Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 52 (2019)

Superconducting RILAC booster†N. Sakamoto,∗1 M. Dantsuka,∗1 H. Hara,∗3 H. Imao,∗1 E. Kako,∗2 O. Kamigaito,∗1 K. Kusaka,∗1 K. Miyamoto,∗3H. Nakai,∗2 H. Okuno,∗1 K. Ozeki,∗1 H. Sakai,∗2 K. Sennyu,∗3 K. Suda,∗1 K. Umemori,∗2 T. Watanabe,∗1Y. Watanabe,∗1 K. Yamada,∗1 and T. Yanagisawa∗3The RIKEN Heavy-Ion Linac (RILAC) is undergoing an upgrade to enable it to further investigate superheavy elements and produce of radioactive isotopes for
medical applications. In this project, a new superconducting (SC) electron cyclotron resonance ion source andSC booster linac (SRILAC) are being developed andconstructed. The SRILAC consists of 10 TEM quarterwavelength resonators that are operated at 73 MHz andcontained in three cryomodules (CMs). The goals of
the upgrade are listed in Table 1. It should be notedthat the fundamental frequency of the reference radio
frequency (RF) signal has been chosen as 36.5 MHz because it is the frequency for the RF system of the RIBF
accelerators.
As shown in Fig. 1, the SRILAC consists of three
CMs–CM1, CM2, and CM3–with a room-temperature
medium-energy beam transport (MEBT) between them.
The CMs do not contain superconducting magnets. The
design of the CMs is a modiﬁcation of a prototype CM
developed at RIKEN.1–3)
The operational parameters of the CMs are listed inTable 2. The gap length of the cavity is optimized for
β = 0.08 particles with a transit time factor (TTF) of0.9. The gap voltage is 1.2 MV, which corresponds toan acceleration gradient Eacc of 6.8 MV/m with a synchronous phase of −25◦ . After the fabrication of theten SC-cavities, all cavities were tested and passed theacceptance test.5)
The SC-cavities are cooled by 4-K liquid helium provided by a liquid helium cryogenic system using a HELIAL MF refrigerator (Air Liquide).
RILAC

SRILACMEBT Top View

Liquid Helium Transfer Line

A1

CM1

A2

CM2

CM3

Beam
Differential Pumping System

BeamFloor

CM1

A2

CM2

∗1
∗2
∗3Before
12 DTLs
37.75/75.5
25 (A/q = 5)After
8 DTLs, 3 CMs
36.5/73.0
39 (A/q = 6)

Table 2. Operational parameters of the SRILAC.
Frequency (MHz)Einj (MeV/nucleon)
Eext (MeV/nucleon)
Number of cavities
Cavity typeMax. gap voltage (MV)
Synchronous phase (◦ )Max. acc. gradient (MV/m)
Target Q0 (at Eacc = 6.8 MV/m)
Beam current (µA)
Qext
Amplifier output (kW)73.0 (c. w.)
3.6
6.5 for A/q = 610TEM, λ/4
1.2
−25
6.8
1 ×109≤100
1–4.5 ×106
7.5

For the MEBT, a newly designed beam energy position monitor will be employed instead of the traditional wire scanners. Because beam measurement is
non-destructive, ideally there is neither outgassing nor
spattering to produce particulates in the high-vacuum
sections.
Because the SRILAC will be installed in the existing
facility, it is important to have an isolation system indicated as a diﬀerential pumping system in Fig. 1 toprevent contamination of the SC-cavities, which deteriorates the performance of the SC-cavities.
Full assembly of the CM will be ﬁnished in the ﬁrst
quarter of 2019 and its installation in the accelerator
building is scheduled for March 2019. After installing
the MEBT, including the diﬀerential pumping systems,
cooling and RF testing will be performed during thesecond quarter of 2019 with the aim of full beam commissioning in the third quarter of 2019.
References

CM3Fig. 1. Layout of the Superconducting RILAC (SRILAC).
†Upgrade
Number of tanks
Frequency (MHz)Total Vacc (MV)Side View

1300 mm

A17540 mm

Table 1. Specifications of RILAC before and after upgrade.

Condensed from the proceedings of LINAC2018, Beijing,
September 2018, WE2A03, p. 620.
RIKEN Nishina Center
KEK, Tsukuba
MHI-MS, Kobe- 12 -1) K. Ozeki et al., Cryomodule and power coupler for
RIKEN Superconducting QWR, LINAC2016, East Lansing, September 2016, TUPLR061, p. 598.
2) K. Yamada et al., First Vertical Test of Superconducting
QWR Prototype at RIKEN, LINAC2016, East Lansing,September 2016, THPLR040, p. 939.
3) N. Sakamoto et al., SRF2017, WEYA01; K. Yamada etal., PASJ 14th Annual Meeting, TUOL02.
4) http://www.jst.go.jp/impact/en/program/08.html
5) K. Yamada et al., Performance test of bulk-niobium cavities for new superconducting linear accelerator, in thesereports.