The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

PRESENT STATUS OF THE RIKEN HEAVY-ION LINAC
O. Kamigaito1, M. Kase, N. Sakamoto, E. Ikezawa, S. Kohara, M. Fujimaki, T. Nakagawa,
M. Kidera, Y. Higurashi, H. Ryuto, Y. Chiba, M. Hemmi, Y. Miyazawa, T. Chiba,T. Aihara2, T. Ohki2, H. Hasebe2, H. Yamauchi2, A. Uchiyama2, K. Oyamada2,
A. Goto, and Y. Yano,
RIKEN, Wako-shi, Saitama, 351-0198, JapanAbstract
The RIKEN heavy-ion linac (RILAC) was successfully
upgraded, by adding a booster consisting of six
resonators. Various heavy ion beams have been
accelerated to the energies around 5 MeV/u with very
high intensities. For example, 64Ni beam of more than
one particle-micro-ampere is available in the cw mode.
The stability of the rf-system, as well as the transmission
efficiency, have been improved. On the other hand, weexperienced serious problems mainly due to the high rfpower required for the acceleration. Using the upgradedbeams, systematic study on search for super-heavy
elements is under way; elements 110 and 111 have been
produced so far.

1 OVERVIEW
The layout of the RILAC facility is illustrated in Fig. 1.
The main linac[1], which has been operated since 1981,
consists of six variable-frequency resonators (RILAC 1 6). The voltage gain of the main linac was designed to be
16 MV in the frequency range from 17 to 45 MHz. The
rf-amplifiers for the last two resonators (RILAC 5, 6)
were replaced in 1999.
There are two injectors for the main linac. One is theCockcroft-Walton injector of 450 kV, which wasinstalled in 1980. On the high voltage terminal, an ECR
ion source (ECRIS) of 8 GHz (NEOMAFIOS) is placed.
The other is a variable-frequency RFQ (FC-RFQ)[2] withan 18-GHz ECRIS[3], installed in 1996. The output
voltage of the RFQ is the same to that of the CockcroftWalton injector. Owing to the high performance of the18-GHz ECRIS, the beam intensity has increased
remarkably.
The booster, consisting of six resonators, wasconstructed in 2000 in order to increase the beamenergy[4]. The first two resonators are frequencyvariable, whereas the other four are fixed-frequency type.
The resonant frequency is set twice as that of the mainlinac. The designed value of the voltage gain is 16 MV.
The commissioning of the booster started in 2001, andwe got the license for the upgraded operation in March
2002.
Figure 1 also shows the beam transport line and theexperimental apparatus. The transport system has one
main line, transferring the beam from the RILAC to thering cyclotron (RRC), and six branches (e1 - e6 in Fig. 1)
for various experiments. Among the six beam lines, thee3 beam line is dedicated for the gas-filled recoil isotope
separator (GARIS), where the experiments of search forsuper-heavy elements are carried out.
The most important feature of the RILAC is that theacceleration is performed in the continuous wave (cw)
Magnetic Rigidity

Prebuncher
4 - 38.2 MHz

5.8 MeV/u
M/q < 5.6e1
4.0 Tme2 e3
2.1 Tme4 e5 e6 1.2 Tm

Re-buncher
18 - 38.2 MHz
RCA4648
110 kW
17 - 45 MHz

RCA4648
150 kW
17 - 45 MHz

RCA4648
180 kW
17 - 45 MHz

RCA4648
220 kW
17 - 45 MHz

RS2058CJ
100 kW
36 - 76.4 MHz

RS2042SK250 kW
18 - 42 MHz

GARIS

e3e2

e4

18GHz ECRIS

e5
Solenoid
Booster-A5, 675.5 MHz

FC-RFQ18 - 38.2 MHz

Stripper123456RILAC-1
17 - 45 MHz

RILAC-2
17 - 45 MHz

RILAC-3
17 - 45 MHz

RILAC-4
17 - 45 MHz

RILAC-5
17 - 45 MHz

RILAC-6
17 - 45 MHz

e1

4CW50000E
40 kW
From Cockcroft-Walton

Booster-A1, 2
36 - 76.4 MHz

Booster-A3, 475.5 MHze6Buncher
17 - 45 MHz

Buncher
34 - 90 MHz

0510 mFig. 1: Schematic drawing of the RILAC facility.
12kamigait@postman.riken.go.jp
SHI Accelerator Service, Ltd.

RS2058CJ
100 kW
36 - 76.4 MHzto RRC
Decelerator-D1
36 - 76.4 MHz

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

mode. Another important property is the variability of
the frequency, which makes it possible to acceleratevarious kinds of ions. Available beam energies aresummarized in Table 1, along with the maximum massto-charge ratio acceptable by the RILAC.
Table 1: Beam energy in the RILAC facility
Eout
ResonatorsfM/q**(MeV/u)(MHz)*2RILAC
18 - 420.00202×f 2 8000 / f(Main linac)
RFQ+RILAC
18 - 38.2 0.00271×f 2+A1+A2
RFQ+RILAC
37.75
5.8
5.6
+A1~A6*Resonant frequency of the main linac (RILAC 1 - 6).
**Designed value of the acceptable mass-to-charge ratio.

2 OPERATION STATUS
Table 2 shows the statistics of the RILAC operationfrom January 1 through December 31, 2002[5]. Although
we met a lot of problems, the beam time amounts to4,500 hours.
Table 3 summarizes the number of days allocated todifferent research groups[5]. Since we got the upgradedlicense, nuclear physics experiments have become majorpart of the beam time. The percentage of the beam timeused by the RRC was 32 % of the total.
The accelerated ions in the last year are the followings:
4He2+, 40Ar8+, 11+, 48Ca11+, 58Fe13+, 58Ni9+, 64Ni13+, 14+,84
Kr8+, 17+, 19+, 20+, 86Kr20+, 136Xe18+, 20+, 27+, 181Ta20+, and209 20+
Bi . For more than 95 % of the beam time, the ionswere fed by the 18-GHz ECRIS. The beam time of 64Ni
amounts to 52 days, which is about 30 % of the total. The86
Kr and 48Ca ions were accelerated by the RILAC
together with the booster (A1 and A2) and injected into
the RRC with a harmonic number of 8.
Table 2: RILAC operations from January 1 throughDecember 31, 2002.
%
No. of Days
Beam time187
51.2
Overhaul and improvement77
21.1
Scheduled shutdown
68
18.6
Periodic inspection & repair
33
9.0
Total
365
100

Table 3: Beam time allocation.
No. of Days
Nuclear physics
83
Beam transport to RRC
60
Radiation chemistry
13
Material analysis
12
Atomic physics
11
Accelerator research
8Total
187%
44.4
32.1
7.0
6.4
5.9
4.3
1003 IMPROVEMENTS AND TROUBLES
The transmission efficiency of the beam through thelinac, from the 18-GHz ECRIS down to the exit of thebooster, was not so good. The typical value stayed around30 - 40 %. The beam loss mainly takes place in theinjector section, from the ion source to the entrance ofthe main linac.
One of the reasons for the beam loss is considered tobe a mismatch of the transverse emittance to theacceptance of the beam line in the injector section.
However, the only device with which we could control
the beam profile had been the solenoid magnet between
the analyzing magnet and the RFQ.
To improve the transmission efficiency, a newsolenoid magnet was installed between the 18-GHzECRIS and the analyzing magnets[6]. The maximum
magnetic field on the axis is 0.65 T. As a result, thebeam intensity increased by about 50 % at the exit of theanalyzing magnet. The transmission efficiency throughthe linac has also increased; typical value is 50 % now.
We had another problem on the output beam from theRILAC; the longitudinal phase of the beam center was
sometimes quite unstable and the injection of the beam
into the RRC was difficult. From the measurement for
the rf-system of the main linac, it was found that thephase oscillation was large in the region close to thecarrier frequency (∆f < 100 Hz). Therefore, all the phase
control units for the main linac were replaced into newly
designed ones[7]. After this replacement, the phaseoscillation has improved to be less than ± 0.1° in thewhole frequency range. The longitudinal excursion of thebeam has become negligibly small.
On the other hand, new problems appeared as the rfpower increased. One of them is that the thin copper
sheets (10 cm wide, 7 cm long, 0.3 mm thick), used forthe electric contact in the resonators of the main linac,
sometimes melted due to the large rf-current. They were
replaced with thicker ones in this summer.
Another problem is a self-oscillation of the rfamplifier of the last resonator of the main linac (RILAC6); it oscillates at 105 MHz with very high power when
the plate stub is set in a certain position-range. A
measurement has shown that there is a coupled resonantmode between the grid circuit and the plate circuit, bywhich the output power is fed back to the input circuit in
the positive phase. Although this oscillation is temporary
suppressed by mounting dumping resistors in the platecircuit, the problem is not fully solved yet.

4 EXPERIMENTS WITH RILAC
In this section, two topics are briefly represented
among the experiments performed with the RILAC.

The 14th Symposium on Accelerator Science and Technology, Tsukuba, Japan, November 2003

4.1 Super-heavy element search
Research experiments on super-heavy elements began
in March 2002 with GARIS at the e3 beam line. First,the beams of 40Ar, 48Ca, and 58Fe with energies of 4.6 –4.9 MeV/u were used in order to study the characteristicsof the GARIS.
In July 2002, a confirmation experiment on thesynthesis of element 110 started using a 64Ni beam withan energy of 5.0 MeV/u, through the fusion reaction
208
Pb + 64Ni → 271110 + n. The total service time for theexperiments was 1486.5 hours. The 18-GHz ECRIS with
the MIVOC (Metal Ions from Volatile Compounds)
method[8] and the booster resonators worked actively toprovide these beams with high intensity for a very longtime. Finally, 14 candidates of decay chains originatingfrom 271110 were observed, and the excitation function ofthe reaction was measured successfully[9].
The typical beam intensity had exceeded one particlemicro-ampere on the target throughout this experiment.
The voltage gain of the booster was 10.6 MV, which was
65 % of the designed value.
From February to May 2003, a confirmation
experiment on the element 111 was performed using a64
Ni beam on 209Bi targets. The total service time was930.5 hours. The excitation function of the reaction wasalso measured successfully, where 14 candidates of decay
chains were observed[10].

4.2 H=8 mode acceleration of the RRC
The harmonics of the rf-system of the RRC is designed
to be 9 when the RILAC is used as an injector. The
additional velocity gain through the booster makes it
possible to operate the RRC in the harmonics of 8, whichindicates that the extraction velocity can be boosted by afactor of 9/8 at the same rf-frequency[11]. This energy
gain is very useful to produce more intense radioactive
beams far from stability. Based on this acceleration
scheme, more than 100 particle-nano-ampere of 48Ca
beam was accelerated up to 63MeV/u in order to apply to
new isotope search, resulting in discovery of the newisotopes 34Ne, 37Na, and 34Si[12]. Recently, 86Kr beam of
63 MeV/u was extracted from the RRC with the beam
intensity of 100 particle-nano-ampere.

5 FUTURE PLAN
As mentioned above, most of the beams are provided
with the 18-GHz ECRIS. The ion source, however,requires periodic cleaning especially in the MIVOC
method, which means that the beam time is stopped
during the maintenance.
To make this intercept as small as possible, we areplanning to construct another ECRIS and install it inparallel with the present one. The beam line from theCockcroft-Walton injector will be removed at the sametime. A planned layout is shown in Fig. 2. Two

Solenoid

PresentECRIS

Solenoid
RILAC-1

New ECRIS

FC-RFQ
01

23m

Fig. 2: Planned layout of the new injector with two ion
sources.
analyzing magnets are connected back to back and they
are rotated by 90 degree without opening the vacuumchamber. This configuration will allow us to test one ofthe ion sources while the other is in use for the beamtime. The magnets have been already fabricated. The
installation will be carried out in the next year.

6 ACKNOWLEDGMENT
We are grateful to the Safety Center, RIKEN for thecooperation in monitoring the radiation in theexperimental room. The construction of the fixedfrequency resonators (A3 ~ A6) of the booster wasfunded by Center for Nuclear Study, University of Tokyo.

REFERENCES[1] M. Odera et al., Nucl. Instrum. Methods 227, 187(1984).
[2] O. Kamigaito et al., Rev. Sci. Instrum. 70, 4523
(1999).
[3] T. Nakagawa and Y. Yano, Rev. Sci. Instrum. 71,637 (2000).
[4] O. Kamigaito et al., Proc. 26th Linear Accelerator
Meeting in Japan, Tsukuba, p. 43 (2001).
http://conference.kek.jp/LAM26/LAM26PDF/1C5web.PDF[5] E. Ikezawa et al., RIKEN Accelerator Progress
Report 36, 3 (2003).
[6] Y. Higurashi et al., RIKEN Accelerator Progress
Report 36, 277 (2003).
[7] N. Sakamoto et al., RIKEN Accelerator Progress
Report 36, 283 (2003).
[8] H. Kovisto et al., Nucl. Instrum. Methods Phys. Res.
B 94, 291 (1994).
[9] K. Morita et al., to be submitted to European
Physical Journal A.
[10] K. Morita, Proc. VIII International Conference on
Nucleus-Nucleus Collisions, Moscow, Russia, 2003,
to be published.
[11] M. Kase et al., RIKEN Accelerator Progress Report36, 5 (2003).
[12] M. Notani et al., Phys. Lett. B 542, 49 (2002)