JAERI-Conf 95-021

PA12
RF SYSTEMS OF SYNCHROTRONSFORJAPANESE HADRON PROJECT
Chihiro OOMORI, Munetaka FUJITA, Yoshiharu MORI,
Hitoshi NAKAYAMA, Masashi SHIRAKATA*, Akira TAKAGI*, Makoto TODA*,
Tetsumi TANABE, Yoshio TANABE and Masahito YOSHII*
Institute for Nuclear Study, University of Tokyo
Midori-cho, Tanashi-shi Tkyo 188 JAPAN*National Laboratory for High Energy Physics, KEK, Tukuba ,lbaraki- ken, 305 JAPAN
Abstract
Conceptual designs of the RF systems forboth 3 Ge V and 50 Ge V proton synchrotrons aredescribed. The RF systems provide an acceleratingvoltage per station of 40 kV because of a highaccelerating rate, and also the systems are
required to be stable for the heavy beam loading toaccommodate high intense proton beam accele.ration. In order to reduce enormous beam loading,a low plate-resistanc e tetrode and a fast feedback
technique are considered to use.

per pulse) is designed to be accelerated. The
circulation beam current in the main ring is about
twice larger than that in the booster, the beamloading effects in the main ring acceleration
become more serious than in the booster.
In both the synchrotrons, for stableaccelerations of high current beams, the reductionsof heavy beam loading effects must be dispensable.
The main parameters of both the ringssummarized in Table 1.

II. RF System for The Booster
I. Introduction
A. Cavity and RF-statioli

Accelerator complex for the JHP is locatedin the KEK site and consists of four accelerators:
pre-injector, 200 MeV linac, 3 GeV booster and 50
GeV main ring synchrotrons!) .
The booster is a rapid-cycling proton
synchrotron and will be constructed in the present
KEK-PS tunnel. The booster magnet is excited byusing a resonant network 2)_ The repetition rate of
the booster is 25 Hz, in future 50 Hz operation isscheduled. A circulating average beam current in
the booster is designed to 200 J..LA. The beam is
supplied to the adjacent 3 experimental facilities!)
as well as injected into the 50 GeV main ring.
Because of a high repetitive operation, a sweep-rateof rf-frequency and an accelerating voltage needs
to be high. The RF harmonic numbers of both rings
are 4 and 34, respectively. Thirty-two bunches fromthe booster are injected into the main ring.
The main ring synchrotron is located on thenorthern part of the KEK site. The size of ring isabout four times larger than that of the booster ring.
The main ring synchrotron operates in a cycle of 6
seconds; the accelerating period is 2.5 seconds. The
main ring synchrotron is also a high current beam
accelerator. Proton beams of 4 x 1014 ppp (particlesThe requirements for the high intensity andrapid cycling synchrotron determine many
parameters on the RF system. In the case of thebooster, a fast time-response for tuning a cavity andto minimize a heat power loss in the cavity should berequired.
The rf-frequency range is from 2. to 3.4
MHz, at the request of experimental users. For thisfrequency range, a ferrite-loaded re-entrant cavity
is practical. The number of the rf-stations is 10 andthe length of the station is 3 m. One rf-stationconsists of four quarter-wave coaxial lines, there is
two accelerating gaps to obtain the required
acceleration voltage .
Under the conditions of maximum acceleof 220 GeV/sec and an intensity of 5 xrateration
1013 ppp, the beam consumes a maximum peak
power of 180 kW per rf-station. An accelerating
voltage of 40 kV per station must be required at asynchronous phase angle of 45 degrees.
The design of cavity strongly depends on thechoice of ferrite materials. A J..LQf-product (J..L:relative permeability of a ferrite, Q: quality factor
of a ferrite and f: operation frequency) is one of thekey parameters when the cavity impedance is-55-JAERI-Conf 95-021

determined. A shunt impedance (Rsh) in an
equivalent circuit of the resonant cavity is givenby;
Rsh=UJLQocJ.lQJ ·( 1)On the other hand, the beam current flows in
the opposite direction of the generator current. The
beam induced voltage acts on decelerating thebeam .. The maximum peak current of circulating
beam IS 7 amperes. Though its fundamental fouriercomponent (lb) depends on the bunching factor andthe longitudinal distribution, its maximum value
is twice of the peak current and 14 amperes. This
enormous beam current affects on all the RF systemthrough the accelerating gaps and feedback
systems. The stability for the beam loading isestimated by a relative beam loading Y, Y=Ib/I 0
where Io is an RF generator current to give the sam~gap voltage without beam load and with cavity tuned
to resonance and equals to shunt-resistor current3). For stability Y must be less than 2. In order toreduce the relative beam loading, a low plateresistance tetrode is considered· to use because theresonant cavity resistance can be reduced.
In our design, for instance, the required RF
generator current is - 10 amperes; Y = 1.4. Peakpowe~ loss in ferrites is set to be -200 kW per cavity.
In th1s case, the shunt impedance of 4000 n andferrite materials of which minimum IJ.Qf-value isgreater than 4 x 109 , would be necessary.

B . Feedback System
The rf-generator current Io is smaller thanthe circulating beam current. Specially, during thebeam capture process in the booster, because theaccelerating voltage should be low to avoid alongitudinal emittance growth. The relative
loading Y becomes larger and the beam loading
effects grows big. To reduce such loading effects,

several rf-feedback systems must be considered tocontrol the accelerating rf-system in stable3).
For the resonant cavity, beam induced
voltage (Vbeam) is;v;,eam = -Reff.sh • Jb,(2)where Reff.sh is an effective shunt impedance
which is an impedance seen from a beam. The
effective shunt impedance must be reduced tominimize the beam induced voltage.

III. RF System for The Main Ring
In the 50 GeV main ring, the rf-frequency is
swept 3 % during the acceleration, and the average
acceleration rate is - 20 GeV/second which is ten
times less than the booster acceleration rate.
However, the beam loading current in the main

ring is more than twice larger than in the booster.
The choice of ferrite materials and the design,
which take into consideration such a heavy beamloading, are very important.

A. Cavity and RF-station
The number of the rf-stations is 5 in themain ring. As the accelerating rate is - 20
GeV/second, the required accelerating voltage is 40
kV per rf-station at the synchronous phase angle of30 degrees. The rf-frequency is swept from 6.86 to
7.07 MHz. The beam intensity is 4 x 1Q14 ppp. Thecorresponding peak current is -13 amperes.
Considering twice of the peak current as the beamloading current, even if the relative loading Y
allows 2, the generator current becomes larger thanthat in the booster. The RF feedback system isdefinitely required to compensate such a heavy
beam loading.
Table 2 summarizes RF parameters for boththe booster and main rings.

IV. Summary
In the recent high intense proton synchrotrons, the beam current inclines to be larger than
the generator current. Nevertheless, the ferriteloaded resonant cavity is the most practical as atunable cavity in the frequency regime of several
mega-hertz. In those ferrites, the heat loss limits toincrease the generator current and RF voltage,
because the quality factor and the curie point offerrite materials are relatively low.
In FY1995, we have started to examine theferrite materials. In these examinations, the basic
parameters of loaded ferrites will be cleared.
The preliminary design for the RF systems
for both 3 GeV booster and 50 GeV main ring
synchrotrons are described. As the performances offerrite materials are not clear, the design is limited
at this moment.
The author thanks all members of the KEKPS groups for useful discussions and theirencouragement.

V. References[1) Y.Mori et al., "Outline of JHP Synchrotron
Design", in this proceedings.
[2] T.Adachi el al., "Design of Magnets and Power
Supplies of 3 GeV Booster for Japan Hadron
Project", in this proceedings.
[3] F. Pedersen, "Beam Loading Effects in The
CERN PS Booster", IEEE Trans.Nucl. Sci. vol. NS22, No. 3, June 1975.

-56-JAERI-Conf 95-021

Table 1
Specifications of the booster and main ring synchrotrons

CircumferenceTransition gamma
Beam energy
Bp~yinj. I ext.
inj. I ext.
inj. I ext.

3 GeV Booster

50 GeV Main Ring

339.4m6.25
200 MeV/ 3 GeV
2.15 I 12.8 Tm
0.687 I 4.081442m
27 i (imaginary)
3 GeV /50 GeV
12.8 I 170 Tm
4.07 I 54.3

0.50 I 0.86 MHz
25Hz (50 Hz)
20 msec
220 GeV/sec
5 x1o13ppp*
200 !lA
4-7A
0.6 MW

0.20 I 0.21 MHz
6 sec
2.5 sec
20 GeV/sec
4x1o14ppp
10 !lA
13 A

Revolution frequency
inj. I ext.
Repetition rate
Accelerating period
Accelerating rate
Number of particles
Beam current
Circulating current (peak)
Beam power*protons per pulse

Table 2RF parameters of the booster and main ring synchrotrons
No. of acceleration gap per station
Max. rf-voltage per gap
Max. phase angle
Accelerating voltage
Number of RF stations
RF harmonic number
RF frequency sweep range
Length of rf-station
Diameter of beam pipe
Duty Cycle

3 GeV Booster
220kV
45 degree
400kV
1042.00- 3.43 MHz
3m
20cm
50%-57-50 GeV Main Ring
220kV
30 degree
200kV
5346.86 - 7.07 MHz
3m20cm
42 % (2.5 sec./6 sec.)