Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 52 (2019)

Construction of New 28-GHz ECR ion source for RILAC
T. Nagatomo,∗1 Y. Higurashi,∗1 J. Ohnishi,∗1 A. Uchiyama,∗1 K. Kumagai,∗1 M. Fujimaki,∗1 T. Nakagawa,∗1T. Ohki,∗2 M. Tamura,∗2 K. Kaneko,∗2 K. Oyamada,∗2 A. Yusa,∗2 H. Yamauchi,∗2 and O. Kamigaito∗1Since 2017, we have been upgrading the RIKEN
linear accelerator RILAC for the RIBF project1) andto synthesize new super-heavy elements (SHEs) withatomic number Z ≥ 119. In the upgrade,2) some of thelatter acceleration cavities of RILAC were planned to bereplaced with superconducting quarter-wavelength resonators (SC-QWRs) to increase the energy of the beamwith M/Q = 6 from 5 MeV/nucleon to 6 MeV/nucleon
for the synthesis of SHEs. In the SHE project, thehigh intense metallic ion beams, such as Va and Cr(> 10 particle µA), are required from the ion source.
In addition, because the SC-QWRs are driven by theﬁxed frequency, these SC-QWRs are skipped in thevariable frequency operation especially for the RIBF
project. Thus, high-intensity ion beams with a higher
charge than before. For example, Ca16+ beam of∼ 100 electric µA is required to achieve enough energy
without the SC-QWRs to meet the variable frequency
acceleration scheme of RIBF. To meet these requirements, we decided to construct a new electron cyclotron
resonance ion source that consists of fully superconducting mirror magnets (SC-ECRIS) with a high-power
28 GHz gyrotron microwave generator.
Figure 1 shows the current status of the new 28 GHz
SC-ECRIS and gyrotron microwave generator with low
energy beam transport (LEBT) constructed in the injection room of the RILAC accelerator building. TheSC-ECRIS and microwave generator are the same models as the uranium ion source of RILAC II, which is predominantly used for RIBF project (for details, please
see the references).3–5) The new SC-ECRIS is designed
to be operated with 18 and 28 GHz microwaves. InFig. 1, the LEBT following the ECRIS consists of asolenoidal lens, an analyzing magnet sandwiched by twosteering magnets, a diagnostics chamber, and anothersolenoidal lens. In the diagnostics chamber, a Faradaycup and a pepper-pot type emittance meter (PPEM)
were installed. The 40 Ar11+ beam of ∼ 90 electric µA
was successfully extracted from the new SC-ECRIS as
the ﬁrst beam with the 18 GHz microwave because the28 GHz microwave generator was not ready at thattime. Figure 2 shows the beam proﬁle (x-y plot) andhorizontal emittance (x-x′ plot) of 40 Ar11+ beam withthe 18 GHz microwave of 700 W using the PPEM. In
Fig. 2, the beam has a characteristic triangular hollow
shape with widely spread emittance along the horizontal. The triangular shape is formed by the hexapolar
magnetic ﬁeld of the mirror ﬁeld of ECRIS and the ionsare localized into three peripheral regions in the beam.
By selecting one of the three intense regions in the x∗1∗2

RIKEN Nishina Center
SHI Accelerator Service Ltd.

Fig. 1. New 28 GHz SC-ECRIS and LEBT.

Fig. 2. Obtained beam profile (upper) and horizontal emittance (lower) of 40 Ar11+ beam using PPEM. Color indicates the beam intensity in the arbitrary unit.

y space as a red rectangle in the left of Fig. 2, it isfound that the localization in the emittance space also
appears as shown in the right of Fig. 2. From the result,
we can eﬀectively increase the beam brightness, which
is deﬁned as the beam intensity per unit emittance, bysuitable spatial selection of the localized beam using a
combination of slits and steering magnets.
We plan to ﬁnish the preparations for the 28 GHz microwave generator and high temperature oven to generate metallic vapor in the ﬁrst half of 2019.
References
1) Y. Yano, Nucl. Instrum. Methods Phys. Res. B 261, 1009
(2007).
2) O. Kamigaito et al., Proceedings of IPAC2016, Busan,Korea, 1281 (2016).
3) T. Nakagawa et al., Rev. Sci. Instrum. 81, 02A320(2010).
4) Y. Higurashi et al., Rev. Sci. Instrum. 85, 02A953(2014).
5) G. D. Alton et al., Rev. Sci. Instrum. 65, 775 (1994).

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