Ⅰ. HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 53

Non-evaporable getter-based diﬀerential pumping system for SRILAC
H. Imao,∗1 K. Yamada,∗1 N. Sakamoto,∗1 T. Watanabe,∗1 Y. Watanabe,∗1 K. Oyamada,∗2 A. Yusa,∗2and O. Kamigaito∗1
Upgrades of the RIKEN heavy-ion linac (RILAC) involving a new superconducting linac (SRILAC1) ) are in
progress. High-vacuum (<10−8 Pa) and particulate-free
conditions are strictly necessary for keeping the performance of the superconductive radio frequency (SRF)
cavities of SRILAC. It is crucially important to develop
neighboring warm sections to mitigate the large diﬀerence in the vacuum and clean conditions with respect tothe existing old RILAC and beamlines built almost fourdecades ago. In the present study, a non-evaporable getter (NEG)-based diﬀerential pumping system (DPS) has
been developed.
The three-stage DPS (Fig. 1) was designed to achievea pressure reduction from the existing beamline vacuum(10−5 –10−6 Pa) to an ultra-high vacuum of less than
10−8 Pa in the SRF cavities within a very limited lengthof only 75 cm, ensuring a beam aperture greater than
40 mm. The properties of pumps we used for the DPS
are summarized in Fig. 1. Optimizations of the design
were performed with Molﬂow+2) . We measured the pressures of three stages in a prototype DPS when we leakedN2 and H2 with three diﬀerent leak rates, respectively.
The observed pressures are in good agreement with thecalculated ones (Fig. 2). The DPS also has fast closing gate valve (Series 75.2; VAT Group AG) responses
within 10 ms after receiving the signal of the pressure riseof three distributed cold-cathode gauges to protect theSRF systems from unexpected vacuum breaks. Compact
electrostatic particle suppressors (EPSs) were equipped
at the inside of the ﬁrst-stage chambers of the DPSs tosuppress the scattering of particles and reduce possibili-Fig. 1. Design of three-stages DPS and pump properties.
∗1∗2

RIKEN Nishina Center
Sumitomo Heavy Industries Accelerator Science Ltd.

Fig. 2. Pressure distributions for N2 and H2 leakage.

Fig. 3. Photograph of the DPS and the EPS.

ties to transport particles to the SRF cavities. The EPSconsists of two electrodes, each of which consists of 6
stainless-steel bars, as shown in Fig. 3. Some particle
tests with the EPS in air and vacuum were performed
with a vacuum particle sensor (VACUUM PARTICLESENSOR; Wexx Co., Ltd). Ceramic and metal particles were artiﬁcially generated by scraping blocks. The
counts were signiﬁcantly reduced when we applied a highvoltage on the electrodes. The vacuum in the beamlines
becomes an ionizing environment due to the energetic
heavy ions passing during the operation. We expect thatthe EPS can suppress particle transport to the SRF cavities.
All components (chambers, pumps, valves, vacuum
gauges, etc.) were cleaned and assembled in a clean
room of ISO class 1. The installation of the pair DPSs
was completed in December 2019. Some pumps areequipped in the horizontal direction to prevent particle falls (Fig. 3). We already conﬁrmed that the desiredpressure reductions were successfully achieved, and actual operations will start soon.
References

1) N. Sakamoto et al., Proc. LINAC’18, Beijing, WE2A03(2017).
2) Molflow+, http://molflow.web.cern.ch/ .
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