RIKEN Accel. Prog. Rep. 50 (2017)

Research Activities 1991–2016

Development of ECR ion sources at RIKEN
T. Nakagawa ∗1
The electron cyclotron resonance ion source(ECRIS) is one of the best choices for the RI Beam
Factory (RIBF) project 1) for the production of radioisotope beams using projectile-like fragmentationand for super-heavy element search experiments.2)
Since the ﬁrst beam was produced with the RIKEN
10 GHz ECRIS,3) we have continuously improved
the performance of the existing ECRIS and constructed new ECRISs to produce intense beams ofhighly charged heavy ions to meet the requirementsof the RIKEN accelerator facility. For these purposes,
we have constructed three types of high-performance
ECRISs (18 GHz ECRIS, Liquid-He-free SC-ECRIS,
and 28 GHz SC-ECRIS) in the last three decades.
In particular, we have attempted to produce intense
beams of heavy ions, such as uranium (U) ions for
the RIKEN RIBF project 1) and super-heavy element
search experiment 2) since the early 2000s. Figure 1
shows the time evolution of the beam intensity ofhighly charged heavy ions produced at RIKEN. In thelast three decades, the beam intensity has been dramatically increased, as shown in the ﬁgure. For example, the beam intensity of Ar8+ has been increased
from ∼100 μA to 2 mA. For heavier ions, the intensity of the U35+ ion beam increased from a few μA to∼180 μA in the last 10 years.
The 18 GHz ECRIS,4) which consists of two roomtemperature solenoid coils and a hexapole permanent
magnet to conﬁne the plasma for producing mainly
medium-charge-state heavy ions such as Ar8+ andXe20+ and works as an external ion source of theRIKEN linear accelerator (RILAC), was constructed
in 1995 and produces intense beams of various heavy
ions (∼2 mA of Ar8+ , ∼200 μA of Xe20+ ). To increase the variety of ion species, we adopted the various
methods 5,6) to produce intense beams of metallic ions.
In the early 2000s, intense beams of highly charged
Zn ions were required to perform a new super-heavy
element (Z = 113) search experiment. To meet the requirement, we adopted the insertion method and successfully produced an intense beam of highly charged
Zn ions (∼2 pμA) for a long term (longer than onemonth) without a break.
Liquid-He-free SC-ECRIS 7) has a unique feature inthat it uses a small refrigerator to achieve the superconductivity of the magnet without using liquid He.
It produces a high mirror magnetic ﬁeld (maximum
magnetic ﬁeld of ∼3 T) with low electric power consumption. It is suitable for producing higher charge
states of heavy ions. For this reason, it is used as anexternal ion source of the AVF cyclotron, which only
accepts higher-charge-state heavy ions (A/q < 4) foracceleration.
A fully superconducting ECRIS with 28 GHzmicrowaves 8) was constructed in 2007. The RIKEN
SC-ECRIS can be operated at ﬂexible axial ﬁeld distributions from the so-called classical Bmin to ﬂat Bmin .9)
In 2013, U35+ ion beams of ∼180 μA were produced at
an injected RF power of several kW for a short-term
test experiment using the sputtering method.10) It produced a U35+ beam of ∼120 μA for the RIKEN RIBF
experiment with a high-temperature oven.11) Figure 2shows a schematic of the ion source. Figure 3 shows thecharge-state distribution of the highly charged U ion
beam when tuning the ion source to produce U35+ ions.

RIKEN 28GHz SC-ECRISRIKEN 10GHz ECRISRIKEN 18GHz ECRIS

Beam inetnsity (PA)Gyrotron (28GHz)(10kW max)
SC-ECRIS

103

Ar8+
Kr13+

102

Solenoid coil

U35+

Xe20+

Vacuum window

Analyzing magnet

101
100

1990

2000
Year

2010

2020

Fig. 1. Time evolution of the beam intensity of highly
charged heavy ions produced at RIKEN ECRISs.
∗1DC cutFig. 2. Schematic drawing of the RIKEN 28 GHz SCECRIS.

RIKEN Nishina CenterS-56

Research Activities 1991–2016

RIKEN Accel. Prog. Rep. 50 (2017)

Beam intensity(ePA)600
16O2+16O4+

400
16O6+U ion

2000

Beam intensity(ePA)050
100
Analyzing magnet current(A)
300

U35+
200

150

U33+
U31+

U37+

16O2+100

080

90

100

Analyzing magnet current(A)Fig. 3. Charge-state distribution of the U ion beam. Theion source was tuned to produce the U35+ ion beam.

For the new super-heavy element (Z = 119) search experiment, an intense beam of highly charged V ionbeams was required. We therefore attempted to produce a highly charged V ion beam using the RIKEN
28 GHz SC-ECRIS and produced a V12+, 13+ ion beamof a few hundred μA for a short-term test experiment;
its intensity is almost ten times higher than that of theZn ion beam.
References
1) Y. Yano, Nucl. Instrum. Methods Phys. Res. B 261,1009 (2007).
2) K. Morita et al., Nucl. Phys. A 944, 30 (2015).
3) K. Hatanaka et al., RIKEN Accel. Prog. Rep. 22, 219(1988).
4) T. Nakagawa et al., Nucl. Instrum. Methods Phys. Res.
B 226, 392 (2004).
5) T. Nakagawa et al., Nucl. Instrum. Methods Phys. Res.
A 396, 9 (1997).
6) K. Ozeki et al., Rev. Sci. Instrum. 86, 016114 (2015).
7) T. Kurita et al., Nucl. Instrum. Methods Phys. Res. B
192, 429 (2002).
8) T. Nakagawa et al., Rev. Sci. Instrum. 81, 02A320(2010).
9) G. Alton, D. N. Smithe, Rev. Sci. Instrum. 65, 775(1994).
10) Y. Higurashi et al., Rev. Sci. Instrum. 85, 02A953(2014).
11) J. Ohnishi et al., Rev. Sci. Instrum. 87, 02A709(2016).

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