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

PROGRESS REPORT OF RIKEN RI BEAM FACTORY
Y. Yano, A. Goto, M. Kase, T. Katayama, RUffiN, Wako-shi, Saitama 351-0198, Japan

Abstract
The first phase of the RUffiN radioisotope (RI) beamfactory project is under construction. A new cyclotron
cascade consisting of three ring cyclotrons with K=510
MeV, 980 MeV and 2500 MeV in each will becommissioned in 2005. It will boost the heavy-ion
beams' energies obtained by the existing K540-MeV ring
cyclotron up to 350 MeV/nucleon. Intense RI beams areproduced mostly via the projectile fragmentation of theseenergetic heavy ions or partially via in-flight fission of
uranium ions. In the second phase, various experimental
installations for direct use of these RI beams, anaccumulator cooler ring and an electron-RI beam collider,etc. will be built step by step.

1 INTRODUCTI ON
The RII<EN Accelerator Research Facility (RARF) iscurrently constructing the radioisotope (RI) beam factory(RIBF) which aims at a next generation facility capable ofproviding the world's most intense RI beams over thewhole range of atomic masses.
Figure 1 shows the plan view of the RIBF. At present
the RARF has the heavy-ion accelerator complex
consisting of a K540-MeV ring cyclotron (RRC) and two
different types of the injectors: a variable-frequency
Wideroe linac (RILAC) and a K70-MeV AVF cyclotron(A VF). Moreover, its projectile-fragment separator (RIPS)
has been providing the world's most intense light-atomicmass RI beams. In the new factory, a cascade of a KSl 0MeV fixed-frequency ring cyclotron (fRC), a K980-MeV
intermediate-stage ring cyclotron (IRC) and a K2500-MeV
superconducting ring cyclotron (SRC) will be a postaccelerator for the existing RRC. This new cyclotron
system will be able to boost the RRC beam's output
energy up to 400 MeV/nucleon for light ions and 350
MeV/nucleon for very heavy ions. The goal of the beam
intensity is higher than lpJ.lA.
As in the existing RIPS, RI beams will be generated
mostly by projectile fragmentation. In addition, in-flightfission of uranium ions will be used for the efficient
production of very neutron-rich isotopes in the medium
mass region. A BigRIPS will be installed to generatesuch RI beams with larger magnetic rigidity.
The RIBF will include an electron-RI beam collider (eRI Collider) equipped wth an accumulator cooler ring(ACR) for conducting electron scattering experiments on
unstable nuclei.

2 RILAC
Figure 2 illustrates the schematic diagram of the heavyion accelerator complex for the RIBF. The RILAC will be
the initial-stage accelerator for the RIBF accelerator
complex. In order to upgrade the RILAC performance inthe beam intensity, the pre-injector system consisting of afrequency-tunable folded-coaxial RFQ linac (FC-RFQ)
equipped with an 18-GHz ECR ion source (ECRIS-18)-

has been developed. The FC-RFQ has successfully
covered heavy-ion beams in the energy-mass region
required, and the beam transmission efficiency of about 90% is routinely obtained. In addition, high-intensity
highly-charged ion beams have been produced by the
ECRIS-18.
Recently, the charge-state multiplier (CSM) has been
partially completed. It consists of two variable-frequency
accelerator linacs, four fixed-frequency accelerator linacs,
and one variable-frequency decelerator linac. With thisCSM, very intense heavy-ion beams with 5.85 MeV/
nucleon at maximum will be available in the RILAC
experimental hall especially for the super-heavy element
search. In addition, the acceleration performance of the
RILAC-RRC system will be greatly upgraded.

3 NEW CYCLOTRON CASCADEAs shown in Fig. 2, the velocity gains in the fRC, theIRC and the SRC are 2.0, 1.5 and 1.506, respectively.
Figure 3 shows the energies at each acceleration stage forthe ion mass. When bypassing the fRC, the combinationof the IRC and the SRC accelerates light ions reachingaround Ar up to 400 MeV/nucleon, Kr0+ up to 300
MeV/nucleon, U58+ up to 150 MeV/nucleon and U49 + up
to 100 MeV/nucleon. The beam intensity is expected tobe 1 pJ.lA for light ions, but to be less than 1 pJ.lA forvery heavy ions. With the fRC, which is a fixed rffrequency machine to minimize the construction cost,very heavy ions from Kr to U can be accelerated up to 350
MeV/nucleon with high intensities (the goal is 1 pJ.lA),
because the low-frequency operation of the RILAC allows
us to take full advantage of high-intensity, low-chargestate ions from the ion source. As shown in Fig. 2, forexample, U 10+ ions are accelerated by the RILAC, thencharge-stripped U 35+ through the RRC, U72+ through thefRC, and U 88+ through the IRC and the SRC. Only 1% of
U 10+ ions from the ECRIS are accelerated to the final
energy due to the charge stripping loss. In order to skip
over a nasty low-energy-stage charge stripping to realize a
350-MeV/nucleon uranium beam with 1 pJ.lA, we have todevelop a powerful ECRIS that is able to produce U35+
beam with 15 pJ.lA. For Xe ions, our ECRIS-18 presently
produces Xe20+ beam with 10 pJ.lA to realize a 350
MeV/nucleon Xe beam with 1.8 pJ.lA without the charge
stripping at the low energy as shown in Fig. 2.
The IRC, the plan view of which is shown in Fig. 4,
is a four-sector room-temperature ring cyclotron, which isdesigned so as to be imitative of the RRC to facilitate its
fabrication. The maximum sector field is 1.9 T
corresponding to a magnetic rigidity of 4.57 Tm. The
mean extraction radius is 4.15 m and the harmonic
number is 7. The rf frequency is ranged from 18 to 38
MHz. The IRC has been completed in the factory and themagnetic field is being mapped.
The SRC, the plan view of which is shown in Fig. 5,
is a six-sector superconducting ring cyclotron. The

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

ion-Ring
e-AingInternal
Target

inac

ACR
RF

EB-Cooler

RIB Experimental Room==~Phase II
Phase I

RILAC
CSM
Existing Facility:
RILAC: Frequency-variable Heavy-ion Linac,
CSM: Charge State Multiplier,
RRC: K540MeV Ring Cyclotron,
AVF: K70MeV AVF Cyclotron,
RIPS: Projectile Fragment Separator.
RIBF Phase 1:
SRC: K2500MeV Superconducting Ring Cyclotron,
IRC: K980MeV Ring Cyclotron,fRC: K520MeV Fixed-frequency Ring Cyclotron,
BigRIPS: Projectile Fragment Separator.
RIBF Phase II:
ACR: Accumulator Cooler Ring,
e-RI Collider: Electron-RI Beam Collider.

Figure 1: The layout of the RI Beam Factory (RIB F). The first phase of the RIBF building is presently underconstruction and will be completed in 2003. The construction of the second-phase building, the layout of
which is preliminarily depicted here, is planned to begin in 2002 and will be completed in 2005.
maximum magnetic rigidity of extracted beams is 8 Tm
which exceeds that of 350 MeV/nucleon U88+ beam (7.94
Tm). The mean extraction radius is 5.36 m and theharmonic number is 6.

As shown in Fig. 5, the SRC is almost completely
covered with soft-iron slabs about 0.8 m in thickness,
except in the central region. A part of these iron slabs arebridged on the top and bottom of the valley regions- 21-

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

RILAC

K(MeV)= 540

510

980

2500

RRC

fRC

IRC

SRC

18-38 MHz(36.66 MHz)

18-38 MHZ

18-38 MHZ

2.0
8

1.5
7

1.506

CSM
Stripper1

FCRFQ
18GHz
ECRIS

18-38 MHZ

18-38 MHZ

36-76 MHz~out1~in= 4 _0

h=918.88 MHZ

18.33 MHZ

Xe q=20+
u q=10+36.66 MHz

( -)
(1/6)

18.33 MHz

115

46

11

E(MeV/nucleon) = 0.7 0.9 0.7

36.66 MHZ

6

36.66 MHZ

20+ (0.3) 48+ (0.6)
35+ (1/5) 72+ (1/3)

51+
88+

350
36.66 MHZ

51+
88+

Figure 2: Schematic diagram of the RIBF accelerator complex, showing charge states and yields in eachacceleration stage for obtaining a 350 MeV/nucleon Xe/U beam. The numbers in the parentheses give
yield ratios for the repective charge states after each stripper..
between the sector magnets. The other part of them are stored energy are about 4 MAlsector and 235 MJ,
placed vertically between these top and bottom slabs so as respectively. All the injection and extraction magnetic
to cover the space between the back yokes of the channels inside the sector magnets are normal with theneighboring sector magnets. The total weight of this moderate power consumption and their structures are very
falling-U-shaped iron-slab structure (referred to as the similar to those for the RRC and the IRC. The shift of"iron cover") is about 4,000 tons (the total weight of the the injection and extraction trajectory depending on the
SRC amounts to 7,800 tons). The verticaloutside slabs are assembled to form a doubleleafed hinged door to be opened when themaintenance is carried out for the rf resonators,
400
vacuum pumps, and so on in the valley region.
This "iron cover" yields the following good c:
results: (1) The SRC is self radiation-shielding. o
We need neither very thick concrete-shielding ~ 300
walls nor huge non-magnetic local shielding. (2) ::.:::1
The SRC is self leakage-flux-shielding (the stray ~field even in the valley is as low as 0.1 T at <D
maximum.) We need neither the active magnetic :::\Eshielding which is difficult to fabricate nor the - 200
thick iron plates enclosing the huge SRC vault. >The small stray field in the valley allows us to e>Q)
use cryopumps, motors, control devices, and so c:
on in a safe situation. The stray field outside the w 100
SRC is about 200 gauss at the maximum near
the yoke and the vertical outside shield-wall. We
place the rf oscillators near the SRC as they arefor the RRC and the IRC. The SRC vault is0very safe for those working at the site even inside
the cyclotron.
120 160 200 240
8040
1
The sector field needed to bend, for example,
U58+ 150 MeV/nucleon (7.52 Tm) is 3.7 T.
Atomic Mass
According to relatively low flutter, the operating
domain of the vertical betatron frequencies locate
Figure 3: Energy vs. mass performance of RIBF accelerator
in the values between 0.5-1.0. The maximum
complex.
magneto-motive force required and the maximum- 22-

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

Figure 4: Plan view of the IRC.
negative stray field strength is very small (almost no
shift).
The winding of the main coil is scheduled to startaround September 2001. The completion of the SRC isscheduled for the spring of 2003.
The fRC is a four-sector room-temperature ring
cyclotron. The maximum magnetic _rigidity of extracted
beams is 3.28 Tm. The mean extraction radius is 2.77 m
and the harmonic number is 8. The rf frequency is fixed to
be 36.7 MHz. The detailed design is being made.

4 BIG RIPS
We will install a couple of RI-beam generators as
illustrated in Fig 1: the large-acceptance BigRIPS-L andthe small-acceptance BigRIPS-S. Both of them are
simultaneously utilized by time-sharing a primary beam.
The BigRIPS-L consists of a couple of achromatic
spectrometers connected to each other in series. The firststage spectrometer is used as a projectile fragment
separator to produce RI beams, while the second one isused as a spectrometer to make particle identification of
RI beams as well as to measure their momentum andangular dispersion. RI beams are tagged event by eventwith respect to momentum, angle and ion species. The
reason why we adopt this tandem scheme is that purity of
RI beams obtained by the first-stage is expected to be stillpoor due to the nature of energy loss in our energy
domain. RI beams tagged are transported to various
experimental set-ups placed downstream.
The BigRIPS-L is designed to have large acceptance, sothat it can efficiently collect projectile fragments pr<Xluced
by in-flight fission of uranium beams. This in-flightfission has high capability of producing very neutron-richmedium-heavy RI beams, because it has large production
cross-section for those isotopes. The acceptance of
BigRIPS has been taken to be 80 - 100 mrad for angle
and 6 % for momentum. Such large acceptance allows us
to _collect almost 50 % of fragments produced by the inflight fission of uranium beams at 350 MeV/nucleon,

Figure 5: Plan view of the SRC.
when the symmetric fission fragments are selected. For
producing RI beam species in other region of nuclear
chart, such as proton-rich isotopes and lighter neutron-richisotopes, projectile fragmentation of suitable heavy ionsis to be used. In this case, the BigRIPS-L can collectalmost 100 % of fragments produced.
The first-stage of BigRIPS-L is a mirror-symmetricsystem with two dipole magnets. A wedge-shaped energy
degrader is placed at its intermediate focus to makeisotopic separation. The second-stage is a mirrorsymmetric achromatic system with four dipole magnets.
The use of four dipole magnets allows us to obtain higher
momentum resolution, which is required for the tagging
of RI beams. The maximum bending power of BigRIPSL is about 8 Tm, when its optics is tuned for the large
acceptance mode to collect fission fragments. On the other
hand, when the optics is tuned for smaller acceptance,
which is nearly a half of the large acceptance, the bending
power limit increases to 9.5 Tm, which corresponds tothat of isotopes with AIZ=3 and E=400 MeV/nucleon.
This mode is to be used for collecting relatively lightneutron-rich RI beams produced by - projectile
fragmentation. The quadrupole magnets of BigRIPS-L aresuperconducting, so that the high acceptance and the large
bending power such as 20 T/m with a warm bore of 24
em in diameter can be achieved. Its prototype has been
built recently and the design has been successfully
confirmed by the test.
Huge normal concrete slabs of 5000 tons in total
weight surrounds the production target area for safely
shielding fast neutrons produced by 350 MeV/nucleon
CW heavy-ion beams with 1pJ.lA.

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

cavity is installed to compensate radiation loss.
Circumference of the electron ring is 114 m and the
A RI beam produced is transported to the injection harmonics is 182.
point of the ACR along the length of nearly 70 m. On
The ion ring has maximum rigidity of 8 Tm, which is
the transport line, a debuncher system and a skew the same as that of the ACR. The lattice of the arc section
quadrupoles or solenoids system will be installed to has mirror symmetry to make dispersion suppression
enhance the injection efficiency of the RI beam into the easy. An electron cooler is located in a short straight
ACR by improving the matching of the six-dimensional section to compensate the emittance growth by beamemittance of the RI beam produced to the six-dimensional beam effect. An RF cavity is also located to keep bunch
acceptance of the ACR.
length. The circumference of the ion ring is 146 m which
In Fig. 1 the plan view of the ACR is shown. The is the same as that of the ACR and the harmonics is 30.
ACR has asymmetric lattice structure consisting of the
In the colliding section, where two rings intercept, aachromatic arc (left) and the semi-isochronous arc (right) lattice of each ring is designed so as to get highto efficiently cool the accumulated RI beams especially in luminosity. The~ values are determined to be 2 m for thethe cooling time[l]. Its circumference is 146 m and the electron beam in both of horizontal and vertical directions
harmonic number is 30. In this configuration, the ACR and 2 m for the ion beam. These large ~ values are
accepts 227-MeV/nucleon RI beams which are most required by obtaining better angular resolution for theefficiently produced by 350-MeV/nucleon primary beams. electron spectrometers rather than reducing the hour-glass
The maximum magnetic rigidity is 8.0 Tm, the effect. We adopt the head-on collision scheme to gethorizontal/vertical acceptances are 1251t/401t mm.mrad higher luminosity. In order to realize this scheme, theand the momentum acceptance is ±1 %. The isochronous- ratio of the magnetic rigidity of the RI beam to that ofmode operation is also possible when the precision mass electron beam is kept to be constant (2.9) bymeasurement is done.
appropriately selecting the electron beam's energy.
RI-beam' s micro-pulses coming from the BigRIPS are
The design mentioned above is preliminary. The
injected into the ACR by means of the multi-tum luminosity required is higher than 1027/cm 2/s in order toinjection. Then, the rf-stacking is immediately performed. clearly measure charge distributions in unstable nuclei in
After repeating the injection and the rf-stacking by 4 some-ten-day experiments. This luminosity should betimes, the beam is pre-cooled by means of the stochastic obtained by primary heavy-ion beams with peak currents
cooling. One cycle of injection, rf-stacking and cooling is of 1pJ..LA. This limitation for the peak current
isexpected to take typically 100 ms. This cycle is repeated attributed mainly to the transient beam loading rather thanin the intrinsic lifetime of the RI or until the space charge the space-charge effect in the ring cyclotrons. The design
limit is reached. Following this process the accumulated goal is to obtain the above luminosity for unstable nuclei
beam is finally cooled to less than 0.1% in momentum having their life time shorter than 1 minute. In the
spread and O.l1t mm.mrad in transeverse emittance by present design such level of the luminosity is attainable
combining the stochastic and the electron cooling for life times longer than 100 seconds, assuming that thetechniques.
tolerable linear tune shift,; is to be 0.05.
The number of RI ions stored in the ACR is determined
7 SCHEDULE
by the balance of the supply rate and decay rate due to theintrinsic lifetime. This is limited by space charge effect
The construction of the first-phase building, and therather than the lifetime for RI ions neighboring on the fabrication of the IRC, the SRC and the BigRIPS will bestability line, which has high production rate and long finished early in 2003. In 2003 and 2004, the overall
lifetime.
installation and final tuning of these machines will be
The accumulated RI beams in the ACR will be fast done. We will submit the budget for the fRC in FY2002,
extracted and one-tum injected into the e-RI collider.
and we expect to install this cyclotron during the above
final
tuning. The first RI beam from the BigRIPS is
6 E-RI COLLIDER
scheduled for the late autumn of 2005.
The e-RI collider for electron-scattering experiments on
The construction of the second-phase building will be
unstable nuclei consists of an electron and an ion storage started in 2002 and will be finished in 2005. After its
rings that intercept at one colliding point with each other.
completion, major experimental set-ups, e.g. a large
The electron-beam's energy is 500-700 MeV which is acceptance spectrometer and a gamma-ray detector, etc.,
obtained by an electron linac. This energy is determined the ACR system, and e-RI collider will be constructed andby experimental requirement for the resolution of electron- installed step by step.
scattering angles. The feasible stored-beam's current and
REFERENCES
the beam emittance are 500 rnA and 301t nm.rad,respectively to get high luminosity within the tolerable [1] M. Wakasugi et al.: Proc. of EPAC 2000, p.1357
beam-beam effect. The electron ring has a FODO structure (2000).
in arcs to realize the required emittance. A 500-MHz rf

5 ACR

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