The KEKB Injector Linac
I. Abe, N. Akasaka, 1 M. Akemoto, S. Anami, A. Enomoto,J. Flanagan, S. Fukuda, H. Fukuma, Y. Funakoshi,
K. Furukawa, H. Hanaki, 1 H. Honma, N. Iida, M. Ikeda,
K. Kakihara, N. Kamikubota, T. Kamitani, H. Katagiri,
T. Kawamoto, M. Kikuchi, H. Kobayashi, H. Koiso,
T. Matsumoto, S. Michizono, K. Nakahara, 1 H. Nakajima,
K. Nakao, Y. Ogawa, Y. Ohnishi, S. Ohsawa, K. Oide,
T. Oogoe, Y. Otake, 1 I. Sato, 1 K. Satoh, T. Shidara,
A. Shirakawa, M. Suetake, T. Suwada, T. Urano, 1
S. Yamaguchi, Y. YanoHigh Energy Accelerator Research Organization (KEK)
1-1 Oho, Tsukuba-shi, Ibaraki-ken, 305-0801, Japan

Abstract
An 8-GeV electron/3.5-GeV positron injector for KEKB was completed in 1998
by upgrading the existing 2.5-GeV electron/positron linac. The main goals were
to upgrade its accelerating energy from 2.5 to 8 GeV and to increase the positron
intensity by about twenty times. This article describes not only the composition andfeatures of the upgraded linac, but also how these goals were achieved, by focusing
on an optics design and commissioning issues concerning especially high-intensity
single-bunch acceleration to produce positron beams.
Key words: electron, positron, injector, linac

1

Introduction

An electron/positron injector linac at KEK, capable of providing electrons at
an energy up to 8 GeV and positrons up to 3.5 GeV, is used as a multi-purpose
injector not only for the KEK B Factory (KEKB), but also for the Photon
1

Presently left from KEK.

Preprint submitted to Elsevier Science

5 March 2002

Factory (PF). At present, it delivers full-energy beams of 8-GeV electrons
to the KEKB High-Energy Ring (HER) and 3.5-GeV positrons to the LowEnergy Ring (LER) using the entire linac. Further, beams of 2.5-GeV electrons
are provided for the PF two light sources (the PF and the PF-AR) using a
gun installed halfway of the linac.
The linac was originally constructed as a 2.5-GeV injector for the PF in 1982
[1–3]; a positron source was later added for the TRISTAN electron/positron
collider [4]. However, this old linac was extensively reconstructed for the BFactory project during 1994-1998 [5]. The two essential goal of this upgradewere to achieve an electron beam energy of 8 GeV and a single-bunch positron
intensity of 0.6 nC. The former goal has been accomplished by increasing boththe linac length (from 400 to 600 m) and the acceleration ﬁeld strength (from8 to 20 MV/m), and the latter by increasing the primary electron energy (from
250 to 3.7 GeV) with high-intensity electron beams (10 nC/bunch).
The linac is shaped like a “J” as shown in Fig. 1, because the land was notenough to extend the linac straight. Two linacs are linked by a 180-degree
bending beam transport (called J-arc). The whole linac consists of 55 S-band(2856 MHz) main accelerator modules, with a pre-injector (#A-1), a positron
capture module (#2-1), and a module for energy-compression system (ECS)
for positron beams. Seventeen upstream modules were newly constructed for
KEKB. Each of the main accelerator module provides an average energy gainof 160 MeV.
The linac presently serves four rings by switching the beam modes. In thepositron-beam mode, a radiator is inserted into the beamline at the half pointof the linac. A large number of parameters, such as in the magnets and rf
phases, are automatically switched from one mode to the other.
Since December, 1998, when KEKB commissioning started, injection fromthe linac has been successfully performed [6]. By sharing the injection timefor KEKB and the PF/AR without interference and saving injection time,
the linac has greatly contributed to the integrated luminosity in B-physics
experiments. Table 1 gives the main design beam parameters and the results
achieved so far.

2

Beam optics and dynamics

Several issues concerning beam optics and dynamics in realizing a high-intensity,
single-bunched, primary electron beam for positron production as well as in
the beam transport of a secondary positron beam and an 8-GeV, low-intensity
electron beam are discussed in this section. Special emphasis is laid on the2

PF

KEKB / AR

Beam Switchyard
ECS
5-8
5-7

N

5-6
5-5
5-4

W

Sector 5

5-3

E

5-2
5-1

S

4-8
4-7

(13.5 deg)

4-6
4-5

Sector 4

4-3
4-2
4-1
3-8
3-7
3-6
3-5
3-4

Sector 3

3-3
3-2
3-1

483 m
2-8
2-7
2-6
2-4

Sector 2

2-3
2-2
2-1/1-8

Electron Source

Positron Source
1-7(Gun_KEKB)

1-6

Buncher

1-5

Sector 1
A-1
A-2

Sector A

1-4
1-3
1-2

A-3

1-1

A-4

C-8

B-1

125 m

(Gun_RF/AR)

C-7

B-2
C-6
B-3

Sector B

C-5

B-4

Sector C

C-4

B-5

C-3

B-6

C-2
B-7
C-1
B-8

AssemblyHall

180-deg.
Bend(J-Arc)Fig. 1. Overall layout of the KEK electron/positron linac.

3

Table 1
Linac design beam parameters and performance.
8-GeV electron(1) Gun(2) Buncher

Goal

Achieved

Goal

Achieved

Energy

keV

200

200

200

200

Intensity

nC/pulse

1.5

2

13

14

Pulse width

ns

2

1.8

2

2.8

Energy

MeV

16

16

15

15

2

2

1.9

> 10

11

Energy spread (σ)

MeVIntensity

nC/pulse

1.4

mm

0.06

Eﬃciency
Emittance γβε (σ)(3) Arc

3.5-GeV positron

95%
0.04

90%
0.06

Bunch width (σ)

ps

2.1

2.5

6.7

4.2

Energy

GeV

1.5

1.7

1.5

1.7

Energy spread (σ)

MeV

0.6%

0.29%

0.6%

0.38%

Jitters (p-p)

0.1%

Drift (with feedback)Emittance γβε (σ)< 0.2%/hmm

0.17Transmission(4) e+ target

100%

EnergyGeVIntensity

nC/pulse

1.7
> 95%

100%

3.7

3.7

> 10

10

Transmission(5) e+ Solenoid exit

(6) Linac end

0.08

96%

Intensity

nC/pulse

2.4

Speciﬁc yielde+ /e− GeV

Energy

GeV

8

>8

3.5

> 3.5

Energy spread (σ)

MeV

0.15%

0.05%

0.125%

0.15%

Intensity

nC/pulse

1.28> 1.28> 0.64

Speciﬁc yielde+ /e− GeV

6.8%

0.82
2.3%

Transmission> 80%

Emittance γβε (σ)

mm

0.25

0.31

1.5

1.4

Pulse repetition

pps

50

50

50

50

space-charge and wake-ﬁeld eﬀects caused by a high-intensity beam in a bunching section and regular acceleration sections [7].
2.1Pre-injector

The main task concerning the pre-injector (Fig. 2) has been to accomplisha high-intensity, single-bunched beam with a proper beam characteristics: acharge of 10 nC, a bunch length of 4.2 ps (σ: the standard deviation for theGaussian-curve ﬁt) and a normalized emittance well below 0.1 mm (σ). The
design guidelines for realizing this were the following:• Increase the pulse voltage of the grid pulser for the electron gun [8] to4

Fig. 2. Proﬁle view of the pre-injector of the linac.

generate a high-intensity beam, while keeping the pulse length short enoughfor subsequent bunching sections (2 ns).
• Raise the acceleration voltage (200 kV) of the electron gun so that spacecharge forces can be suppressed as much as possible.
• Introduce a two-subharmonic-buncher system [9] (SHB1 at 114 MHz and
SHB2 at 571 MHz) immediately after the electron gun, allowing smoothpulse compression in the following bunching section. The principal reason
for not adopting a one-subharmonic-buncher system (e.g. SHB2) is that ahigh-intensity beam with a suﬃciently narrow pulse width of 0.6 ns, corresponding to about one third of the period of SHB2, can not be generated
by the usual grid pulser.
• Restrict the role of SHB1 to gathering all of the electrons from the gunaround an appropriate phase range of the next SHB2 by accommodatinga relatively modest modulation voltage (100 kV) and a corresponding drift
space for rather loose pulse compression.
• Raise the modulation voltage (140 kV) at SHB2 and minimize the subsequent drift space to achieve fast and tight pulse compression against thede-bunching eﬀects due to space-charge forces.
• Integrate the S-band (2856 MHz) prebuncher (PB) and buncher (B) [8]into a single unit to shorten the distance between them for evading any
de-bunching eﬀects, while optimizing the acceleration voltage both in PB
and B (1.3 MV/m and 20 MV/m, respectively).
• Optimize a solenoid-focusing ﬁeld in the pre-injector to keep the Brillouin
ﬂow for minimizing the emittance increase due to space-charge forces, especially while paying attention to the ﬁeld strength (maximum 0.2 T) in
the ﬁrst several cells at the buncher. Figure 3 shows simulation results by
PARMELA [10], indicating that the designed beam characteristics of a highintensity, single-bunched beam for positron production is obtained using theparameters listed in Table 2.

5

SHB2

SHB1

Buncher

PB

14
12

1500

10
8

1000

6
4

500

Energy [MeV]

Bunch Length [psec]

2000

2
0
0

0.5

1

1.5

2

2.5

3

0
3.5

Distance [m]Fig. 3. Simulation of the beam dynamics from a gun to a buncher exit (upper); thebeam phase space at the bunch exit (lower).
Table 2
Parameters of the principal components in the pre-injector.
Parameters

SHB1

SHB2

Pre-Buncher

BuncherAcc. Sec.

Frequency [MHz]

114

571

2856

2856

2856

Shunt Impedance [MΩ]

1.14

3.04

14.97†

54.50†

57.97†

Unloaded Q

6989

12580

10140

12000

13810

Power [MW]

0.011

0.007

1

23

12 x 2( † MΩ/m )2.2

Wake-ﬁeld issues

The primary concern for wake-ﬁeld issues was whether a high-intensity, singlebunched primary electron beam for positron production could be stably accelerated up to the positron production target without any degradation of thebeam quality due to wake-ﬁeld eﬀects, which might drastically decrease thepositron production yield. In this section, therefore, a discussion is made concerning the single-bunch wake ﬁeld. Longitudinal wake ﬁelds generated at thehead particles within a bunch could lead to a large energy spread, which, forinstance, might surpass the energy acceptance at the J-arc section. Transverse6

wake ﬁelds caused by an oﬀ-axis beam or misalignment of accelerator components might give rise to a head-tail instability, resulting in beam loss or a large
beam size on the positron production target. Assuming the parameters listed
in Table 3, the wake-ﬁeld eﬀects have been estimated in a primary electron
beam for positron production [7].
Table 3
Parameters for investigating the transverse and longitudinal wake ﬁelds.
Acceleration Frequency

2856 MHz

Charge (No. of Particles)

10 nC (6 ×1010 )Bunch Length (σ)

1.3 mm

Acceleration Field

20 MV/m

Total Acceleration Length

200 m

Initial Energy

100 MeV

Final Energy @ Positron Target

4 GeV

Betatron Wavelength

40 m

Beam Size @ Positron Target

0.6 mmTransverse Wake-Field Strength

3 ×1015 V/C/m2

The results are summarized as follows:• The optimum bunch length for a 10-nC beam concerning the energy spreadis 1.3 mm (σ). If the bunch length is shorter than this, longitudinal wakeﬁeld eﬀects become dominant, giving a larger energy spread compared with
the natural energy spread determined by the bunch length.
• An energy spread of 0.38% (σ) is attained for a 10-nC beam with this bunch
length if it is accelerated on an oﬀ-crest angle of about 10 degrees in theacceleration phase of microwaves. This is within the energy acceptance of
the J-arc section (0.6%).
• According to a numerical simulation for the transverse wake-ﬁeld eﬀects,
the initial oﬀset at the exit of the pre-injector for a 10-nC beam must be
much smaller than 0.5 mm, if the beam size on the positron production
target is to be 0.6 mm in radius for stable positron production. This could
be easily achieved by tuning the corresponding steering coils.
• The same calculation shows that the misalignment of the accelerator sections must be much smaller than 0.8 mm in setting tolerances for a 10-nC
beam, while the quadrupole magnets (quads) must be aligned with a precision much better than 0.12 mm. Although the tolerance for the quads might
be a rather tight constraint compared to the other, it should be realizablesince the best setting error of the present alignment system so far achieved
is around 0.05 mm.
• If the beam charge is larger than the design value of 10 nC, we will need7

some methods to cure any degradation of the beam quality due to both
longitudinal and transverse wake-ﬁeld eﬀects.

2.3

Beam transport and ECS (energy compression system)

The basic design concepts of the beam-transport system in the linac comprising the J-arc section and the ECS are summarized in the following:• The beam transport in regular accelerator sections is basically a periodic
system of quad-triplets, except for a periodic system of doublets or a FODO
system of singlets in some regions where severe constraints on installation
space exist.
• The criterion for the optics design is based on the requirements that the 3σ beam emittance, which adiabatically damps with acceleration, should besmaller than the acceptance of the focusing system. The initial normalized
emittance at the exit of the bunching section is assumed to be a calculated
value (60 µm (σ) by PARMELA), while the acceptance is maximized fora periodic system by choosing an appropriate betatron phase shift in one
period.
• Wake-ﬁeld eﬀects are taken into account for high-intensity, primary electron
beams for positron production by installing as many quads as possible along
the linac up to the positron production target to strengthen the focusing
force.
• In this connection, two diﬀerent optics are optimized for two modes corresponding to the KEKB electron beam and the positron beam, respectively.
• The J-arc section is designed to be achromatic and isochronous so as to accomplish the conservation of the transverse emittance and the bunch length,
assuring preservation of the beam quality [11]. Sextupole magnets are also
introduced for higher order corrections.
• The ECS comprising a chicane-magnet system and two accelerator sections
is introduced into the end of the linac for almost halving the large energy
spread of positron beams (σdesign = 0.25%), which is about twice as large
as that of the beam-transport line to the ring (σdesign = 0.13%).
Optics simulation results by TRANSPORT [12] are shown in Fig. 4, verifyingthat the calculated beam size is well below the physical aperture.

3

Main accelerator module

The basic composition of the main accelerator module involves four 2-meter
accelerator sections fed by one high-power klystron. The standard module8Fig. 4. Calculated beam proﬁles through the linac. 8-GeV electron beam proﬁlealong the entire length of the linac; (solid line) horizontal; (dashed line) vertical.
3.5-GeV positron beam proﬁles downstream from the positron production target;(solid line) horizontal, (dashed line) vertical.

FRONT VIEW

SIDE VIEWKLYSTRON GALLERY
MODULATOR
1779.5(3684.93)
2234.93190.5
541

MAGNET & VACUUM
POWER SUPPLYs

50-MW KLYSTRON SLED1970 (WG)(2278.75)

4800

2180

4680

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
2000(Hole)

700

1350

1755

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
1450

4513.68 (43x10.4969)

989.514 x 2-m SECTIONs(2436.32)

1000

2500

ACCELERATORTUNNEL

;;;;;
;;;;;
;;;;;
;;;;;
1200 ;;;;;;;;;;
150 ;;;;;
;;;;;

460.5
3000

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;
;;;;
;;;
;;;;
;;;
;;;;
;;;
;;;;
970
;;;
;;;;
1500

2500

2099.39

BEAM;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

1000

9600 (1-module length)

Fig. 5. Cross section of the linac main module.

length is 9.6 m. Each module has an energy gain of 160 MeV with a klystronpeak power of 41 MW and using a SLED-type rf pulse compressor. A total of 55
modules can therefore accelerate electrons to a maximum energy of 8.8 GeV.
These modules are installed in an underground accelerator tunnel, and areconnected to the rf source in the klystron gallery at the ground level. The
two rooms are separated by a 2.5 m thick concrete wall for radiation shielding(Fig. 5).
9

Fig. 6. Cross section of the 2-m section used in the main modules.

3.1

Accelerator structure

The accelerator section is an S-band (2856 MHz), 2 m long disk-loaded structure of the 2/3π mode. The structure was designed to produce a quasi-constantaxial electric ﬁeld by changing the disk-hole diameter (so-called 2a dimension)
stepwise by 75 µm from the entrance to the exit over the 2-m section. For dispersing the resonance frequency of beam-blowup modes, though this eﬀectconcerns the multi-bunch case, six types of structures were made with diﬀerent sets of 2a dimensions. The shunt impedance of the structures is from 57.3
to 58.3 MΩ/m and the ﬁlling time is 0.46 to 0.56 µs.
All of the structure were fabricated by an electroplating technique, which isused to form an integral, vacuum-tight structure by electroplating the outsideof an assembly made of disks and cylinders. The thickness of the electroplatingis 5 mm. An advantage of this method is to eliminate the need for tuning, because the electroplating is made in a room temperature and hardly distorts theprecisely machined dimensions. About eighty sections were newly fabricatedfor the extension of the linac [13].
Before the upgrading, using a resonant ring, one of the old accelerator sections
fabricated during 1980-1981 was tested to assure that it could operate atmore than 20 MV/m [14]. After having fabricated a new rf source, the newaccelerator section was conditioned for an accelerating ﬁeld of up to 40 MV/m
[15].
The operation temperature is 30 degrees C., which is maintained within 0.1
degrees so that the phase shift along the entire length of an accelerator section
is kept within 2 degrees.
The vacuum system for the old injector was used for the main modules, withimprovements in some locations such as rf windows separating klystrons fromaccelerators and the positron capture sections. The vacuum inside the regularaccelerator sections is estimated to be several 10−6 Pa by using a pressuredistribution analysis method [16].
10

3.2

Alignment of the module

As described in the previous section, the linac modules must be aligned along
the straight beamlines with a precision of better than 0.8 mm in accelerator
structures and 0.12 mm in quadrupole magnets. The alignment was conductedin the following way:
• Four accelerator sections, assembled with waveguides and vacuum pipes,
are pre-aligned on an 8-m steel girder, which are to be connected to an rf
source after being installed in the beamline.
• The modules are moved to the beamline by a special electric transportsystem.
• Laser beamlines are preset 420 mm below the accelerator beamline.
• The accelerator modules are aligned in reference to the laser line by using
quadrant semiconductor detectors mounted on both ends of the girder [17].
To facilitate horizontal positioning of heavy and rigid bodies, the girder is
supported using ball bearings. For vertical smoothness, the waveguides aresupported utilizing spring balances.

4

Rf system

The rf system was upgraded for KEKB. The entire rf system consists of amain-drive system, eight sub-drive systems with two stand-alone rf drivers
for the pre-injector and a positron-capture section, and 59 high-power pulsed
klystrons with modulators. A block diagram is shown in Fig. 7.

4.1

The drive system

The master frequency of the linac was 571.2 MHz; this is the 5th subharmonicof the linac fundamental frequency, and is also used for SHB2. The main drive
system [18] was newly equipped with a frequency multiplier/divider which
generates the linac fundamental frequency (2856 MHz) and the linac-ring common frequency (10.385 MHz); using this, necessary reference signals for SHB1
(114.24 MHz) and for the KEKB ring (508.9 MHz) are produced. The multiplier/divider was manufactured so as to have a very low noise performance inorder to minimize any rf phase jitter.
Eight sub-boosters, each of which drives four or eight high-power klystrons,
were reinforced to generate 60-kW rf pulses [19].
11Fig. 7. General block diagram of the entire rf system.

Solid-state 10-kW ampliﬁers were newly installed for the 114-MHz and 571MHz sub-harmonic bunchers.
A feedback controller was installed in every klystron-drive circuit to stabilize the phase and amplitude of the cw-rf signal; this stabilized signal wasmonitored and used as a phase reference [20].

4.2

General concepts for upgrading the high-power rf system

An upgrade of the linac rf power was achieved by combining a power increaseof individual klystrons and SLAC-type rf compressors (SLED). In upgrading
the linac, the existing components of the 2.5-GeV linac rf system [21] were
utilized as much as possible in order to save construction time and cost.
Regarding the rf source, it was decided that the one-pulse energy from themodulator should be doubled so that the capacitance of the pulse forming network (PFN) capacitors in a modulator would be doubled at the same charging
voltage. In this way it was possible to reuse many rf components. By doubling
the capacitance and obtaining an output-pulse width of 4 µs, most of the main
parameters of the rf system can be automatically determined. In these schemes
the required electron energy (8 GeV) is achieved along with an appropriate
number of standby tubes [22].
12

4.3

Modulator

The modulator for the 2.5-GeV old linac had been successfully operated without any serious problems [23]. A two-times increase in the PFN capacitors
at the same charging voltage required a new IVR, a rectiﬁed transformer, aﬁlter choke and a charging choke, while rectiﬁer diodes and hold-oﬀ diodes did
not need to be changed by adopting water cooling. In the PFN, two circuitswith 20 capacitors (0.0147 µF) and 20 inductors (0.33µH) each were placed inparallel. In this arrangement, smooth ﬂat-top pulses were obtained [24]. The
thyratron was also changed with ITT F-241s. Due to these modiﬁcations, themodulator cabinet of the pulse circuit section was reinforced to be larger.

4.4

Klystron and its assembly

From the requirement that any modiﬁcation of the rf system must be conducted during an interval of machine operation for the PF experiments, minimum changes to the existing system were desirable. In accordance with a
FCI [25] simulation of the previous 30-MW klystrons, producing a 50-MW
output power from the 30-MW klystron succeeded with modiﬁed high-voltage
insulation.
For more stable operation, a new 50-MW klystron having the same interaction region and collector was developed as follows. The cathode and the gungeometry were improved for higher voltage operation, but the same focusing
magnet could possibly be used with slight modiﬁcations. At the same time,
the pulse transformer was rewound to a step-up ratio of 1:13.5 from the previous one of 1:12. A heater transformer and a high-voltage insulator were newly
developed in order to use the old klystron oil tank. Therefore, we could use
the same-size klystron assembly even though the output power was increased
from 30 MW to 50 MW [26].
This klystron could output more than 60 MW for the buncher and positronsource sections under the operational condition of a shorter pulse width. The
klystron output characteristics are shown in Fig. 8. This klystron used the
BI-cathode; it has been running with a suﬃcient lifetime [27]. This tube hada single output rf window using high-density pure alumina of 99.7% with athin TiN (or TiON) ﬁlm to prevent arcing on the window [28].
13

55

70
50.6 MWFCI Prediction

51.0 MW60

40
V0 = 310 kV

35
30

FCI prediction
PV3050 #2
E3730 #225
20
15

E 373051.6 MW45

Output power (MW)Output power P0 (MW)50

0PV3050504030PV3050 #2

20
E3730 #2

10
0
200

400
800
1200
Input power (W)

240
280
320
Beam voltage (kV)360

Fig. 8. Klystron output characteristics.

4.5

SLED

The SLED cavity for KEKB was manufactured based on one of JLC-ATF witha dual-wall coupling iris (TE015 mode, Q=100000) [29]. This gave a theoretical energy multiplication factor of 2.01 maximum and 6.4 for the coupling
coeﬃcient between the waveguide and the cavity. However, 1.95 was obtained
for the multiplication factor when the rise time of the rf pulse was 100 ns andthe phase reversing time was 200 ns [30]. A schematic diagram was shown in
Fig. 9.
The entire picture of the modulator, the klystron assembly and the SLED
cavity is shown in Fig. 10.
50 MW
KLYSTRON

Upgraded
Modulator

Controller

SLED
CavitySLEDCavity3dB Hybrid

SLED RF
monitor
ACC RF Monitor

ACC

ACC

ACC

ACC

Fig. 9. Schematic diagram of the rf pulse compressor.

14

Fig. 10. The entire picture of the modulator, the klystron assembly and the SLED
cavity.

4.6

RF operation status

The operation of the upgraded rf system was started in 1998. The full rf system
has been successfully operated. In order to operate the linac stably, various
monitoring systems were also upgraded for this project.
Rf monitoring systems for power level and phase were installed in all highpower klystron modulators and are controlled with a VXI-based controller.
These enable us to diagnose eﬀectively operational problems relating to rf
sources. The stability of the master oscillator is also monitored.
Each klystron modulator is controlled with a PLC-based controller, whichmonitors interlock status and vacuum status, and also presents the historical
record of the operation data. During operation, the average rf fault rates dueto the VSWR interlock, which trips over the limiting value of 1.4 to protect therf window from failure, are about 2-3 times/hour/59 klystrons and operations
are automatically restarted after 5 seconds. When an accelerator section causes
frequent breakdowns, it is re-processed by utilizing an “auto aging program”,
installed in the PLC controller, during the idling interval between the beam
injections.
15

5

Trigger system

The trigger system is connected with the rf drive system and is constructed toprovide synchronization between the ring and linac rfs. They must be synchronized so as to meet the requirement for injection precision (+/− several-tensof picoseconds) [31].
The master beam timing-signal, which is the synchronized frequency between
the linac-rf and ring-revolution frequencies, is obtained by dividing the common frequency (10.385 MHz) by the ring harmonic number (5120). The ringrf-bucket can be selected by delaying the master timing-signal in units of thecommon clock (10.385 MHz). The gun-beam triggers are then generated bysynchronizing the master timing-signal with the linac pulse repetition signal(50 Hz at the maximum).
The trigger signals are transmitted along the linac by superposing them on
571-MHz rf signals. They are distributed to more than a hundred local pulsedrive systems, not only the electron gun but also other systems such as rf
pulse modulators and beam monitors. Received trigger signals are shaped andre-synchronized with the 571-MHz rf signals.

6

Electron pre-injector

The pre-injector consists of an electron gun, a bunching system and two regularaccelerating sections. The bunching system is composed of two subharmonicbunchers (SHBs) with frequencies set at the 25th and 5th subharmonics of2856 MHz, and a prebuncher (PB) and a buncher (B) at 2856 MHz. As described in the previous section, the pre-injector has a function which makes
the gun pulse to be a tight single bunch capable of being accelerated in the following regular accelerator sections at 2856 MHz [32]. Its operation parameters
are listed in Table 2. The main features of the components are as follows.

6.1

Electron gun

The requirements for the gun are a 200 kV accelerating voltage and 15 nC
maximum charge for a pulse width of less than 1 ns. A triode-type thermionicgun with a dispenser cathode of 2 cm2 and a high-speed grid pulser are employed for such a high current. It has a superb pulse feature of small time
jitters (σ = 4 ps) as well as short pulse lengths. It also has an electric analogue time-delay module that continuously varies the gun trigger timing over16

a 3-ns range [8]. This function is used for a digital feedback system to stabilize
the beam timing. The grid pulser also controls the beam repetition (maximum
50 Hz) with external trigger signals, as well as the beam intensity (1.2 nC and
12 nC) by changing the output voltage.

Fig. 11. Electron gun.

6.2

Sub-harmonic bunchers

The SHB frequencies are chosen from sub-harmonics near 100 MHz and 500
MHz with the condition that each frequency should be a multiple of thelinac/ring common frequency of 10.385 MHz, which is a 5 × 5 × 11th subharmonic of 2856 MHz, resulting in the 25th and 5th subharmonics.
The ﬁrst SHB operating at 114.24 MHz (25th subharmonic) and the second SHB at 571.2 MHz (5th subharmonic) are both a standing-wave type reentrant cavity with a tuning knob [9]. The dimensions are given in Figs. 12aand 12b. The rfs are fed by corresponding 10-kW solid-state ampliﬁers throughcoaxial cables.
17

EBW

φ60

coupler

φ26

vacuum port
coupler

φ180

φ198

EBW

φ40
tuner

d =42.5

tuner

L=706.84

monitor(a) SHB1
EBW

EBW

vacuum port

couplerφ26

water channel
φ24

φ45

φ198

φ180

coupler

tuner
d =30
L=706.84

tuner
monitor(b) SHB2
Fig. 12. SHB1 and SHB2.

6.3

Prebuncher and the main buncher

The prebuncher and the main buncher are both traveling-wave type diskloaded waveguides in which the phase shift is 2/3π per cell. Since the gun
beam is to be velocity-modulated at around β = 0.7, all of the cell lengths are
βλ/3 in the prebuncher, where β is the velocity in units of the light velocity,and λ is the free-space wavelength of the accelerating rf (10.5 cm). In the mainbuncher, however, the cell length varies from βλ/3 to λ/3 during the ﬁrst 6
cells, because the gun beam has to be accelerated to form a tight bunch aswell as be modulated in velocity.
As shown in the ﬁgure, the KEK prebuncher and the main buncher are assembled into one united body in order to reduce the distance between them and to
suppress the divergence due to a strong space-charge force [34]. The numberof cells is four in the prebuncher; although that in the buncher is thirty-three,bunching occurs through only the ﬁrst few cells and the β of the beam reaches
almost unity.

Fig. 13. Prebuncher and Buncher.

18

Fig. 14. Power-dividing system.

6.4

The rf power dividing system for the pre-injector

The waveguide system comprises rectangular waveguides, power dividers, phaseshifters and attenuators, which are operated in a vacuum. Typical powers fed
into the buncher sections are 1 MW (prebuncher), 23 MW (buncher), 12 MW
× 2 (two regular sections). The phase-shifter & attenuator were improved sothat the power dividing ratio between the prebuncher and the buncher andtheir phases can be varied independently [35]; this function has made it mucheasier to adjust the buncher sections.

6.5

Stabilizing the pre-injector

For stable operation, the bunch timing or phase with respect to the accelerating rf wave must be ﬁxed as well as the bunch shape. If the status of the
gun and the bunching section would become unstable, the bunch timing andshape would be changed. The tolerances for the devices are severe in the caseof a high-intensity beam of 10 nC, as are shown in Table 4. The stability inthe operation meets the requirements owing to digital feedback loops [36]. The
tolerances on the devices came from the goal of keeping the beam transmission
rate above 90% at the target.
19

Table 4
Tolerance to stabilize a high-current beam.
Beam timing± 45 psGun high voltage± 0.38 %SHB1 phase± 1.1 degree

SHB2 phase± 1.3 degree

Buncher phase± 1.7 degree

Fig. 15. Positron source.

7

Positron source

The KEKB positron source comprises a positron production target, a strong
pulsed solenoid, two 1-m accelerator sections, two 2-m accelerator sections,long DC solenoids to cover all these capture sections, and a positron/electron
separator.
The positron production target is a water-cooled 14-mm (4 radiation-length)
tungsten plate, which is able to be inserted into the beamline when a positron
beam is needed. Since the primary-beam power to hit the target became ashigh as 1.9 kW by upgrading the positron intensity, this target was newly
developed. To relax the heat stress and to maintain heat contact with thecooling channel, a tungsten-copper functionally graded material is used forthe target.
Positrons emerging from the target are focused sequentially by two types ofsolenoidal magnetic ﬁelds. The ﬁrst one is a short, strong ﬁeld of 2 T produced
20

by a 45-mm long pulsed coil [37] (so-called quarter-wave transformer). The
pulsed current (10 kA at 2 kV) is provided by a solid-state power supply. The
second is an 8-m long, 0.4-T produced ﬁeld by a DC solenoid. The positronyield and its normalized emittance are determined by the solenoid focusing
system acceptance (5.9 mm).
Captured positrons are accelerated by the following four accelerating sections
covered with the 8-m DC solenoid. The ﬁrst 1-m section has a two-iris input
coupler and large aperture disks. This structure was adopted so as to avoid any
discharge in the strong magnetic ﬁeld and strong radioactivity, which might
degrade its performance.
The positron/electron separator accommodates a chicane composed of four
rectangular magnets and a beam stopper at the center of the chicane. In
the KEK positron source, the rf phase is set so that captured positrons areaccelerated from the beginning of the ﬁrst capture section (so-called positron
acceleration mode); consequently pair-created electrons are ﬁrst decelerated,but the phase slips by 180 degrees when the electron speed decreases below
the light velocity, and they again come to be accelerated. Even in the case of
an inverse phase preset (positron deceleration mode), the situation that both
positrons and electrons which emerge from the target are accelerated is notchanged. Thus, the separator is essential to cut the electrons and to clearlyobserve the signals for adjusting the positron beam.

8

Beam instrumentation

The beam instrumentation in the linac was much improved in order to enable
operation of a high-intensity, high-stability beam for the KEKB rings. Especially, beam diagnosis to monitor and suppress transverse and longitudinalemittance growth was most important. According to a wake-ﬁeld simulation,a beam with a charge of 10 nC/bunch should be guided within transverse
positions of 0.12 mm along the center of the quads. Thus installation of beamposition monitors inside the quads was essential.
Table 5 is a list of beam monitors installed in the linac.

8.1

Streak camera

It is important to measure the longitudinal and transverse beam proﬁles atthe bunching section of the linac, since they deﬁne most of the beam characteristics. A streak-camera system was employed to measure the longitudinal
21

Table 5
Beam monitors at linac.
Type

PurposeNumberStreak Camera

Bunch Length4

Beam Position Monitor

Beam Position/Charge

90

Wall Current Monitor

Beam Charge

68

Screen Monitor

Beam Emittance/Energy-spread

112

Wire Scanner

Beam Emittance/Energy-spread

14

beam-bunch proﬁle.
Optical transition radiation produced from a polished stainless-steel plate(SUS304) is lead through an optical transport system without any distortion to a streak camera with a time resolution of 2 ps. The controls of thecamera read-out, image analysis, timing and optical systems are integrated
into an application program to ease routine measurements [38].
Systems with the same conﬁguration were installed at three other locations(just after the J-arc section, the positron-capture section and the ECS section)in order to diagnose an isochronous condition, optimum positron generation
parameters and the ECS performance, respectively.

Fig. 16. Streak-camera system installed at the pre-injector.

22

8.2

Beam-position monitor

High-current primary electron beams are required for a suﬃcient amount of
positrons, while the beam orbit must be controlled so as to suppress any beam
blow-up generated by the large transverse wake ﬁelds. Thus, a stripline-typebeam-position-monitor (BPM) system was newly developed with a resolutionof less than 0.1 mm.
Along the linac, 90 stripline-type BPMs have been attached to the pole piecesof the quadrupole magnets. The response functions of each BPM using thirdorder polynomials were determined at a test bench before installation. The
beam-based calibration was also applied with electron beams after installation.
The beam charge was calibrated using a Faraday cup with electron beams. The
beam position oﬀset against the quadrupole magnet center was determinedby varying the strengths of an upstream steering magnet and the quadrupole
magnet [39].

Fig. 17. Installed beam-position monitor.

Four signals from a BPM are connected with one of 18 measurement stations
through doubly shielded cables. At each station, those signals are delayedby appropriate delay-lines so as not to overlap each other, and are fed into
waveform digitizers of 5 Gs/s. The waveform is read through the GPIB andanalyzed with predetermined calibration factors once per second by a VME
computer. Since the timing and amplitude ranges are dependent on the beammodes, the process is driven by a control database system [40].
Acquired beam positions are sent to central computers and used by various
23beam-feedback systems to maintain stable beam operation [41].
Oscilloscope (5GS/sec)
1st BPM
2nd
Ch.2
Right

Left
Right

Left

Ch.1

Up
Up

Down
Down

Combiner
16ns Delay x 4

Combiner
16ns Delay x 4

Right
Left
Down
Up

1st BPM

2nd BPM
Beam

Fig. 18. Block diagram of the beam-position monitor system.

8.3

Wall-current monitor

Wall-current monitors have been used to measure the beam charge [42]. They
were useful to ensure the calibration factors of the BPMs described above.
Each monitor is equipped with four electrodes around it; the signals are combined to eliminate any beam-position dependence. At some locations where
the BPMs are not installed, four signals are read independently to measure
the beam position.
24

8.4

Screen monitor

Screen monitors were installed in order to observe the transverse beam proﬁle.
A compact-type monitor was newly developed to leave space for other beamline components. Screen material (Al2 O3 (99.5%) and CrO3 (0.5%)) with athickness of 1 mm was chosen so as to obtain a suﬃcient amount of ﬂuorescentlight. The screen is driven by a pneumatic actuator and controlled by a VME
computer. The beam image is viewed by a CCD camera and is sent to thecentral console room through video signal selectors.

Fig. 19. Wall-current monitor (left) and a screen monitor (right).

At about ten locations where the transverse emittance or the energy spreadshould be precisely measured, random-shutter cameras and 0.1 mm-thick screensinstead of standard ones are employed. Twiss parameters are derived frombeam-size measurements, while varying the upstream quadrupole magnets (Qscan method).

8.5

Wire scanner

Transverse emittance measurements and matching should be managed in order to transport beams. In order to carry out the tasks non-destructively,
wire scanners with suﬃcient betatron phase separations were installed. Threegroups of four wire scanners were installed before and after the J-arc section
and at the end of the linac, respectively [43]. Each wire scanner is equippedwith three tungsten wires of 0.1 mm diameter to measure the horizontal and25

vertical beam distributions and their coupling. Bremsstrahlung emitted froma wire by an electron beam is detected by a downstream photomultiplier tube.

Fig. 20. Wire scanner installed on the beam line.

A software panel was developed to automate the measurements and beamoptics calculations. The twiss parameters are measured daily and optics matching is carried out using upstream quadrupole magnets if the matching condition is not optimal.
An independent wire scanner was installed inside the J-arc section, where thedispersion is large, to measure the beam-energy distribution. Another wire
scanner was also installed just after the bunching section to measure the emittance using the Q-scan method.

9

Control system

The linac control system was rejuvenated in 1993 and has been improved
continuously [44,45]. The base of the control system comprises UNIX computers and local device controllers. The home-made RPC (remote procedurecall), based on the TCP and/or UDP protocols, are used for communication
26

between them. The overall views are shown in Fig. 21(a) and Fig. 21(b).

(a) Physical view of control system hardware.

(b) Logical view of control system processes.

Fig. 21. Block diagrams of the control system architecture.

9.1

Control Architecture

As shown in Fig. 21(b), there are three software layers in the control scheme.
The lower-layer services correspond to diﬀerent types of control hardware, suchas 16-bit binary outputs in VME computers. They represent hardware details
including error recoveries, which should be hidden from the upper layers.
The middle-layer controls are served by central Unix computers, which represent the abstract behaviors of the accelerator equipment, such as power
supplies. One middle-layer service may utilize several lower-layer ones.
The upper-layer application programs carry out actual linac operations utilizing as many middle-layer services as they need. By using the network RPC
27

scheme, upper-layer application programs can be executed by any computerson the control network, although a security measure is applied.
Several gateway programs were developed on top of middle-layer services,in order to exchange the linac information with other environments. Those
include a portable channel access server for the EPICS control environment
at the KEKB ring [46] and a CORBA interface for archived data retrieval [47].

9.2

Device controllers

While we had many old controllers which are about 20 years old, every year
new technologies are revealed. During the KEKB project, we have replaced theold controllers with new ones. The newly introduced controllers utilize VME,VXI, CAMAC, PC and PLC (programmable logic controller) technologies,
depending on the needs speciﬁc to the corresponding accelerator equipment.
Many of the controllers employ PLCs, which are directly connected to network,
if the requirement for processing speed is not critical [48].

9.3

Central computer and network

An Unix cluster server and 2 - 4 Unix computers carry out most of the
middle- and upper-layer control tasks. The cluster server system realizes afault-tolerant operation over several months.
The computer network for controls comprises an FDDI backbone (100 Mbps)
and many Ethernet segments (10 Mbps), which are linked together with astar-like topology in order to localize any problems. The connections to local
device controllers are based on the 10Base-FL Ethernet (ﬁber-optic cables),which is essential to eliminate electro-magnetic noises from the high-power
klystron modulators in pulsed operation. Important 10Base-FL segments haveredundant links for fault-tolerant network operation. While the number ofﬁber-optic connections are more than 200, the number of failures is less than
10 per year, some of which are automatically recovered by redundant links.
Besides running control-process software, Unix computers also support many
general network services, such as ﬁle services, name resolutions, remote booting, time synchronization, world-wide-web, printer and mail services. They
are important to exchange information quickly between equipment experts,
the control group and the commissioning group.
PCs running Windows operating systems are also employed for operator consoles [49,50]. They provide various linac status displays and interfaces to elec28

tronic log books.

9.4

Commissioning Software

For the linac commissioning, the following application-software environments
are used: (a) the Tcl/Tk programming language for simple operations, and(b) the SADscript [51] for advanced beam operations and studies. Both ofthem have interfaces to the control system and the Tk graphical widgets on
X-window. Many common routines are provided as libraries, such as controlsystem RPC interfaces, graphical user interfaces, operation procedures with error recovery, parameter save/restore, debugging facilities, and inter-application
communication [52].
There are more than one hundred application programs registered in the
linac commissioning software launcher, which have been updated frequently
to meet the requirements in the commissioning [53]. They include a beammode switcher, beam-energy and beam-orbit feedback systems, an emittancemeasurement and matching system, and an adaptive beam-orbit correction
program [41]. They all run online with graphical user interfaces, thus greatly
ease the commissioning.

10

Beam commissioning and operation

10.1

Commissioning

Beam commissioning has proceeded step by step since the autumn of 1997,
continuing the construction of the remaining parts as well as the ordinary injection into the Photon Factory rings (PF), even during the linac upgrade. The
design goal was fully achieved in spring, 1999, just before the detector (Belle)roll-in at the interaction point of the KEKB rings. The main achievements so
far established are the following [55]:• Fine-tuning of the pre-injector has brought about quite good performance
concerning a high-intensity primary electron beam for positron production
as well as a low-intensity electron beam for direct injection to the KEKB
ring. A 10-nC beam with a bunch length of 4.2 ps (σ) and a 1-nC beam withthat of 2.5 ps (σ) have been obtained at the end of the pre-injector witha quite good stability regarding the charge intensity and timing, ensuring
stable acceleration in the following accelerator sections (Fig. 22) [8].
29Fig. 22. Longitudinal proﬁle of the 10-nC bunch observed with a streak camera.

Fig. 23. Optical matching results in the linac.

• The optics along the whole linac was checked by measuring the twiss parameters with wire scanner monitors installed in several locations in the linac[43]. Optics matching, especially at the end of the pre-injector, in the J-arc
section, at the end of the positron-capture section and at the end of thelinac (Fig. 23) has been intensively carried out, giving satisfactory results[56].
• The beam orbit from the electron gun to the end of the linac (Fig. 24) has
been controlled with an automatic orbit-correction program, while avoiding
in particular any beam blowup due to transverse wake ﬁelds caused by beamoﬀsets.
• The energy spread of positron beams (σmeas = 0.30%) has been compressed30

Fig. 24. Beam orbit display along the entire linac length.

into a half width through the ECS (σmeas = 0.15%), reaching almost theenergy acceptance of the ring injection line (σdesign = 0.13%) (Fig. 25). The
ECS also suppresses any energy variation upstream, thus improving theenergy stability.

10.2

Operation

Since May, 1999, when Belle started to accumulate the integrated luminosity
for CP-violation measurements, the KEKB linac has been operated without
any big problems concerning injection, which could cause a long loss time
for the accumulation of the integrated luminosity (Fig. 26). The beam modeswitching [41] among four diﬀerent beams for the two KEKB rings (positronsand electrons) and two PF rings (electrons) has also worked well, giving agood reproducibility of each beam. These excellent situations are owing to
not only the result of continuing eﬀorts that the linac group has so far madeto improving each hardware component, but also the fruits of introducing
various feedback loops [54] (Fig. 27) in the orbit, energy and environmental
parameters like the temperature and electricity along the linac. One example
is stabilization of the primary electron beams for positron production, which
was one of the key issues in the ﬁrst stage of operation. We ﬁgured out thatthe stability of the beam intensity and orbit strongly depends on the timingof the grid pulser, which is, in turn, highly related to the temperature of the
gun room. The room temperature is to be regulated more precisely in the near
future, while a slow feedback loop was implemented so as to directly suppress
the timing variation of the grid pulser, resulting in good beam stability for ahigh-intensity beam. We have thus more than 30 feedback loops in operation
to assure stable injection into each ring.
31

Fig. 25. Energy width at the end of the linac.

11

Summary

The KEK electron/positron injector was successfully upgraded for the BFactory project at KEK, while maintaining injection for synchrotron-orbit
radiation experiments. To achieve 8-GeV electron beams, accelerator gain wasincreased from about 8 to 20 MeV/m as well as the accelerating modules from40 to 55. The accelerating module has been stably operated for such a highgradient. The goal of the positron intensity upgrade was also achieved by accelerating an extremely intense electron beam of nearly 10 nC. To stabilizeit, many beam-monitors and rf/timing monitors was newly constructed anda computer-controlled beam operation/feedback system were extensively developed. While switching beams into four kinds of rings, all beams are being
injected smoothly. The injection time for the KEKB rings are adequate tointegrate the luminosity for B-physics experiments.
32

Fig. 26. Accumulation of the integrated luminosity.

Acknowledgment
The authors greatly appreciate Dr. G. Voss, who was the chairman of the
KEKB accelerator review committee, and other members, especially Dr. J. Seeman and Dr. S. Wang, for helpful advice and encouragement for several years
during the linac upgrade.

References[1] J. Tanaka et al., Nucl. Instr. Meth. 177, 1980, pp.101-105.
[2] I. Sato, Nucl. Instr. Meth. 177, 1980, pp.91-100.
[3] J. Tanaka et al., Proc. of the 1984 Linear Accelerator Conference, Darmstadt,
Germany, 1984, pp.475-479.
[4] A. Enomoto et al., Nucl. Instr. Meth. A281, 1989, pp.1-9.

33

Fig. 27. Feedback loops.
[5] A. Enomoto, Proc. of LINAC96, Geneva, Switzerland, 1996, pp.633-637.
[6] A. Enomoto et al., Proc. of EPAC2000, Vienna, Austria, 2000, pp.993-995.
[7] Y. Ogawa et al., Proc. of LINAC94, Tsukuba, Japan, 1994, pp.535-537.
[8] S. Ohsawa et al., Proc. of EPAC2000, Vienna, Austria, 2000, pp.845-847.
[9] S. Yamaguchi et al., Proc. of LINAC98, Chicago, IL, USA., 1998, pp.558-560.
[10] J.Y. Choi et al., Proc. of LINAC96, Geneva, Switzerland, 1996, pp.340-342.
[11] T. Kamitani et al., Proc. of LINAC94, Tsukuba, Japan, 1994, pp.190-192.
[12] D.C. Carey et al., SLAC-R-95-462, 1995.
[13] S. Yamaguchi et al., Proc. of LINAC96, Geneva, Switzerland, 1996, pp.346-348.
[14] T. Oogoe et al., Proc. of LINAC94, Tsukuba, Japan, 1994, pp.266-268.
[15] S. Yamaguchi et al., Proc. of APAC98, Tsukuba, Japan, 1998, pp.136-138.

34

[16] K. Kakihara et al., Proc. of LINAC94, Tsukuba, Japan, 1994, pp.567-569.
[17] Y. Ogawa et al., Proc. of PAC95, Dallas, 1994, pp.567-569.
[18] H. Hanaki et al., Proc. of APAC98, Tsukuba, Japan, 1998, pp.139-141.
[19] S. Fukuda et al., Proc. of LINAC96, Geneva, Switzerland, 1996, pp.187-189.
[20] H. Katagiri et al., Proc. of APAC98, Tsukuba, Japan, 1998, pp.142-144.
[21] S. Anami et al., Proc. of the 1981 Linear Accelerator Conference, Santa Fe,
New Mexico, USA, 1981, pp.177-179.
[22] S. Anami et al., Proc. of the 9th Symp. on Acc. Sci. and Tech., Tsukuba, Japan,
1993, pp.125-127.
[23] T. Shidara et al., Nucl. Instr. and Meth., A279, 1989, pp.423-432.
[24] H. Honma et al., Proc. of LINAC94, Tsukuba, Japan, 1994, pp.436-438.
[25] T. Shintake et al., Nucl. Instr. and Meth., A363, 1995, pp.83-89.
[26] S. Fukuda et al., Nucl. Instr. and Meth., A368, 1996, pp.561-571.
[27] S. Fukuda et al., Applied Surface Science 146, 1999, pp.84-88.
[28] S. Michizono et al., Applied Surface Science 169-170, 2000, pp.742-746.
[29] H. Matsumoto et al., Nucl. Instr. and Meth., A330, 1993, pp.1-11.
[30] H. Hanaki et al., Proc. of EPAC96, Barcolona, Spain, 1996, pp.2003-2005.
[31] KEKB B-Factory Design Report. 1995, Chap.12, p.30.
[32] S. Ohsawa et al., Proc. of LINAC94, Tsukuba, 1994, pp.193-195.
[33] S. Yamaguchi et al., Proc. of LINAC98, Chicago, USA., 1998, pp.558-560.
[34] S. Ohsawa et al., Proc. of PAC93, Washington D.C., USA., 1993, pp.3087-3089.
[35] S. Ohsawa et al., Proc. of LINAC90, Albuquerque, NM, USA., 1990, pp.159-161.
[36] S. Ohsawa et al., Proc. of PAC2001, Chicago, Illinois, USA., 2001, to be
published.
[37] S. Ohsawa et al., Proc. of HEACC92, Hamburg, Germany, 1992, pp.135-137.
[38] Y. Ogawa et al., Proc. of APAC98, Tsukuba, Japan, 1998, pp.534-536.
[39] T. Suwada et al., Nucl. Instr. and Meth. A440 (2000) 307.
[40] N. Kamikubota et al., Proc. of ICALEPCS99, Trieste, Italy, 1999, pp.217-219.
[41] K. Furukawa et al., Proc. of LINAC2000, Monterey, CA., 2000, pp.633-635.
[42] T. Suwada et al., Nucl. Instr. and Meth. A396 (1997) 1.
[43] N. Iida et al., Proc. of EPAC2000, Vienna, Austria, 2000, pp.1738-1740.

35[44] K. Furukawa et al., Proc. of ICALEPCS91, Tsukuba, Japan, 1991, pp.89-92.
[45] N. Kamikubota et al., Nucl. Instr. and Meth. A352 (1994) 131.
[46] K. Furukawa et al., Proc. of ICALEPCS95, Chicago, USA., 1995, pp.863-866.
[47] N. Kamikubota et al., Proc. of ICALEPCS97, Beijing, China, 1997, pp.351-353.
[48] K. Furukawa et al., Proc. of ICALEPCS97, Beijing, China, 1997, pp.146-149.
[49] K. Nakahara et al., Nucl. Instr. and Meth. A293 (1990) 446.
[50] I. Abe et al., Proc. of ICALEPCS97, Beijing, China, 1997, pp.519-521.
[51] <URL:http://acc-physics.kek.jp/SAD/sad.html>.
[52] K. Furukawa et al., Proc. of ICALEPCS99, Trieste, Italy, 1999, pp.98-100.
[53] N. Kamikubota et al., Proc. of APAC2001, Beijing, China, 2001, to be
published.
[54] K. Furukawa et al., Proc. of ICALEPCS99, Trieste, Italy, 1999, pp.248-250.
[55] Y. Ogawa et al., Proc. of Factories99, Tsukuba, Japan, 1999, pp.64-69.
[56] T. Kamitani et al., Proc. of APAC98, Tsukuba, Japan, 1998, pp.429-430.

36