUV/X-ray FELs, LUX project at LBNL, etc...) and also
linear collider (TESLA post damping ring bunch

![](media/image11.png){width="5.517361111111111in"
height="1.8944444444444444in"}*Figure 2: Overview of the upgraded FNPL
facility. The facility will incorporate two TESLA cavities, one
accelerating and one dipole mode 3.9 Ghz cavities.*

compressor). At FNPL the use of these two cavities simultaneously will
provide a direct measurement and optimization tool of the longitudinal
phase space linearization concept. The deflecting cavity alone also
provides a unique diagnostics that should allow the measurement of beam
parameters within the bunch (so-called slice parameters) and provide a
refinement in understanding the beam dynamics of space-charge-dominated
electron beams. A schematic of the proposed FNPL upgrade is shown in
Figure 2.

11.5 FNPL upgrade as an e- injector for SMTF

In the context of SMTF, the upgraded version of FNPL would provide an
ideal injector that could, at a later stage, be transplanted on the SMTF
site. A configuration consisting of an RF gun followed by the two TESLA
cavities, as planned to be operated at FNPL, would provide a transverse
emittance-compensated beam. According to preliminary numerical studies,
such a beam could then be subsequently accelerated by a TESLA
accelerating module operated at any accelerating gradient without
significantly impacting the transverse emittance (see example in Figure
3). Such a feature means that an injector consisting of an rf-gun with
two TESLA cavities only (in the present case operated at 12.5 and 25
MV/m average accelerating gradient) would be an independent entity that
could provide controllable beam parameters to be injected in SMTF. The
current FNPL facility (one RF-gun followed by one TESLA cavity) does not
provide such a capability: the beam is still strongly
emittance-dominated: even over a short drift the beam parameters tend to
degrade. Therefore FNPL upgrade, while enabling the extension of the
current advanced accelerator physics program, could also be viewed as
the first phase of SMTF. Parametric studies and subsequent optimization
of the system should allow the production of high quality beam with the
nominal linear collider charge such a beam could then be injected. The
FNPL upgrade will also provide operational experience and training for
future scientist working at SMTF. We anticipate the upgrade of FNPL (to
be ready for SMTF) to include: the installation of the TESLA cavity
offered by DESY, an upgrade of the photocathode drive-laser (to improve
the reliability of the facility) and at a later stage the installation
of the two 3.9 GHz cavities. In parallel we advise the development and
construction of a new symmetric RF-gun cavity such as the one in
operation at the TTF-2 FEL facility.

![](media/image12.jpeg){width="5.530555555555556in"
height="4.124305555555556in"}*Figure 3: Example of transverse emittance
(black) and kinetic energy (red) evolution for a 3.2 nC bunch (TESLA
nominal charge). C1 and C2 are the two TESLA cavities to be operated in
the FNPL upgrade (here operated at 12.5 and 25 MV/m average accelerating
gradient). The upgraded FNPL injector extend from z=0 to z=8 m. The beam
is then injected in a TESLA accelerating module. The magenta curves
stands for the longitudinal fields, i.e. the location of the TESLA
cavities.*

Appendix II

For more information on Cryogenic for SMTF at Fermilab please see URL.
This file is not attached due to its size.

<http://ilc-dms.fnal.gov:1352/Members/mishra/cryogenics.pdf>

Appendix III

For more information on cavity and cryomodule fabrication and testing
and supporting infrastructure please see URL. This file is not attached
due to its size.

<http://ilc-dms.fnal.gov:1352/Members/mishra/Cavity_fabrication.pdf>

[^1]: Transplant the A0 photo injector (A0PI)

[^2]: We expect availability of TTF will be limited due to its
    transformation into a FEL user facility

[^3]: The vertical Dewar is actually a Fermilab design (Fermilab's
    contribution to TESLA).