The JAERI-KEK Joint RIB Project
Suehiro Takeuchi
Japan Atomic Energy Research Institute-Tokai Establishment
Shirakata-Shirane 2-4, Tokai, Naka, Ibaraki, Japan 319-1195
Abstract. The Japan Atomic Energy Research Institute (JAERI)-Tokai and the High Energy Physics Laboratory Institute of Particle and Nuclear Studies (KEK-IPNS) are developing an Isotope Separator On-Line (ISOL) type
radioactive-ion-beam (RIB) facility at the site of the JAERI tandem accelerator laboratory, as a joint project starting
from 2001. Proton beams from the tandem accelerator will be used to irradiate a uranium target close coupled to an ion
source will be used for producing RIBs. The RIBs will be accelerated by KEK linear accelerators (linacs), especially
built for this purpose. Acceleration will take place with a split-coaxial RFQ, followed by an inter-digital-H type linac
with exit beam energy of 1 MeV/u. Additional acceleration of beams to 2 MeV/u will be made by injecting into another
linac. These beams will be used for nuclear astrophysics research. In order to accelerate beams above the Coulomb
barrier for nuclear physics research, beams from these linacs can be further accelerated with the existing superconducting tandem-booster system.
accelerator. By use of proton beams from the 20 UR
Tandem accelerator at JAERI, the fission production
rate is expected to be as high as 1 × 109 /s in the
medium-heavy neutron-rich fission fragment mass
region. The joint RIB project officially began in 2001.
This paper describes the facility and reviews the
present status of the project and outlines plans for the
future.
INTRODUCTION
The Japan Atomic Energy Research Institute
(JAERI)-Tokai and the High Energy Physics
Laboratory-Institute of Particle and Nuclear Studies
(KEK-IPNS) have separately investigated construction
of ISOL type radioactive-ion-beam (RIB) facilities in
relation to two large proton accelerator projects.
JAERI proposed a 1.5 GeV intense proton linac
project for nuclear waste transmutation and neutron
science [1], while KEK proposed construction of the
Japan Hadron Facility (JHF) for use in various hadron
physics experiments, respectively, in the 1990s. The
two RIB proposals merged together as a natural
consequence of the consolidation of the two highintense high-energy proton accelerators in 1998 [2].
Moreover, the RIB project proceeded in the direction
of utilizing existing accelerators as a result of their
joint investigation (e.g., JAERI’s 20 UR tandem
accelerator and super-conducting (SC) booster and
KEK’s linac complex). The KEK linac system was
built at Tanashi (formerly the site of the Institute of
Nuclear Study (INS)) for accelerating RIBs before the
site was closed.
OVERVIEW OF THE RIB
ACCELERATION SYSTEM
The layout of the RIB acceleration system is shown in
Fig. 1. The JAERI tandem accelerator now assumes
the role of driver accelerator, delivering proton beams
or other heavy ion beams to RIB production targets.
The production target and close-coupled hightemperature RIB source are placed on an existing
ISOL platform located in the tandem laboratory. After
mass selection, singly-charged RIBs are injected into a
charge breeder increasing the charge-states of selected
heavy-ion beams as required for acceleration through
the whole linac complex without use of beam
intensity-loss, electron-stripping. The multiplycharged RIBs are transported through a low-energy
beam line to the RIB linac that consists of a splitcoaxial RFQ followed by an inter-digital-H type linac
A method for producing intense radioactive
isotopes (nearly enough for the generation of RIBs
without a high power driver) is available by utilizing
proton-induced fission products (FP) from uranium
targets using 30 MeV proton beams from the tandem
CP680, Application of Accelerators in Research and Industry: 17th Int'l. Conference, edited by J. L. Duggan and I. L. Morgan
© 2003 American Institute of Physics 0-7354-0149-7/03/$20.00
229
[3,4]. This system will deliver 1 MeV/u RIBs to the
experimental area.
boost capability will permit the study of RIB nuclear
physics. Stable ion beams can also be accelerated from
an ECR ion source in the new system. We expect a big
beam intensity increase compared to those presently
available with the present tandem plus booster system.
In the next stage, the energies of RIBs will be
boosted by the addition of another linac and by the
existing SC tandem booster. This additional energy
FIGURE 1.
laboratory.
Top view layout acceleration system for the joint JAERI-KEK RIB project in the JAERI tandem-booster
are also available. The machine operates reliably and
stably for more than 5,000 hours (230 days) per year.
The facility has eleven beam lines directed to research
stations. One of the lines passes straight through the
de-energized, bending magnet from which beams can
be injected into the SC tandem booster, as noted in
Fig. 1. Two beam lines are directed into the ISOL
target room. The next target room, which has been,
until recently used for fast-neutron scattering
experiments, will be used as the RIB accelerator and
experimental room for this project.
Tandem Accelerator
The JAERI tandem accelerator is a vertical folded
type 20 UR Pelletron (National Electrostatics
Corporation) that began operation in 1982. The
machine can deliver proton beams with beam energies
up to 36 MeV and intensities up to 3 µA, or heavy ion
beams with intensities up to 0.5 pµΑ [5]. In addition to
the normal operating mode of the tandem accelerator,
it is now equipped with a terminal mounted ECR ion
source [6], used to generate multiply charged ion
beams from gaseous feed materials, including noble
gas elements. In the single-end mode, 18 MeV protons
Aside from the RIB project, replacement of the 20
year old acceleration tubes for the tandem accelerator
is also scheduled as a renovation project. After
230
Ion sources
carrying out cleaning and de-gassing operations,
eighty new tubes, each with 21 ceramic gaps, will be
installed in place of the present 120 tubes, with 11
ceramic gaps. The cleaning of inside surfaces with
high pressure de-ionized water spray was recently
found by S. Takeuchi, et al to be a very effective way
to suppress discharges inside the tubes so that high
stability can be realized at a high operating voltages
without the long conditioning periods usually required
following new tube installation. The new tubes, in
combination with the newly developed cleaning
method will improve the beam energy performance of
the 20 UR tandem accelerator for conventional as well
as RIB driver applications.
The fissions products, so produced with our driver,
will be distributed over a 40 element range from Co to
Dy. The ionization efficiencies of the isotopes of these
elements depend on their physical and chemical
properties. Therefore, several types of ion sources will
be required for their processing. The ion sources that
we are presently being developed, include: a positive
surface ionization source and a low-voltage arcdischarge type ion source, developed by by S.
Ichikawa, et al [8]. The latter source is a modified
form of the FEBIAD (Forced Electron Beam Induced
Arc-Discharge) ion source [9].
The surface ionization ion source will be used to
ionize elements with low ionization potential elements
such as: the alkalis (Li, Na, K, Rb, Cs and At), alkalineearths (Be, Mg, Sr, Ba and Ra), Group IIIB elements (
Sc, Y, La and Ac) and rare-earths (Ce-Lu). The
FEBIAD ion source is a high efficiency electron
impact ionization source that has demonstrated
efficiencies as high as 50% for Xe and 36 % and ~ 50
% for low melting point metals with high vapor
pressure (Cu, Zn, Ga, Ge, As, Se, Ag, Cd, In, Sn, Sb,
and Te) and efficiencies close to 10% even for high
melting point metals with low vapor pressure (Fe, Co,
Ni, Zr, Nb, Mo, Tc, Ru, Rh, and Pd ).
RIB Production
Radioactive nuclei are produced in proton-induced
nuclear fission, transfer reactions or heavy-ion fusion
reactions by using the 20 UR tandem accelerator.
Proton-induced fission is a useful and powerful
method for producing medium-heavy neutron-rich
nuclei. An estimated distribution of the production
rates for our beam conditions is shown in Fig. 2 [7].
We plan to use many of these fission fragments in our
RIB
research
program.
The ISOL System
The existing ISOL is a Danfysik isotope mass
separator with a 55゜ analyzing magnet and radius of
curvature of 1.5 m. The measured mass resolution of
the system is: M/∆M ≅1250 [10]. Mixing with other
isobaric ions is unavoidable in this ISOL system.
Mixing must be reduced as much as possible by
adjusting ion source parameters to the worst conditions
for efficiently ionizing isobaric contaminants which
have chemical and physical properties different than
those of the specie of interest.
FIGURE 2. Rate distribution of fission products from
proton-induced fission of 238U for 3 µA, 30 MeV protons.
Charge Breeding, Beam Transport And
Stable-Ion Beam Injection
Uranium-carbide targets
The technology of the Electron Cyclotron
Resonance Ion Source (ECRIS) has greatly advanced.
Recently, it has been applied to charge breeding of
heavy-ion beams [11]. The use of an ECR-type charge
breeder is also very beneficial to our ISOL-based RIB
acceleration system. A charge-to-mass ratio of larger
than 1/7 is required to be able to accelerate beams
throughout the linac system without further electron
Uranium-carbide UC2 is a suitable form for fission
fragment production with high-energy proton beams.
Such targets have been shown to quickly and
efficiently release fission products. A target of less
than 2.6 g will be used to produce fission products
with ~ 100 watt proton beams.
231
stripping accompanied by large beam intensity losses,
as is the case for stable beam acceleration with an
ECRIS. Furthermore, electric power consumption is
further reduced by accelerating high charge-to-mass
ratio beams, especially in the SCRFQ linac.
respectively, at Tanashi. On the other hand, the SC
booster at Tokai runs at 129.8 MHz. In order to inject
beams into the booster, all linac frequencies must be
adjusted to multiples of the beam frequency or the
frequency of the SCRFQ. Fortunately, this adjustment
is easily satisfied with only small increases in the RIB
linac frequencies of 1.8 %, corresponding to
frequencies of 25.96 and 51.92 MHz, respectively [14].
Key parameters for the SCRFQ and IH linacs are listed
in Table 1. A buncher is placed between the two linacs.
Charge breeder
An electro-magnetic charge breeder is under
development by S. C. Jeong, et al at KEK [12, 13].
The maximum field of the mirror magnets is 1.5 T. A
mirror correction coil is placed near the ECR plasma
region. A permanent sextupole magnet of 300 mm in
length and 82.5 mm in inner diameter produces the
maximum field of 1.1 T at the wall of the plasma
chamber. Charge breeding experiments began with Ar
and Xe ion beams from which preliminary results have
been obtained. The breeding efficiencies, obtained in
July, 2002,.for Ar and Xe were 14% for 8+ and 6.5%
for 20+, respectively.
Split-coaxial RFQ linac
The SCRFQ linac. built at KEK-Tanashi (INS), is
composed of four cavities, one of which is shown in
Fig. 3 [3]. The split coaxial cavities form a compact
structure designed for very low frequency operation.
The linac can bunch and accelerate more than 90% of
an incident d. c. beam.
TABLE 1. Key parameters of RIB linac.
SCRFQ linac
frequency
25.96 MHz
injection beam energy
2.1 keV/u
output beam energy
178.4 keV/u
tank length
8.6 m
min. q/A
1/29
max. vane voltage
112.5 kV
beam transmission
91 %
duty factor
30 % for q/A=1/29
Low energy beam transport line
Low energy beams of 2 keV/u from the ISOL are
transported to the charge-breeder and from the chargebreeder to the SCRFQ linac. The beam line is rather
long and complicated because of space limitation for
installing the linac systems. The low energy beam line
consists of 3 electro-static deflectors and 3 bending
magnets and 32 electrostatic quadrupole focusing
elements located in straight sections of the beam line
[12]. The magnet, located at the down stream of the
charge breeder, acts as a mass separator with a massresolving power, M/∆M ≅ 50.
IH linac
frequency
number of tanks
focusing
synchronous phase
injection beam energy
output beam energy
total length
min. q/A
acceptance
duty factor
Stable-ion beam injection
The RIB acceleration system will be equipped with
an ECRIS as a stable-ion beam injector. This
capability will be very useful for setting up the linacs
prior to RIB acceleration as well as for setting up RIB
experiments. Another principal purpose of the stable
beam injection system, in the future, is to increase the
beam intensity and beam species by using the linac
system as an injector for the SC booster, instead of the
tandem accelerator. This plan will be realized by
addition of a pre-booster linac described later.
The RIB Linac
The RIB linac consists of a SCRFQ and IH linac,
initially operated at 25.5 MHz and 51 MHz,
232
51.92
4
inter-tank Q-triplet
-25°
0.176 MeV/u
0.176-1.09 MeV/u
5.8 m
1/10
1.7 π mm・mr
100 %
pair of 90 ゜ achromatic bending magnets and two
bunchers will be positioned in the transport line.
The Pre-booster
A pre-booster is needed to further boost 1 MeV/u
beams to 2 MeV/u prior to their injection into the SC
booster. Two options are available for the pre-booster;
a normal-conducting IH-type linac and a SC linac.
Both systems will operate at the same frequency as the
SC booster (129.8 MHz).
M. Tomizawa et al (KEK) have investigated an IH
linac [14]. The IH-2 linac will be composed of 2 tanks
and an inter-tank quadrupole triplet lens, with
respective tanks lengths of 3.1 m. This linac system
will be followed by a quadrupole triplet that will be
used to inject into the SC booster. The minimum
charge-to-mass ration for the linac is set at 1/7.
FIGURE 3. Structure of the split coaxial RFQ linac built by
KEK for RIB acceleration. One part of four is shown.
Inter-digital H type linac
On the other hand, S. Takeuchi, et al (JAERI) have
proposed a SC linac structure with an optimum-β of
about β=0.06. A suitable acceleration structure is a
dual quarter-wave resonator which has two centerconductors terminated with a drift tube in an outer
conductor [15]. An illustration of the structure for the
pre-booster is given in Fig. 5. Approximately twelve
dual-quarter-wave resonators are required in order to
increase the energy of beams with q/A greater than 1/7
up to 2 MeV/u.
The IH linac is a separated function drift tube linac
composed of four inter-digital H-mode type highimpedance cavities and three quadrupole triplets as is
shown in Fig.4 [4]. The output beam energy can be
varied by variation of drift tube voltages and phases.
The duty factor is 100%.
FIGURE 4. Structure of the inter-digital H-type linac built
by KEK for RIB acceleration.
Further Acceleration By The SuperConducting Booster Linac
FIGURE 5. A conceptual drawing of the dual-quarterwave line structure.
RIBs from the IH linac must be boosted in energy
in order to perform nuclear physics research at the
facility. Plans call for extending the beam transport
line from the RIB linac to the SC booster and adding a
pre-booster, after the RIB linac system is completed. A
233
Super-conducting booster
Ein /A (MeV/u)
The SC booster is an independently phased linac
composed of 40 SC quarter wave resonators of
optimum β = 0.1 [16,17]. A cut-away view of the
resonator structure is shown in Fig. 6. Figure 7 shows
the transit time factors (factors for increasing the beam
energy) for a three-gap resonator with an optimum-β
of 0.06 for the pre-booster and a two-gap quarter-wave
resonator with optimum-β of 0.10 used in the SC
booster. As noted, the transit time factor of the
resonators are spread over a wide range of incident
beam velocity, β. The resonators have performed very
well since 1994 without any significant problems or
appreciable performance degradations. The field
gradients have been operated as high as 5 MV/m at an
rf power input of 4 watts [5]. The beam energy
increases at resonator i is given by
1
1
2
10
5
Transit Time Factor
0.8
0.6
0.4
2 gap quarter-wave resonator
β opt (= 0.1)
3 gap dual quarter-wave resonator
β opt =( 0.06)
0.2
0
0
0.05
0.1
0.15
0.2
β
FIGURE 7. Transit time factors for the 2 gap quarter wave
line structure of the booster with the optimum beam velocity
of β = 0.1 and a 3 gap structure with an optimum beam
velocity of β = 0.06 as a function of β =beam velocity/c.
∆Ei = q Eacc,i L TTF(βi) cos(φi)
The output beam energy from the booster is shown in
Fig. 8 as a function of charge-to-mass ratio q/A, in
which the acceleration field gradient and the
synchronous phase are assumed to be 5 MV/m and
−20 degree for every resonator, respectively. Since the
resonator number will be reduced to 36 when the SC
accelerating structure is employed for the pre-booster,
two curves for 40 and 36 resonators are presented in
Fig. 8. The reduction in number of resonators will
permit operation of all of the resonators, including the
low-β resonators, with the existing cryogenic system.
In either case, one can expect an output energy of
about 5.5 MeV/u to 8 MeV/u for beams with a chargeto-mass ratio of 1/7 to 1/4.
where q is the charge-state of the beam; Eacc is the
acceleration field gradient averaged over the
acceleration length L; TTF is the transit time factor at
beam velocity β, normalized to the optimum β; and φ
is the synchronous phase. The synchronous phase can
be freely set for different incident particles as an
advantage of the independently phased linac.
10
9
E out/A (MeV/u)
8
7
6
5
40 resonators
36 resonators
4
3
2
0.05
0.1
0.15
0.2
0.25
0.3
q/A
FIGURE 6. Cut-away view of the quarter wave
resonators used in the 129.8 MHz SC booster with optimum
β =0.1.
FIGURE 8. Output beam energy per nucleon from the
booster as a function of charge-to-mass ratio, calculated for
the 40 and 36 resonators.
234
Strasser, P, Kubono, S. and Nomura, T., Nucl. Phys.
A701, 62c (2002).
PRESENT STATUS AND REMARKS
Construction of the room for the RIB accelerator
and experimental equipment began in FY 2002. The
room is equipped with a powerful ventilation system
and a closed drain system for safety reasons. A utility
building was built in 2001 next to the RIB accelerator
room for housing place rf power supplies, the cooling
system, transformers, etc. The work related to the
buildings has been shared by operating group members
of the tandem accelerator, S. Kanda et al. The RIB
linacs will be brought on-line in FY 2003, after
frequency adjustments. A charge breeder has been
built and experiments are carried on at KEK-Tsukuba.
We are expecting the first RIB acceleration in 2004,
although we have to solve many problems, especially
those related to RIB production. The IH-2 structures
and the low-β resonators for the pre-booster need
further development, as well as more funds for
completion.
3. Arai, S., Imanishi, A., Niki, K., Okada., M., Takeda, Y.,
Tojo, E. and Tokuda, N., Nucl. Instrum. and Meth.
A390, 9 (1997).
4. Tomizawa, M., Arai, S., Arakaki, Y., Imanishi, A.,
Okada, M., Niki, K., Takeda, Y. and Tojyo, E., “Exotic
Ion Beam” in Heavy Ion Accelerator TechnologyArgonne 1998 edited by K. Shepard, AIP conference
proceedings 473, New York: American Institute of
Physics, 1998, pp. 451-465
5. Takeuchi, S., Abe, S., Hanashima, S., Horie, K., Ishizaki,
N., Kanda, S., Matsuda, M., Ohuchi, I, Tayama, H.,
Tsukihashi, Y. and Yoshida, T, “Electrostatic
Accelerator” in Heavy Ion Accelerator TechnologyArgonne 1998 edited by K. Shepard, AIP conference
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Physics, 1998, pp. 152-167.
6. Matsuda, M., Kobayashi, C. and Takeuchi, S.,
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ACKNOWLEDGMENTS
We would like to sincerely thank Drs. S. Tanaka, A.
Iwamoto and T. Nomura for their efforts to promote
the RIB collaboration project between JAERI and
KEK. The dedicated contributions of the following
members to this RIB project are fully appreciated by
the author:
7. Tsukada, K, private communication.
8. Ichikawa, S., Osa, A., Matsuda, M., Tsujkada, K., Asai,
M., Nagame, Y., Jeong, S.C. and Katayama, I, to be
published in Proceedings of the EMIS14 Conference2002.
9. Kirchner, R., Nucl. Instrum. and Meth., 133, 187 (1976).
(JAERI) S.Abe, N. Ishizaki, S. Kanda, I. Ohuchi, H.
Tayama, Y. Tsukihashi, S. Hanashima, M. Matsuda, T.
Nakanoya, T. Yoshida, A. Iwase, H. Iimura, A. Osa, M.
Oshima, M. Sataka, H. Ikezoe, K. Nishio, S. Ichikawa,
K. Tsukada, Y. Nagame, S. Mitsuoka,
10. Ichikawa, S., Sekine, T., Iimura, H., Oshima, M. and
Takahashi, N., Nucl. Instrum. and Meth. A274, 259
(1989).
11. Geller, R., Bouly, J. L., Bruandet., J.F., Chauvin, N.,
Curdy, J.C., Lamy, T., Nifenecker, H., Sole, P., Sortais,
P. and Vieux-Rochaz, J.L., “ION SOURCES” in Heavy
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(KEK) I. Katayama, H. Miyatake, H. Kawakami, M,
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Niki, M. Tomizawa.
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