JAERI-Conf 95-021

PA18

RF system of SPring-S Linac
Shinsuke SUZUKI, Hiroshi YOSHIKAWA, Toshihiko HORI, Tsutomu TANIUCHI,Kenichi YANAGIDA, Akihiko MIZUNO, Atsushi KUBA, Yuichi ITOH,Hironao SAKAKI, Masahiko KODERA, Hideyoki KOTAKI, Takashi OKADA
and Hideaki YOKOMIZOThe SPring-S Project TeamThe Japan Atomic Energy Research Institute (JAERI), Kamigori, Hyogo 678-12, JapanAbstract
The construction of the SPring-8 linac (2856 MHz,60 pps) was started in 1991 March. In 1993, we modified the design of Linac RF system. We choose new
80 MW klystrons, instead of 35 MW klystrons. With
this situation, RF power from one klystron is led to
two accelerating structures, instead of one accelerating structure. This linac is composed of 13 highpower klystrons and 2 medium power klystrons with
26 accelerating structures.

I. INTRODUCTIO N
The 2856 MHz RF system of SPring-8 linac
is shown in Fig. 1. This system is composed ofthree systems. One is the injector (buncher andpre-bunchers) line and the driver system of main
klystrons by the booster klystron. The injector line
is already completed and tested in Tokai establishment of JAERI [1]. This system ware transferredfrom Tokai to Harima in summer 1995. Next is thephase measurement system with the reference line.
Last is the high power RF system with wave guidecircuit. There are required the phase stability of2 degrees on the beam line.

II. BOOSTER KLYSTRON AND DRIVE
LINEThe 2856 MHz low-level CW output of a highly
stable master oscillator is divided into two signallines. One is provided for the booster klystronthrough a pulse modulator and a 300 W TWT amplifier. The other provides for the reference line throughthe 1 W CW amplifier to the phase measurement system.
The output of the booster klystron is fed into theinjector line (two prebuncher and buncher). Driveline is divided by a 6-dB directional coupler from injector line. The injector line is filled with 2 kg/ cm2SF6 gas. In the drive line, about an 1 MW RF powerthat controlled by DR</>A with SF6 gas is provided inplesured dry air at 2 kg/ cm2 • Each fo these klystrons

are driven by RF (about 1 kW), branched by directional coupler, from the drive line with I</>A (Isolator,Phase shifter, Attenuator).

III. PHASE MEASUREMEN T SYSTEM
For high stability beam control, the RF systemneeds phase measurement and feedback system. Thedrive line consists of an 120 m length copper wave
guide. The phase of the drive line for last klystrondrifts by 11.2 degree;oc. For correction of the phasedrift, <J>CMP detects a phase drift by comparing withthe standard phase of the reference line.
The reference line is the phase stabilized coaxial
cable (Mitsubishi Cable). Electrical length of thiscable is stabilized at 2 PPM/°C (0.5 degreefCC at140 m). The standard phase of the reference line ispicked up from the long pulse beam (or the monitor directional coupler of the buncher). The beamphase after HO accelerating structure is detected by awaveguide type pickup cavity (only long pulse mode).
It is the duplicated reference line through phaseshifter after the CW amplifier. The phase drift thatis detected by </>CMP is corrected by VME controlledI</>A before each klystron. This system will be available within 2 degree phase drift.
The </>CMP is composed by phase discriminator(Anaren 2A0756) and phase shifter. The phase discriminators compares with the output of the forward
acceleration structure of main klystron and the standard phase of the refarence line. After beam tuning(beam is on the best phase), phase shifter adjust tozero-cross point for avoiding the effect of RF power
strangth. When the input RF phase of acceleration
structure is drift, the phase discriminator detect thephase shift. Output of the phase discriminator after
sample hold is fed the VME analogue modules. The
VME control the I</>A of the klystron input of thedrive line.
When the linac was driven in the long pulse (1 JJSbeam width) mode, the beam phase with the pickup
cavity can duplicate to the refarence line using thephase shifter after the CW AMP in Fig.l. On theshortpulse or single pulse mode, we will use the-73-

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targetFig. 1. RF system of SPring-S Linac
Solid line is high power line. Dashed line is monitor line.
HO""'M19 :number of accelerating structure, KLY :klystron, 1><1: RF window<P : phase shifter, DR<PA : phase shifter and Attenuator for drive line
I</JA : isolator, phase shifter and Attenuator, </JCMP : phase drift detector
buncher input phase instead of the pickup cavity.

IV. HIGH POWER RF SYSTEM
The first accelerating structure (HO accelerating structure in Fig. 1) is powered by one 80 MW
klystron (Toshiba E3712). After the second accelerating structure, the RF power from one 80 MW
klystron is divided by a 3 dB directional coupler,and fed to two accelerating structures exclude thee+ fe- converter section. It is important to control
optimized phase and power for the positron converter
section [2]. The accelerator structure of the converter
section (M1 section in Fig. 1) is driven by the 35 MW
klystron (MELCO PV3035) as 1:1 drive.
For a 1.15 GeV electron beam, the RF power of26 MW is fed into all accelerating structures that
produce an electric field gradient of about 16 MeVfm.
As we have some margin when one or two klystrons
faults, we should keep the linac energy for injection
by the rest klystron.

Each klystron is driven by traditional a 190 MW
pulse modulator [3] with a flat top of 2 J.lS within
the voltage fluctuation of ±0.5 % at 60 pps. This
modulator output will be lead to main klystron withthe 1:16 pulse transformer. The voltage stability ofPFN charging is achieved of ±0.5 % using the DeQ'ing method.
Wave guide circuits is composed of RF windows,
3 dB directional couplers, vacuum pumps and phaseshifters. As the wave guide is fevered by about 50 °C
increment at 80 MW without cooling, it is cooled bywater of the ordinary water cooling system. En one
side route to behind the 3 dB directional coupler, ahigh power phase shifter is prepared. By this, eachphase of accelerating structure can be controlled.
Recently, the high power test of the wave guidecircuit was carried out by Toshiba Co'. The result
and the photograph are shown in Fig 2 and Fig 3 [4].
A large RF power up to 80 MW-4 J.lS-60 pps shall passthrough the wave guide system. Critical components-74-JAERI-Conf 95-021

ator Conference, Washington, Vol 1, p.602{1993)
S. Suzuki et al., "Construction of SPring-S Linac",
Proceedings of the 1994 Fourth European Particle Accelerator Conference, London, Vol1, p.733(1994)[2] A. Mizuno et al., "Test and Simulation of the Positron
Converter for SPring-S Linac", Proceedings of the 9th
Symposium on Accelerator Science and Technology,
Tsukuba, p.122(1993)
A. Mizuno et al., "SIMULATION OF POSITRONFOCUSING SYSTEM FOR SPring-S LINAC", Int.
J. Mod Phys. A (Proc. Suppl.) 2A(1993), Proceedingsof the HEACC'92, Humburg, Vol 1, p.132(1992)[3] A. Mizuno et al., "Modurators for SPring-S linac", inthis condfarence~~uu~~~~~~~~~o100

zoo300400soo[4) K. Satoh et al., "HIGH POWER TEST OF S-BAND
WAVE GUIDE SYSTEM FOR THE SPring-S INJECTOR LINAC", Proceedings of the 20th Linear Accelerator Meeting in Japan, Osaka, Vol 1,p.263(1995)

TIME (hour)Fig. 2. Result of high power testFig. 3. Photo of high power test
such as ceramic-RF-window and a phase shifter areadopted in this high power system. After 420 hours
aging process a stable operation with the maximum
RF power was realized. Especially, the high power
phase shifter was operated in the full RF power without breakdown.

V. CONCLUSION
The installation of the linac is started in May,
1995 in Harima. RF system will be started to installin October, 1995. The aging of the waveguide circuits
will be started in April, 1996. And t]:le first beamcommissioninng of this linac will start at the first ofAugust 1996.
References[1) S. Suzuki et al., "Initial data of Linac Preinjector for
SPring-S", Proceedings of the 1993 Particle Acceler--75-