The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

Design of the RIKEN-SRC RF System
Naruhiko SAKAMOTO, Osamu KAMIGAITO, Akira GOTO, Yoshitoshi MIYAZAWA, Toshiya Chiba,
Hiroki Okuno, Toshinori Mitsumoto, Yasushige YANORIKEN, 2-1, Hirosawa, Wako-shi, Saitama 351-01, Japan
Abstract

The acceleration and flat-top resonators for theRIKEN Superconducting Ring Cyclotron (SRC)[1] arerequired to work in a wide frequency range with a highacceleration voltage. To satisfy the requirement, a design study has been made by using a three dimensional rf calculation code MAFIA[2] as reported in ref [3].
Recently, since a rearrangement of the injection and extraction devices was made[4], the configurations of theresonators has been reconsidered.
1 Introduction

For the RIKEN RI-Beam factory (RIBF) [5] thenew booster ring cyclotrons, intermediate-stage ring cyclotron (IRC) and superconducting ring cyclotron, areplanned to be constructed to boost the energy of heavy
ion beams from the RIKEN ring cyclotron (RRC) tothe intermediate energy region of 60~400 MeV /u witha beam intensity of 1 pfJA 1 .
The SRC requires acceleration resonators having awide frequency range from 18 to 38.2 MHz to suit thecondition of the RRC operation.
The maximum magnetic field of the SRC sector magnet is as large as 4.2 T. Due to the strong magnetic fielda high acceleration voltage is also required to obtain alarge turn separation. A large turn separation aroundthe extraction is crucial to reduce the beam losses atthe extraction devices. For example, in the case of the16 07+ ion acceleration up to the maximum energy of 400MeV /u at the rf frequency of 38.2 MHz with a harmonic
number h=6, an acceleration voltage of 2.4 MV /turn isneeded to obtain a turn separation larger than 4 mm at
the extraction orbit.
A flat-top system is also helpful to reduce the beamlosses at the extraction because the energy spread of theaccelerated beam can be reduced by a flat-top acceleration. The phase acceptance D.¢, which is defined byIV(D.¢)1/V(¢ = 0) :-=:; 10-4 , for the nonflat-top acceleration and flat-top acceleration are ±0.81 o and ±7.3°,
respectively.
In order to realize a large turn separation,• Four acceleration resonators which are single-gap
type are employed.

Table 1
Key parameters of the acceleration and the flat-top
resonator for the SRC
flat-topaccel.
resonators
14
No. of units
85.97 ~ 114.6
18""' 38.2
Frequency[MHz]single gap
Ace. gap
120250[mm]
Aperture[mmxmm]flapping panel shorting plate
Coarse tuner
500~1100 mm
oo ~ 90°
Tuner stroke
block tuner
Trimmer
inductive loop
Feeder0.360.6
Max. VP [MV /gap]
1o- 3
10- 4
Voltage stability±0.3°±0.1 °Phase stability
4381Max. Power [kw]
25000
37000
Q-values

flat-top resonator has been moved from the center regionof the valley chamber to the next to the acceleration resonator (see Fig. 1), a new design of the flat-top resonatorhas been introduced. The dimension of the accelerator
resonator also has been rearranged.
For the flat-top system the third, fourth, and fifth
harmonics are used. It is helpful for the mechanicaldesign of the flat-top resonator because the frequency
range becomes narrower. The frequency range of thenew flat-top resonator is 85.97~114.6 MHz instead of
54.0~114.6 which is for the third harmonic system. The
phase acceptances of the fourth and the fifth harmonic
fat-top system are large enough (Fig. 4) to accept thebeam from the RRC.

+

• The peak voltage of the resonators is set to be 600
kVp/gap.

:::::sl\• A flat-top system is employed.
The key parameters of the present design of the resonators are listed in Table 1. Since the location of theRES3~.>:Fig. 1 Top view of the acceleration resonatorand the flat-top resonator.

1 particle micro ampere~221 ~"17!

The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

~~:

:

~

Table 2The calculated rf characteristics of the acceleration
resonator by using MAFIA.

~··-+---+- no-~flattiop· +· ···· :·--:--7n~3;.. -·+----~- '1E. ~ ·4 _;_~.'.

''.!:.

n !"= 5 ~Flapping Panel
Frequency [MHz]Q-valueRs [MO]Vp [kV]
Pw.I. [kW]~g 1.0000

~;

..!..

0.9998~0 deg .
17.47428200
0.6325050

90 deg.
38.607366492.23
60081!

-w

3 Flat-top resonatorwo~ (degrqe)

Fig. 2 Acceleration voltage w1tn a flat-top resonator.
l:i¢ = IV(/::i¢)1/V(¢ = 0):::; 10-4

2 Acceleration resonator

The acceleration resonator is a single-gap type whosestructure is basically same as that of the RCNP Ring
Cyclotron(RCNP-RC)[6]. The single-gap type resonatoris suitable the for the narrow valley section of the 6sector ring cyclotron because its size is compact compared with the double-gap type resonator.
The rf characteristics of the acceleration resonatorare obtained at the flapping panel positions of 0° and90° by using MAFIA as shown in Table 2. Since theQ-value and the shunt-impedan ce of the real resonatoris expected to be 60--.,70 % [7] of the theoretical values,
the maximum wall loss of the real resonator is estimatedto be 115--.,135 kW.

The new design of the flat-top resonator for the SRC
is shown in Fig. 4 The resonant frequency tuning is madeby moving the shorting plates which are placed symmetrically with the median plane. By utilizing the multiharmonic numbers of 3, 4, and 5, the required frequency
range becomes 85.97--.,114.6 MHz. As shown in Fig. 5
the frequency range is successfully covered by moving
the shorting-plate from 500 to 100 mm with large Qvalues. The maximum wall loss is estimated to be 85
kW if the Q-value of the real resonator was 50% of thetheoretical value.

0MM

Ltl
00Ltl

10

....

Fig. 4 Schematic dra
2140- - --f---·--·SRC FT-RESONATOR

~

J,00

N5-1---M

panel

25000

--r-~lFig. 3 Schematic drawing of the acceleration resonator. Resonances with the lowest and highest resonant frequencies are obtained when theflapping panel is horizontal(0°) and vertical(90°), respectively.

15000

01250
1000
750
500
250,POSiiiO!)l of thq. s!q>rt-platp [m] •

10000
1500

Fig. 5 The crucu ated n cnaractenstics of the flat-top
resonator by using MAFIA.

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4 Amplifiers and Transmission lines

obtained. Further investigation on the feasibility of theresonator design will be made.

The main parameters of the rf amplifiers are listed
in Table 3. The design of the final stage amplifier for theacceleration resonator is the same as that of the RRC.
Since the transmitter tubes do not work in the strong
magnetic field, the amplifiers are planned to be placed
where the leakage field of the SRC sector magnets becomes smaller than 50 Gauss. The length of the powertransmission lines is estimated to be 50 m.

The authors are grateful to Mr. Y. Kumata for useful
discussion on the design of the resonator and the amplifiers.

Table 3Characteristics of the RF amplifier

References

Frequency
1st stage
2nd stage
power
Final stagepower
Trans. line

[MHzJ
[kW]
[kWJ[kW]

acceleration
flat-top
18.0 rv 38.2 85.97 rv 114.6
11
RS2012CJ
155RS2042SK
RS2058CJ
300
100
WX152D/500

5 Summary

A design study of the SRC rf system has been made.
According to the rearrangement of the SRC, new designsof the acceleration and the flat-top resonators areAcknowledge ment

[1] A. Goto et al., "Construction of the RIKEN Superconducting Ring Cyclotron", in this paper.
[2] The MAFIA collaboration, User's Guide MAFIA
Version 4.0, CST GmbH, LauteschagerstraBe 38, D64289, Darmstadt, Germany.
[3] N. Sakamoto et al., Proc. 15th Int. Conf on Cyclotrons and Their Applications, (Caen 1998), p 223.
[4] H. Okuno et al., "Design study of the Injection andExtraction Systems of the RIKEN Superconductin g
Ring Cyclotron", in this paper.
[5] Y. Yano et al., Proc. of 1997 Partl. Accel. Conf.,
p.930.
[6] T. Saito et al., Proc. 12th Int. Conf. on Cyclotrons
and Their Applications (Berlin 1989), p. 201.
[7] N. Sakamoto et al., "Model Test of the RIKEN-IRC
Main Resonator", in this paper.

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