The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

An energy upgrade of RIKEN Heavy Ion Linac
Eiji Ikezawa, Masayuki Kase, Nobuhisa Fukunishi, Masaki Fujimaki, Osamu Kamigaito,Shigeo Kohara, Toshimitsu Aihara, * Tomonori Ohki, * Hi roo Hasebe, * Hiromoto Yamauchi,*Akito Uchiyama,* Yoshitomo Uwamino, Akira Goto, and Yasushige Yano
The Institute of Physical and Chemical Research (RIKEN),
2-1, Hirosawa, Wako-shi, Saitama 351-0198 Japan* SHI Accelerator Service, Ltd.

1INTRODUCTION

The RIKEN heavy ion linac (RILAC) started to supply
beams for experiments in 1981 [1Jand to inject them to theRIKEN ring cyclotron (RRC) in December 1986. Themaximum beam energy of the RILAC is 4 MeV/nucleon.
A PIG ion source installed in the450 kVCockcroft-Walton
injector was replaced with an 8-GHz ECR ion source(NEOMAFIOS) in fall of 1990 [2]. A new system
consisting of a variable-frequency folded-coaxial RFQ linac[3) and an 18-GHz ECR ion source 14) was installed as thesecond pre-injector to the RILAC in 1996. The both preinjectors had been used depending on requirement ofexperiments since January 1997.
In the RIKEN RI-beam factory (RIBF) project, aCharge-State Multiplier (CSM) system has been proposedin order to increase the charge state of the ions that are
injected into the RRC [5). In 1999, the first unit of theCSM, consisting of two acceleration cavities and one
deceleration cavity, has been constructed 16]. In 2000, in acollaboration between RIKEN and the Center of Nuclear
Science (CNS) of Tokyo University, the rest of four
acceleration cavities were constructed f7]. These six cavities
were installed just after the RILAC as a booster of theRILAC in summer of 2000. The maximum beam energy,
which is boosted by the CSM, is 5.8 MeV/nucleon. Themaximum beam intensity assumed is 10 p!iA.
To utilize the beams accelerated by the RILAC or theRILAC + CSM for various experiments, the beam transportsystem of the RILAC facility has been replaced to the newone. One of the most important experiments proposed hereis the search of super-heavy elements via a sub-barrier
fusion reaction. It has been decided that, for the next twoyears until the first phase of RIBF will start, a stand-alone
use of the RILAC using the booster cavities of the CSM isplanned for the research of super-heavy elements.

2BOOSTERThe six booster cavities and one deceleration cavity havebeen installed just after the RILAC as shown in Fig. 1. The
first two booster cavities (CSM AI, A2) and the last

deceleration cavity (CSM D1), which form the first unit ofthe CSM, were fabricated with a full specification. They areof variable-frequency type, being tunable from 36 to 76.4
MHz. The other four booster cavities (CSM A3"-' A6) weremade without a frequency tuner to save a cost. They areoperated at a fixed frequency of 75.5 MHz. This frequency
was selected to set the maximum energy at 5.8
MeV/nucleon which is required by the research of superheavy elements.
The operational radio-frequencies are twice as that of theRILAC to double the acceleration gradient. The required gap
voltages are approximately 500 kV. The total voltage-gainof the booster cavity is 16 MY, which is the same as that ofthe RILAC. The ions which have a mass-to-charge ratio ofless than 5.6 are accelerated up to 5.8 MeV/nucleon.
Each cavity is equipped with a turbomolecular pump of520 1/s and a cryogenic pump of 4000 1/s. The vacuum stays
in the range of0.5-1.0 X 10·7 Torr in the cw-mode operation.
High-power tests of the cavities have been perfonned
since September 2000 [8].

3NEW BEAM TRANSPORT SYSTEM

The beam transport system of the RILAC was modified
in order to insert the CSM system between the RILAC andthe RRC. The new beam transport system is illustrated inFig. 1. It has one main line and six branches. The main linetransfers ions from the RILAC to the RRC via the CSM.
The bending magnet BM90 separates the desired charge statefrom others by utilizing the difference in magnetic rigidity.
Four successive dipole magnets (SW, BA-A, BA-B andBM85) bend the beams further. The total bending angle is355 degrees. This structure produces a space for thedecelerator section of the CSM which will be installed in thefuture. The ions are transferred to the RRC using theexisting beam line. The section from the charge stripper tothe decelerator is designed to be achromatic and isochronous
like a ring cyclotron. These features are effective to avoid
complicated coupling of the longitudinal motion driven by
the CSM and the horizontal motion caused by the beam linemagnets.

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The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

11

c=,==~=~~~='U"_jl.
~~ -- ....--:-.;.o:-.::.:-;.:.·:.-.oo;.;:-::...·-::c::--:-:c.

i!. . -=-~-·::~.---------------------:)i"~"'= ,.""~':.:"--'-''~"'-''.''"--"--~il.=--'··- =, ..... tl

Figure 1. The new beam transport system in the RILAC facility is illustrated. The CSM consists of six boostercavities (Al~A6), a charge stripper and a &celerator (Dl). The beam transport system has one trunk linefrom the RILAC to the RRC and six branches for experiments. Four sets of quadrupole magnets (TQ 1~TQ4)
are newly fabricated.

The six branches (beam line el ~ e6) aim to provire
beams accelerated by the RILAC or the RILAC + CSM for
use in several experiments. We plan to use the e3 beam linefor the search for super-heavy elements, the e6 beam line for.
the accelerator mass spectrometer, and the e5 beam line todevelop a new charge stripper system, and the e4 beam line
is exclusively used by the CNS of Tokyo University.
The maximum beam energy is now 5.8 MeV/nucleon
whereas that of the RILAC is limited to be 4 MeV/nucleon.
It enables us to conduct the search for super-heavy elements
via a sub-barrier fusion reaction using a gas-filled recoil
isotope separator (GARIS) installed in the e3 beam line.
The maximum magnetic rigid.ty is limited to 2.1 Tm forthe beam lines e2 and e3 and 1.2 Tm for beam lines e4, e5
and e6. In contrast, the maximum magnetic rigidity of thebeams accelerated by the CSM is 4 Tm. Beam line e1
accepts all the beams because there is no insertion ofbending magnets.
The new beam transport system is mainly composed ofthe devices used in the old beam lines. What we have newly
constructed are three dipole magnets, four quadrupole
triplets, power supplies for the quadrupole magnets andseveral beam-monitoring revices. For the new dipole
magnets, we use existing power supplies. The
specifications of the dipole magnets are summarized inTable 1. We should mention that the tape coil technique isused for these magnets to reduce power consumption andspace. These dipole magnets were fabricated by TOKIN.
The construction of the new beam transport system has
finished last May.

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T~Ee

Deflection angle (deg.)Curvature radius (m)Maximum field (T)Pole gap (mm)Pole face rotation (deg.)
Total coil windings
Maximum current (A)Maximum voltage (V)

BM90
90
1.4
1.50
60
25/25
43220065

BM85sw243060
1.6 0.8
0.8
1.50
1.50
60
60
0/0 0/30 25/25
432432200200
3742Table 1 Specifications of newly constructed dipolemagnets.

The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

46BEAM DIAGNOSIS

A beam diagnosis cbvice for the CSM was cbveloped
Figure 1 and 2 show the diagnosis chamber and the cutting
view from the diagnosis chamber, respectively. The beamdiagnosis chamber was designed to be very compact because
the maximum space for the chamber was limited to 130mm. This diagnosis chamber contains the phase probe, theprofile monitor and the Faraday cup and also has the special
gate valve. This gate valves close the both beam entrances
to the vacuum chamber by one movement. Therefore, theprofile monitor and the Faraday cup can be maintained
without breaking the vacuum for the beam line. The phaseprobe is installed in the section of the short beam pipe
which connects the CSM cavity with the diagnosis
chamber. The phase probe has a ring electrocb with adiameter of 40 mm and a thickness of8 mm, and its signal
line exits the chamber through the vacuum-sealed SMA
connector whose ground side is floated.

0Phaseprobe

IOOmm

Figure 2. The cutting view from the diagnosis chamber.

5Because the maximum beam energy of the CSM isbeyond the Coulomb barrier, the local radiation shield isadcbd around the bending magnet BM90 and the GARIS
assuming a 10 p ,u A primary beam stops there.
The radiation safety control system of the RILAC
facility have been replaced with a new one, which consistsof a radiation monitoring system, an access control system
and a beam interlock system.

7BEAM ACCELERATION TEST

We started test operationsofthe CSM in May2001. We
accelerated Carbon and Argon beams using the CSM. For40Arbeams, weobtained5.8 MeV/nucleon with an intensityof 4.8 p ,u A The beam energy was retermined by theanalyzer magnet BM90 in which a NMR probe measured
magnetic flux rensity precisely. The maximum
transmission efficiency through the CSM is 98 % for anAr 11+ beam. The maximum transmission efficiency from theion soura: to the end of the CSM is however 62% in thiscase, because the typical transmission efficiency from theion source to the end of the RILAC is 50 to 70 %.
We have restarted beam services to the RRC experiments
without acceleration by the CSM. We also marepreliminary beam tests for the GARIS experiment. For
both cases, we did not detect sizable beam loss.

REFERENCES

cup

I..L.-I

RADIATION PROTECTION

WATERCOOLING SYSTEM

A new cbionizer watercooling system was installed inSeptember 2000. The cooling capacity is 1.3 MW. Thissystem has been used for the CSM, for four quadupole
triplet magnets of the CSM section and for the power
supplies of the quadupole triplet magnets. The total waterflow is 4300 !/min. The total water flow per cavity of theCSM is 600 1/min.

[l]M. Orera eta!.: "Variable Frequency Heavy-Ion Linac,
RILAC", Nucl. Instr. Meth., 227 187 (1984)
121E. Ike?.awa et a!.: "ECR Ion Source for RIKEN Heavy
IonLinac", The 8th Sympo. onAccel. Sci .. and Tech.,
Saitama, Japan (1991) 73[3]0. Kamigaito et a!.: "Recent Developments of theFolchl-Coaxial RFQ for the RIKEN Heavy-ion Linac",
Proceedings of the XIX International LINAC
Conference, Chicago, 1998, p.780.
[4]T. Nakagawa et al.: "RecentProgressofRIKEN 18 GHzECRIS", 1997 Particle Accelerator Conference, 1997,Vancouver (1997).
[51 Y. Yano eta!.: Proc. 1997 Particle Accelerator Conf.
(PAC97), Vancouver, Canada, May 1997, p.930(1997)[61 0. Kamigaito eta!.: Proc. 12th Symp. on Accelerator
Science and Technology, October 27-29, 1999, p. 233.
[71 0. Kamigaito et a!.: RIKEN Accel. Prog. Rep. 34,p322 (2001)[81 0. Kamigaito et a!.: "RF Cavities of the RIKEN
Charge-State Multiplier", in this Proceedings.

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