JAERI-Conf 95-021

3p1-2
RII<EN RI BEAM FACTORY PROJECT
Yasushige Y ANO, Akira GOTO, Takeshi KATAYAMA*, and RIBF GroupRIKEN Accelerator Research Facility (RARF)
RIKEN, Wako, Saitama 351-01, Japan*Institute for Nuclear Study, University of Tokyo,Tanashi, Tokyo 188, Japan

1. Introduction
The RARF proposes "RIKEN RI Beam Factory" as anext facility-expanding project. The factory takes theaim at providing RI (Radioactive Isotope) beams of thewhole mass range with the world-highest intensities in awide energy range up to several hundreds MeV/nucleon.
This paper describes a conceptual design of anaccelerator complex most suitable for realizing thefactory, and briefly presents Multi-USe Experimental
Storage rings (MUSES) proposed as a new type ofexperimental facility.
2. Accelerator Complex Proposed for
RIKEN RI Beam Factory
The best means to generate such RI beams is theutilization of the so-called "projectile fragmentation." Ingeneral, the reaction cross section for this projectile
fragmentation steeply enhances with increasing anenergy of a primary beam up to 100 MeV/nuclcon, andit saturates above around this energy. Thus, in order toefficiently generate RI beams of the whole mass range
using this method, firstly, primary-beam energies are
required to exceed at least 100 MeV/nucleon even forvery heavy ions such as uranium. Due to this condition,
the availability of RI beams at the present RARF isrestricted to their mass less than around 60. Secondly,
needless to say, intensities of primary beams must be as
high as possible. Thirdly, from the cost-effectiveness

AI LAC
FCRFQ
f=18-38MHz f=18-38MHz[constr.][existing]point of view, the existing machines should be exploitedand utilized as much as possible. Based upon these
considerations, we propose an accelerator complex as
illustrated in Fig. 1 which possesses such acceleration
performance that a 100-MeV!nucleon uranium beamwith the intensity over 1 ppA is obtainable.
A new injector!) composed of a frequency-tunable
folded-coaxial RFQ linac (FCRFQ)2) equipped with an
18-GHz ECR ion source (ECRIS-18)3) is underconstruction in order to greatly upgrade the RILAC
performance especially in the beam intensity. We use
this machine as the initial-stage of the accelerator
complex.
A high-intensity heavy-ion d.c. beam produced by
the ECRIS-18 is bunched and accelerated by theFCRFQ with the transmission efficiency of as high as
85% even at 1 rnA. The value of the efficiency wascalculated by the computer code BEAMPATH.4) This
pre-accelerated beam is fully accepted and accelerated
by the existing RILAC.
The output beam from the RILAC is passed througha charge-state multiplier (CSM, under design) to reduce
its magnetic rigidity with the velocity unchanged, andinjected into the existing RRC. The CSM consists of anaccelerator, a charge stripper and a decelerator. Theaccelerator and decelerator are of frequency-tunable IH
linacs, whose operational radio-frequencies are twicethat of the RILAC to double an acceleration gradient. In
the present design a maximum gap voltage is set to be
350 kV, and total lengths of these linacs are 12.4 meters

CSM
f=36-76MHz[design]ARC
f=18-38MHz
h=9[existing]SAC
f=18-38MHz
h=6[design]Fig. 1. Schematic diagram of the Heavy-ion Accelerator Complex
proposed for the RIKEN RI Beam Factory.

-457-JAERI-Conf 95-021(the partition into three or four units are necessary) and5.5 meters, respectively. Transmission efficiency
through the CSM depends only on charge state
distributions behind the charge stripper foil because the6-dimensional emittance of the RILAC beam is alreadyadiabatically damped so as to be fully captured by theacceptance of the CSM linacs. We estimate the yield ofa given charge state in terms of Shima's formula4)
which is reliable in the relevant energy region. The
CSM is a decisive device to obtain a higher-intensity or
higher-energy very-heavy-ion beam in the proposed
accelerator scheme; with this device the magnetic
rigidity of a most-probable charge-state beam can be
decreased down to the acceptable value of the RRC evenwhen the injection velocity into the RRC is increased.
Velocity of the RRC output beam is amplified by afactor of 2.26 with a six-sector superconducting ring
cyclotron (SRC, under design)6), 7), when the mean
extraction radius (5.70 m) of the SRC is taken to be 2.26
times the mean injection radius (2.37 m). This mean
injection radius is 2/3 times the mean extraction radiusof the RRC. To meet a good matching condition, theharmonic number in the SRC is taken to be 6 as that in
the RRC is 9. The preliminary calculation of betatronfrequency excursions implies that when we set the sector
angle to be 23.5 degrees the maximum attainable energy
is limited to be around 400 MeV /nucleon to avoid thecrossing overvz=l.O resonance.6)
Here, we illustrate the acceleration of a uranium-ion
beam up to 100 MeV/nucleon. The rf frequency of theRILAC is 23.0 MHz. A 238u16+ beam with an intensity(IECR) of 145 e~ from the ECRIS-18 (this intensity isextrapolated from the 10 GHz CAPRICE data) isaccelerated by the RILAC-CSM to 1.07 MeV/nucleon(ERILAC). In the CSM the charge state is increased
from 16+ (qECR) to 49+ (qCSM) by the stripping at
2.48 MeV/nucleon. The yield of 49+ and thetransmission efficiency of the FCRFQ are estimated tobe 0.17 and 0.85, respectively, and thus a beam intensityof 1.3 pJlA is to be obtained. This beam intensity (ISRC)
is preserved up to the final energy, provided that thetransmission efficiency of both of the RRC and the SRC
is 100% (this can be achieved by the off-centering
acceleration technique which is routinely used for theRRC). The RRC output energy (ERRC) is 17.5
MeV/nucleon, and the SRC final energy (ESCR) is 100
MeV/nucleon. The SRC sector field at the extraction(BSRC) is needed to reach to 3.9 T. Similarly, themaximum beam intensities for typical gaseous elements
are obtained as listed in Table 1, provided that the sector
field (BSRC) of 4T at the maximum can be achieved.
Quite high beam intensities can be provided
especially for light ions, but use of such primary beams
is not realistic from a viewpoint of the radiationshielding-problem. We consider that a primary-beam
intensity of 1pJlA is sufficient to generate RI beams withdesirable intensities in the whole mass region: These
primary beams will give us possibility to create andidentify as many as one thousand kinds of new isotopes.

Table 1. Prospects of primary-beam intensities of typical heavy ions.
lon

160 840Ar 1784Kr30
129x9 38
238u85
238u58238u49RF frq
MHz

38.1
37.0
34.930.330.3
27.2
23.0

qCSM

ERRC
MeV/uESRC
MeV/uJSRCe~ERILAC
MeV/up~8 SRC
tesla

800
750
200
140
2780
145

2.94
2.. 77
2.46
1.85
1.85
1.. 49
1.07

817
30
38
59
58
49

50.5
47.4
41.8
31.0
31.0
24.7
17.5

400
364
300
200
200
150
100

113
34
3.4
1.4
0.04*
0.22
1.3

3.4
3.8
4.0
3.9
3.2
4.0
3.9

qECR

1ECR

6814
15
282216* The charge-stripping is done in between the RRC and the SRC. The yield is assumed to be 30%.
3. Multi-Use Experimental Storage Rings(MUSES)
Figure 2 displays a quite preliminary lay out of theRI beam factory. The MUSES, installed downstream of
an RI-beam generator (Big RIPS) for the SRC, consistsof Double Storage Rings (DSR) and a small-sized
Accumulator-Cooler Ring (ACR). The DSR permits
various types of unique colliding experiments: ion-ion
merging or head-on collisions; collisions of electron andion (stable or RI) beams; internal target experiments;
and atomic and molecular physics with cooling electronbeams. On the other hand, the ACR functions
exclusively for the accumulation and cooling of RI
beams by the multi-tum injection plus RF-stacking
associated with the electron cooling as well as for theacceleration of electron beams from 0.5 GeV up to 2.5
Ge V and their radiation damping: i.e., RI or electron
beams are improved in quality by the ACR, and areinjected into the DSR by one turn. With the ACR, theacceptance required for the DSR is significantly-458-

JAERI-Conf 95-021

reduced. In the figure, the schematic drawing of theDSR is shown, but that of the ACR are not given.
In the DSR two rings of the same specifications asshown in Table 2 are vertically stacked. Each lattice
structure takes the form of a racetrack to accommodate
two long straight sections. These straight sections of one
ring vertically intersect those of the other ring at twocolliding points. The ring circumference is 202.08 m,
which is 6 .times the extraction circumference of theSRC. The maximum Bp-value becomes 12.76 Tm whena dipole field strength is 1.5 Tat the maximum. If highenergy ion beams are demanded, the DSR serves as anion synchrotron as well. The maximum energy is given,for example, to be 3.0 GeV for protons; 1.2
GeV/nucleon for light ions of q/A=0.5; and 0.82
GeV/nucleon for u92+ ions. For electrons the ACR
boosts them up to the maximum energy of 2.5 GeV, andthese electrons are stored in the DSR. In the present
lattice structure, the betatron tune values are 6.335(horizontal) and 5.763 (vertical). The operating ionbeam energy is kept to be under the transition energy,
since the transition gamma is as high as 4.86. At thecolliding points the beta-function amplitudes are 0.6 mfor both directions. The field-free section near thecolliding points where experimental detector systems areinstalled is 16.7 m in length. These two long straightsections are dispersion-free in horizontal and verticaldirections.
One of the key researches planned in the DSR is thecolliding experiment of an electron beam with an RI
beam: 2.5 GeV electrons accumulated in one ring of theDSR are collided with an RI beam stored in the otherring. At 2.5 GeV, the de-Broglie wave-length of theelectrons in the rest frame of the RI beam becomes 0.2fm, which is sufficiently short to study the nuclearstructure. To keep a sufficiently long Toushek lifetime,
the RF voltage of 2.0 MV is applied to the electron
beam. The number of stored electrons amounts up to
1.9x 1 0 12 particles which is limited due to thelongitudinal coupled bunch instability. The typicalcolliding luminosity for the electrons and RI ions isestimated to be 5.6xto26tcm2/s, provided that lx107
particles of RI ions are stored and synchronously
collided with electron bunches.
Other experiments such as ion-ion merging
collisions at small angles are also envisaged. Theluminosity is expected to be around lxlo26tcm2/s when
the number of stored ions are assumed at the spacecharge limit of 4x1o12 particles and the colliding angle
is 10 degrees.
For internal target experiments in the DSR, thestochastic cooling method is used. The band width isconservatively assumed at 500 MHz, and the feedback
gain is 130 dB which is limited by an available widebandRFpowerof lOOkW.
Various aspects of beam-dynamic problems related
to the detailed design of the DSR is being studied (one ofthem is given in Ref. 8), and the optimization ofparameters of the ACR is under way.
Table 2. Parameters of the DSR.
Circumference C (m)Max.Bp (Tm)
Average Radius R (m)Radius of Curvature p (m)Max. Beam Energy
proton (GeV)
ion (q!A = 0.5) (GeV/nucleon)ion (q!A = 0.387) (GeV/nucleon)
electron (GeV)
Betatron Tune Values (Q:x!Qy)
Momentum Compaction
Transition y
Max. Betatron Amplitude <Pxl/3y, m)Max. Dispersion Function (Dx!Dy. m)
Betatron Amplitude
at Interaction Point <Px*l/3y*. m)
Length of Field-free Section
at Colliding Section (m)202.078
12.76
32.178
8.506
3.00
1.20
0.82
6.350/5.763
0.04244.859
22.0/13.5
3.023/0.666
0.600/0.600
16.708RI Beam Factory
Fig. 2. Preliminary lay out of the RI beam factory.
References
1) A. Goto et al., in this proceedings.
2) 0. Kamigaito et al., in this proceedings.
3) T. Nakagawa et al., in this proceedings.
4) K. Shima et al.: Atomic Data and Nuclear Data
Tables, 51, 174 1992
5) Y. Batygin et al., in this proceedings.
6) T. Mitsumoto et al., in this proceedings.
7) T. Kawaguchi et al., in this proceedings.
8) Y. Batygin et al., in this proceedings. ·-459-