BEAM PROPERTY MANAGEMENT AT KEK ELECTRON / POSITRON
7-GeV INJECTOR LINAC
K. Furukawa∗ , N. Iida, T. Kamitani, S. Kazama, T. Miura, F. Miyahara, Y. Ohnishi, M. Satoh,T. Suwada, K. Yokoyama, KEK, 1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan
High current gun,
10 nC for e+	Abstract

BJ-arc
1.5 GeV

emittance RF-gun
A Low
5 nC for e–

1.1 GeV
e+ damping ringPF

50 Hz (e+ or e-)
Pulse-to-pulse
modulation	

2.5 GeV
0.2nC x 1

IrCe cathode, Fiberlaser, QTWSC cavityThe electron / positron injector linac at KEK has injecteda variety of beams into the electron accelerator complex ofan asymmetric collider and light sources for particle physics
and photon science experiments for more than 30 years. The
beam property of electrons and positrons varies in energy
from 2.5 GeV to 7 GeV and in bunch charge from 0.2 nC to 10nC, and their beam emittance and stability requirements arechallenging dependent on the injected storage rings. They
have to be switched by pulse-to-pulse modulation at 50 Hz.
The emittance control is especially crucial to achieve thegoal at SuperKEKB and is under development. The beamenergy management becomes more important as it affects allof the beam properties. Beam acceleration provided by 60
high-power microwave stations should be properly arranged
considering redundancy and stability. Thus, the equipment
controls are also restructured in order to enable the precise
control of the beam properties, based on the synchronized
event control system and EPICS control system. The strategy
and status of the upgrade is discussed from the practicalaspects of device controls, online simulation and operation.

beam and a flux concentrator for high-current positron capture are introduced. It is crucial for the injection operation
with higher stability and accuracy to achieve lateral equipment alignment less than 0.3 mm over 600 m linac, and lessthan 0.1 mm in a short segment. The designed beam should
be delivered with iterative corrections understanding thestatic and dynamic properties of the accelerator equipment
and evaluating the beam properties in every conceivableway.
These beam operation management processes need to beimproved for SuperKEKB on the basis of the techniquesachieved in KEKB.

INTRODUCTIONACCELERATOR EQUIPMENTAt High Energy Accelerator Research Organization(KEK), SuperKEKB, the electron-positron asymmetric collider, is under construction [1]. This project is expected tobe able to elucidate the flavor physics of elementary particles
with 40-fold improved luminosity compared with the initialKEKB, by doubling the stored beam current, and also by thenano-beam scheme to shrink the beam size down to a twentieth at the interaction point. SuperKEKB is composed of theelectron-positron injector, high-energy electron ring (HER),
low-energy positron ring (LER), and a positron damping
ring (DR).
The Electron-positron injector will perform the first injection to SuperKEKB in Japanese fiscal year 2015. It will
fill the dual rings of SuperKEKB as well as two light source
rings in top-up mode in 2017 with significantly different
beam properties while switching beams at 50 Hz as shownin Fig. 1. The beam energies are 2.5 GeV for Photon Factory (PF), 6.5 GeV for PF Advanced Ring (PF-AR), 4.0 GeV
positron for LER and 7.0 GeV electron for HER, respectively [2].
Especially, it is a major challenge to inject beams toSuperKEKB with a small emittance of 20 mm·mrad andan energy-spread of 0.1% under the large beam current of 5nC per bunch. In order to achieve such a high quality beam,
a new RF gun for high-current and low-emittance electron

The injector linac is operated with the EPICS control
framework at the lower and middle layer [3], the event-based
control system (MRF) at the lowest layer, and the script
languages including SADscript for online accelerator design. This combination was quite successful at the both
KEKB injector and collider rings, and is maintained forSuperKEKB as well, with many improvements such as embedded EPICS systems [4,5]. This environment is supportedby the carefully-managed control databases.
Example of static database of accelerator equipment for
beam-property management is shown in Fig. 2.

∗ kazuro.furukawa@kek.jp

Primary e– for e+
3.2 GeV, 10nC x 2
Bunch
Compression

CBunchCompression

e+
1 New
Capture2

SY2

EnergyCompression

EnergySY3 Compression

345with FC & LAS

LER

4.0 GeV e+
4nC x 2HERPF-AR

7.0 GeV
5nC x 220 um

6.5 GeV
5nC

Figure 1: Layout of injector linac and its beam delivery tomultiple experimental facilities.

Design/Construction of Accelerator/Equipment!

Geometry!
(eqtbl)!

Microwave!
(kly*tbl)!

Beam monitor!
(sp*tbl)!

Basis ofbeam optics!

Beam accel.!
Beam manip.!

Beaminstrumentations!

!

!

!

Magnet & P.S.!
(mg*tbl)!

Acc. structure!
(acrftbl)!
Beam accel.!

Beam manip.!
!

Accelerator Operation and Beam Controls!

Figure 2: Construction of static database and its contribution
to linac beam operation.

Geometrical arrangement
Each device comes with a name that is up to six characters, the two-character device type name, a sector namethat represents the installation location (A, B, R, C, 1, 2,3, 4, 5, 6, etc.), an unit number (1-8, etc.), an accelerating
structure or magnet number (0-6), and a sequence number.
Each equipment database is a table that has the device nameas the key.
As basic information, the equipment database (eqtbl) contains the group name of each device, the distance from theelectron gun, the mechanical length, the effective length,and so on. Presently, such geometrical information and theCAD drawings are not automatically reflected each other. Acertain mechanism to directly exchange information is being
developed.

Accelerator devices
For the beam transport, the magnet and its power supply
information, conversion factors to/from control value, electric current and magnetic field as well as optics correction
factors based on beam measurement are maintained in several databases (mgtbl, mgbtbl, mgbftbl). The convention
how to define those factors varies between facility to facility,
and reasonable one was redefined for the KEKB project, andutilized so far to manage the beam optics.
For beam acceleration, the microwave modulation information (klytbl) and beam acceleration gain information(acrftbl) are prepared and refined using beam measurement,
and it is employed to calculate the beam energy and otherbeam properties along the linac.
There are many other databases for accelerator equipment,
beam instrumentations, vacuum system, utilities, and so on.
The database for beam instrumentation such as beam position
monitors (sp*tbl) has a large number of parameters per adevice.

CONFIGURATION OF THE INJECTOR
The injector in SuperKEKB project as in Fig. 1 has eightsectors (A∼C, 1∼5) of 80-m length each with the exceptionof the sector A of about 40 m. Each sector has typicallyeight 10-m long accelerating units, with a high-power RF
modulator and four 2-m long accelerating structure (cavity).
Entire 600-m injector is divided into four sections fromthe viewpoint of beam operation. In each section, one or twounits are designed to be redundant for a margin in energy
gain. At the end of each section an energy knob is assigned toa pair of units to define the beam energy. Energy knobs andmany other units are equipped with fast RF phase shifters, toenable the energy change at 50 Hz through the event control
mechanism [6]. Each unit in an energy knob shifts RF phaseto the opposite direction to suppress the energy spread asshown in Fig. 3.

Figure 3: Energy knob to adjust beam energy from crest
phases (green) to operation phases (red) compensating energy spread.

BEAM ENERGY MANAGEMENT
It is necessary to manage the beam energy at each injector
location by estimating the energy gain at each unit, in orderto enable the beam optics calculation.

Adjustment of the microwave source
At first, RF conditions for the maximum energy gain ateach unit would be stored into EPICS online database. While
there is a method to determine the proper RF phase measuring the beam-induced field, the precision is not enough under
our circumstances. Therefore, the beam position measurement at large dispersion function is employed to determine
the crest RF phase as well as pulse timing for the maximum
acceleration.
Based on the above condition, it is necessary to shift theRF phase off the crest in order to suppress the energy spread
due to the longitudinal wake field depending on the beam
current. Furthermore, the pulse timing should be adjusted
at the both shoulders of the RF pulse in order to accelerate
two bunches in a pulse 96-ns apart with the same energy.

Determination of the beam energy
By using the RF and acceleration database, the correctedenergy gain at each unit is calculated and the accumulated
energy is stored into the online database. In order to increase
the overall reliability, the energy gains are regulated and optimized every week observing the high-voltage discharge rate,
the field emission condition, the stability of the power supply,and so on. Otherwise, the related interlocks for equipment
protection may disturb the beam injection. This process isimportant since the beam energy at each location directly
affects the accuracy of the beam optics calculation [7].

Energy stabilization
Depending on the injected ring among HER, LER, PF andPF-AR, the compensating off-crest phases and longitudinal
wakefield as well as the beam energies are different because
the beam currents are different. Thus, the operating points ofenergy knobs to secure the energy are also different. Therefore, it turns out that a single injector linac behaves as one offour separate virtual accelerators that are switched one another every 20 ms by the event control mechanism. Actually,operating points of more than 200 devices are changed between those virtual accelerators, and each virtual accelerator
must be treated in different manner [5].

Event-basedControl System	
Every
20 msF.B	
F.B	

e– GunARC

PF Injection	

e– (2.5GeV, 0.2nC)

F.B	
e– GunARCe–Damping ring

SuperKEKB-LER Injection	

F.B	

(3.5GeV, 10nC)

F.B	

e+ Targete+ (4GeV, 4nC)

e– GunARC

SuperKEKB-HER Injection	

F.B	

e– (7GeV, 5nC)
e– GunARC

F.B	

PF-AR Injection	

F.B	

Figure 5: Controlled recoveries (blue) of blew-up emittances(red) with adjusted initial beam positions and angles for 100
random initial simulation orbits.

e– (6.5GeV, 5nC)

Figure 4: Each virtual accelerator (VA) would be associatedwith several beam feedback loops, independent of loops inother VAs.

For the end of each section of those virtual accelerators,independent energy stabilizing feedback loops need to beinstalled as shown in Fig. 4. Similarly, the energy equalizing
feedback loops for two bunches within a pulse are requiredby adjusting the pulse timings. These will be operated withenergy knobs and timing adjustments by the beam position
measurements at locations of large dispersion functions [8].

BEAM ORBIT AND EMITTANCEMANAGEMENT
During KEKB operation, a large number of orbit stabilization feedback loops were required because of poor air
conditioning stability and alignment accuracy, and an attention was paid to maintain the beam orbit not to loose thebeam [9].
Towards SuperKEKB, it is necessary to have more accurate orbit controls in order to suppress emittance blow-up.
According to a simulation, including the random alignment
errors of the accelerating structures and the quad magnets,
the beam may have 100-times large emittance easily. The
simulation suggests it is possible to deliver a required beam
only if their alignment is less than 0.3 mm (rms) for overall 600-m injector and 0.1 mm (rms) for a short segment
as shown in Fig. 5. In the method the choice of an orbit
can cancel the longitudinal bunch deformation. To that end,
the angular accuracy of the steering coil needs to be lessthan 1 µrad [10, 11]. The beam position read-out system ofprecision less than 10 µm is also developed to support themethod [12, 13].
If it is possible to maintain the orbit, the emittance canbe preserved. For example, several orbit stabilization feedback loops may be installed so as to fix the beam angle
and position at several locations along the injector. ForSuperKEKB multiple feedback loops are necessary with respect to the both HER and LER injection virtual accelerators
independently. In order to operate the mechanism flexibly
and reliably it is required to refine the quality of the machine
database and to maintain the advanced beam optics model.
However, as it has been found in the measurement of longterm floor joint movement that each part of the building move
up to a millimeter yearly. More precise and continuous measurements will be performed and absorption or correction
mechanism including a mover girder will be installed in order to cure the issue. We need to design the corresponding
operational software for emittance preservation.
In addition, not only the transverse beam emittance, butalso the beam energy spread or longitudinal beam emittance should be controlled by bunch shape measurementin accordance with integrity of beam generation and bunch
compression [14].

DATABASE IMPLEMENTATION
Presently, each control database is configured as a text
file of a table in a predetermined format, in which each row
corresponds to a device name as a key, and each column represents a device property. Further comments can be written
at any row, such as the device history.
Procedures to deal with databases are available in several
programming languages. For C/C++ language the databaseis converted into a hash database in memory, and it canbe utilized efficiently [15]. For scripting languages it isconverted into a associative array. Also, a set of programs isprepared for the database integrity check and management.
Because a database management system (PostgreSQL) is
already used for multiple purposes in the operation, it seems
to be natural to manage those accelerator property databasesin PostgreSQL, and it is implemented as a test for the nextphase of the beam commissioning. At the same time, moreand more database elements are put into the EPICS database,and conversion procedures are prepared.

On performing beam optics calculation, a part of the information is taken from database and other information is
directly taken from EPICS online process variables throughthe channel access protocol. For such purposes, SAD / SADscript environment for the beam control is quite flexible andis used extensively [16, 17]. Many of such operation programs are designed to refine databases scanning device andbeam parameters.

CONCLUSION AND FUTURE
The management of beam properties in the KEK electron
positron injector linac was considered based on the controls
and databases. Especially for the realization of SuperKEKB,
a reliable operation management is required for advanced
beam quality and complex virtual accelerators (beam operation modes) with robust databases, calibrations based onbeam measurements, iterative refinements of beam optics
model in each virtual accelerators, and preservation of finebeam emittance and energy. Based on the experiences in
KEKB project the controls and management of beam properties should be further improved during SuperKEKB beamcommissioning phases.

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