VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 55 (2022)

Research Facility Development Division
Accelerator Group
1. Abstract
The Accelerator Group, consisting of seven teams, pursues various upgrade programs on the world-leading heavy-ion accelerator
facility, RI Beam Factory (RIBF), to enhance the accelerator performance and operation eﬃciency. The programs include the R&D ofsuperconducting ECR ion source, charge stripping systems, beam diagnostic devices, radio-frequency systems, control systems, andbeam simulation studies. We are also maintaining the large infrastructure to realize eﬀective operation of the RIBF. Moreover, we areactively promoting the applications of the facility to various research ﬁelds.
Our primary mission is to supply intense, stable heavy-ion beams for the users through eﬀective operation, maintenance, andupgrade of the RIBF accelerators and related infrastructure. The director members govern the development programs that are not dealt
with by a single team, such as intensity upgrade and eﬀective operation. We also discuss the future plans of RIBF along with otherlaboratories belonging to the RIBF research division.
Various improvements and developments have been carried out for the RIBF accelerators in order to upgrade the beam intensities
and stability. Owing to the eﬀorts, for example, we succeeded in accelerating the uranium beam of 117 particle nA through SRC in
October 2020. This surpassed the long-standing target of 100 particle nA, and also means that one of goals of the current mid-termplan of RNC has been achieved. Moreover, the beam availability for the RIBF experiments has increased to 98.3% in 2021, which is
the highest value since RIBF started operation.
At the RILAC facility, upgraded with a superconducting ECR ion source and superconducting booster linac, synthesis experimentsof new elements has been conducted since 2020. In the ﬁrst half of 2021, major repairs were made to the normal-conducting cavities.
The coupler part of the superconducting cavities, which had a vacuum leak problem, were modiﬁed during the summer shutdown. As
a result, a high intensity beam of 51 V is now being supplied stably. Moreover, construction of a new beam line for the R&D of mass
production method of 211 At has been almost completed, in cooperation with the Safety Management Group under the leadership of
the RI Application Research Group.
An upgrade plan of RIBF for further increasing uranium beam has been continuously discussed. Based on the basic design of the“charge-stripper ring (CSR),” which will be used to increase the overall stripping eﬃciency of the uranium beam, a pair of quadrupole
magnets was fabricated as a prototype. The measured magnetic ﬁeld was in good agreement with the simulations, including themagnetic ﬁeld leaking around the magnets. Design study of the extraction bending magnet was also performed.

2. Major Research Subjects
(1)
(2)
(3)
(4)

Intensity upgrade of RIBF accelerators (Okuno)
Eﬀective and stable operation of RIBF accelerators (Fukunishi)
Stable operation of the upgraded RILAC facility
Promotion of the upgrade plan of RIBF

3. Summary of Research Activity(1) The beams were provided for the RIBF experiments at the intensities requested by the users.
(2) The beam availability for the RIBF experiments was 98.3% in 2021. This is the highest value since RIBF started operation.
(3) A high intensity beam of 51 V was supplied stably to the synthesis experiments of new elements at the upgraded RILACfacility.
(4) An intensity-upgrade plan of the RIBF has been further investigated. Elemental R&D of the ﬁrst charge-stripper ring (CSR1)
is under progress.

Members
Director
Osamu KAMIGAITO
Deputy Directors
Hiroki OKUNO (for intensity upgrade)

Nobuhisa FUKUNISHI (for stable and eﬃcient operation)

Junior Research Associate
Kaori NAKAMURA
Research Consultants
Tadashi FUJINAWA

Masayuki KASE

Visiting Scientists
Eiji KAKO (KEK)
Hirotaka NAKAI (KEK)
Kensei UMEMORI (KEK)
Hiroshi SAKAI (KEK)Taro KONOMI (KEK)
Masahiro OKAMURA (BNL)
Noboru SASAO (Okayama Univ.)
Yasutaka IMAI (Okayama Univ.)- 251 -VI. RNC ACTIVITIESRIKEN Accel. Prog. Rep. 55 (2022)

Assistant
Karen SAKUMA
Administrative Part-time Worker II
Ryoko UMEZAKI

List of Publications & Presentations
Publication[Original Paper]
O. Kamigaito, “Scale invariance of electrodynamics in radio-frequency linear accelerators,” arXiv:2109.14273.

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