Th;e 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

RIKEN RI-Beam Factory Project
Yasushige YANO, Akira GOTO and Takeshi KATAYAMA*RII<EN,Wako Saitama 351-01, JAPAN*Center for Nuclear Study, School of Science, University of Tokyo,
Tanashi, Tokyo 188, JAPAN

Abstract
The "RI-Beam Factory" project has been proposed forupgrading the RIKEN Accelerator Research Facility. In
1997 fiscal year, the construction budget for the first phaseof this project has been approved. In the factory a cascade ofa K930-MeV ring cyclotron and a K2500-MeV superconducting ring cyclotron will be construe~ as an energy
booster of the existing ring cyclotron. The final energy will
be increased up to more than 100 MeV/nucleon. even forvery heavy ions. By the projectile fragmentation these energetic heavy-ion beams will be converted into RI (radioisotope) beams covering over the whole range of atomic
masses and with energies of several hundreds MeV/nucleon.
Moreover, this factory will include a next generation of themulti-use experimental storage rings (MUSES) consistingof an accumulator-cooler ring, a booster synchrotron ringand double storage rings. The MUSES will enable us toconduct various types of unique colliding experiments.

1 Introduction
The RARF (RIKEN Accelerator Research Facility) hasa heavy-ion accelerator complex consisting of a K540-MeVring cyclotron (RRC) as a main accelerator and two different
types of injectors: a frequency-variable Wideroe linac(RILAC) and a K70-MeV AVF cyclotron (AVF). The facility provides heavy-ion (HI) beams over the whole atomic
mass range and in a wide energy range from 0.6 MeV/nu-cleon to 135 MeV/nucleon. One of the remarkable featuresof this facility is capability of supplying light-atomic-mass
RI (radioisotope) beams with the world-highest level of intensity which are produced by means of the projectile fragment separator, RIPS [1].
In order to further promote experimental programs utilizing RI beams, the RARF undertakes the construction of"RI Beam Factory". The bird's eye view of its layout isillustrated in Fig. 1. The factory is aimed at providing RI
beams covering over the whole atomic-mass range with very
high intensity in a wide energy range up to several hundreds
MeV/nucleon.

2 The Heavy-ion Accelerator Complex for Highintensity RI Beam Generation
The factory utilizes the "projectile fragmentation" togenerate RI beams of intermediate energies. To enable theefficient generation of such RI beams covering the wholeatomic masses, are needed high-intensity primary heavyions, up to uranium ions, with the energies exceeding 100
MeV/nucleon. In order to realize those energies, a cascade of
an intermediate-stage ring cyclotron (ffiC) with K=930 MeV
and a superconducting ring cyclotron (SRC) with K=2500
MeV will be constructed as an energy booster of the existing RRC. In addition, to realize enough intensity, we will
upgrade the RILAC which serves as the initial-stage accelerator by introducing a new pre-injector and a charge-state
multiplier (CSM). This accelerator complex will possess
BSR: Booster Synchrotron Ring with a0.3 GeV electron linac to accelerate anRl (HI) or an electron beam

Existing Facility

DSR: Double Storage Rings forcolliding experiments of HI, Rl,· photon, and electron beams

050m

IRC, SRC: A cascade of Ring Cyclotrons(RC's) to boost the energy of HI beams
from the RRC

ACR:.Accumulator Cooler Ring to coolan Rl (HI) beam using stochastic cooling
and/or electron cooling method

Fig. 1 Bird's eye view of "RI-Beam Factory" layout.

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such performance that a 100 MeV/nucleon uranium beamwith the intensity over 1 pJ.!A is obtainable.
2.1 Pre-injector for R1LAC

In order to upgrade the RILAC performance in thebeam intensity by one or two orders of magnitude, its new· pre-injector system consisting of a frequency-tunable foldedcoaxial RFQ linac (FC-RFQ) equipped with an 18-GHz
ECR ion source (ECRIS-18) has been developed. In therecent acceleration tests, the FC-RFQ has successfully covered HI beams in the energy-mass region required, and thebeam transmission efficiency of about 90 % at the maximum was obtained. In addition, high-intensity highlycharged ion beams have been produced by the ECRIS-18.

The MUSES (Multi-USe Experimental Storage rings)
consists of an Accumulator-Cooler Ring (ACR), a Booster
Synchrotron Ring (BSR) with an injector electron linac andDouble Storage Rings (DSR). It will be installed downstream from the SRC and an RI beam separator, Big-RIPS.
The ACR functions for accumulation and cooling ofRI (HI) beams, and is also used for atomic and molecularphysics experiments with a cooler electron beam. The BSR
works solely for the acceleration of RI (HI) and electronbeams. The DSR permits various types of unique colliding
experiments: RI (HI) - HI merging or head-on collisions;collisions between electron and RI (HI) beams; and collisions of RI (HI) beams with a high brilliant X-ray emitted
from an undulator which is inserted in one ring of the DSR.
The details of the MUSES appears in the papers inthis proceedings.

2.2 CSM
3.1 Production of RI Beams

The CSM consists of an accelerator, a charge stripper
and a decelerator. Its functions are to produce higher charge
state of ion beams by further increasing the stripping energy
and to reduce their magnetic rigidity by decelerating them tothe initial energy. With this device the magnetic rigidity of
the RILAC beam with a most-probable charge state can be
reduced to the acceptable value of the RRC even when theinjection velocity into the RRC is increased. The accelerator
and decelerator are of a type of frequency-tunable IH linac
whose operational radio-frequencies are twice as that of theRILAC to double an acceleration gradient.
2.3 IRC-SRC

The IRC's maximum energies are 127 MeV/nucleon
for light ions up to around Ar, 102 MeV/nucleon for
Kr30+, and 58 MeV/nucleon for u58+. The minimum energy is 25 .MeV/nucleon. In the SRC the maximum energies are increased to 400 MeV/nucleon for light ions up toaround Ar, to 300 MeV/nucleon for Kr30+, to 150 MeV/nucleon for u58+ and to 100 MeV/nucleon for u49+. The
minimum energy is 60 MeV/nucleon.
In this two-stage cyclotron scheme the simultaneous
utilization of the HI beams is possible in both of the existing experimental facility and the new facility, when part of
the IRC beam is charge-stripped and is transferred back to
the existing facility.
We have undertaken the fabrication of a full-scalemodel sector magnet of the SRC without a yoke to verify
the mechanical and cryogenic design. The superconductors
for the main and trim coils have already been complete. Thistask is scheduled to be finished by the spring of 1998.
The details of the IRC-SRC system is described in ref.
[2].
3The SRC's HI beams irradiate a production target andare converted into RI beams through the projectile fragmentation. RI beams generated are the mixture of various RI's;
and therefore, they will be purified by means of momentum
and charge-state selection at Big-RIPS.
Figure 2 shows the time structure of the SRC's beam
which will be produced by the future pre-injector of theRILAC. The structure consists of a series of a short pulse(SP) with high peak current (100 pJ.!A at the maximum) anda long pulse (LP) with low peak current (1 pJ.!A at themaximum). These pulses are split by the pulse magnet system of the Big-RIPS; and the RI beam generated by the SP
primary beam is transferred to the ACR, and those by theLP are transferred to the first-phase experimental hall.
The SP RI beam is transported to the injection pointof the ACR along the length of 70 m. At the end point oftransport line, a debuncher system will be installed to reducethe momentum spread of this beam.
3.2 Accumulation and Cooling of RI beams in ACR

RI-beam SP bunches corning from the Big-RIPS are
injected into the ACR by means of the multi-turn injection.
Short Pulse(100 PJ..lA max.)I~
to Exp. HallMulti-Use Experimental Storage Rings(MUSES)t
Fig. 2 Time structure of SRC's beam.

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The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Then the rf-stacking associated ·with the beam cooling is
performed. Momentum cooling continuously works during
the rf-stacking. This process is repeated at intervals of the rfstacking time of 30 ms plus the cooling time depending on
the RI-beam property.
Simulation study for both· of the electron cooling arxl
the stochastic cooling of RI beams was done. As a result, it
turned out that the stochastic cooling is much faster than theelectron cooling. This is due to the property of the RI beam:
the intensity is rather weak; and both of the momentum andemittance spreads are large.
The· RI beam accumulated in the ACR decays with its
own intrinsic life time. The number of the RI ions stored inthe ACR after the period of life time is determined by thebalance of the supply rate and the decay rate. The spacecharge limit was also considered in the estimation of themaximum number of RI ions stored in the ACR. Thislimit, however, becomes effective only for RI ions neighboring on the stability line with high production rate.
The accumulated RI beams in the ACR will be fast extracted and one-turn injected into the BSR.

3.3 BSRIn the BSR, RI (HI) beams will be accelerated to theenergy required for the experiment within 0.3 s, and thenwill be one-turn injected into the one ring of the DSR. Themaximum energies are: e.g., 1 GeV/nucleon for 238u92+,
1.5 GeV/nucleon for ions of charge-to-mass ratio (q/A) of112 and 3.5 GeV for protons. The slow-extraction channel
will also be prepared.
Electrons are accelerated up to 300 MeV by an electron
linac and then injected to the BSR. The BSR boosts theelectron energy up to 2.5 GeV at the maximum and supply
them to the one ring of the DSR. The expected beam current
in the DSR is about 500 rnA.
Figure 3 shows the HI-beam acceleration performanceby the RRC, ISR, SRC and BSR with expected beam in-tensity.

3.4 DSRThe DSR consists of vertically-stacked two rings ofthe similar specification. Each lattice structure takes theform of a racetrack to accommodate two long straight sections. These straight sections of one ring vertically intersect
those of the other ring at two colliding points: one point isused for the collision between an RI beam and an electron
beam at a collision angle of 20 mrad and the other for themerging of RI (HI) beams at a merging angle of 170 mrad.
RF cavities and beam injection devices are placed at theselong straight sections. Two short straight sections will beused for electron coolers to suppress the beam instabilities
and to make a short-bunch ion beams.
The ring circumference is 269.6 m. The maximum energies of the stored beams are 1.0 GeV/nucleon for u92+

1.4
1.2~

c::1.0~gc:: 0.8>
Q)~ 0.6e>3j 0.4
0.2
0.1
0.0
40

80

120
160
Atomic Mass

200240Fig. 3 Acceleration performance of HI beams ofRRC, IRC, SRC, and BSR.
ions, 1.5 GeV/nucleon for light ions of q/A=l/2, and 3.5
GeV for protons.
One of typical experiments conducted at the DSR isthe collision of an RI beam with an electron beam to precisely measure charge-density distribution of unstable nuclei. In the experiment, one ring of the DSR will be filledwith a high-current electron beam of nearly 500 rnA withthe energy of up to 2.5 GeV. The lattice of this electron
ring is designed so that the emittance of electron beam· is
10-6 1t m·rad from the point of view of the luminosity arxl
beam-beam effect. The parameters of the ion ring are different from those of the electron ring because of the difference
between lattices of the colliding section in two rings. Another usage of an electron beam is to generate high brilliant
X-ray by an undulator inserted in the electron ring. This Xray will shine Li-like RI ions circulating in the other ring.
By detecting fluorescence emission from the ions, new spectroscopy of unstable nuclei will be possible. For this purpose the electron-beam emittance is required to be as small
as 10-8 1t m·rad. This is achieved by forming the Double
Bend Achromatic (DBA) system in the arc.

4Construction Schedule

In the present schedule, the IRC, the SRC, the BigRIPS and the experimental installation will be completed in
2002. The construction of the MUSES is planned to start in2003 and to be fully finished in 2009.

REFERENCES[1] T. Kubo et al., Nucl. lnstrum. Meth., B70 (1992) 309.

[2] A. Goto et al.: in this proceedings.

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