Ⅱ-8. Accelerator

RIKEN Accel. Prog. Rep. 52 (2019)

Pressure measurement of plasma window with large diameter
N. Ikoma,∗1,∗2 Y. Miyake,∗1 M. Takahashi,∗1 H. Okuno,∗1 S. Namba,∗3 and T. Kikuchi∗4210

P1 [kPa]

The plasma window (PW),1) which separates a vacuum from an atmosphere by an arc plasma ﬁlling thedischarge channel, is a novel beam window technology. It has several applications in an accelerator system such as a gas charge stripper2,3) for a heavy ion
accelerator or a beam window for an accelerator-driven
subcritical reactor (ADS).4) In addition, a target system using PW has been proposed in the ImPACT Fujita program5) for the transmutation of long-lived ﬁssion products (LLFP) into a stable or short-lived nuclei. However, the small diameter of PW is a crucial
problem for these applications. The ﬁrst PW invented
by Hershcovitch,1) with an aperture of 2.36 mm, aimed
at electron beam welding in an atmosphere. However,the beam spot size in our intended case is several tensof millimeters or more. Therefore, to implement thePW in the accelerator system, its diameter needs tobe enlarged. Furthermore, an investigation of the relation between conﬁnement pressure and diameter isalso important to predict the performance of PW forvarious purposes. Therefore, we have developed a PW
with large diameter in reference to a PW designed by
Namba et al.6) In a previous study,7) we reported theperformance of a PW with a diameter of 10 mm. After that, we systematically measured the pressure byvarying the diameter from 6 to 20 mm. In this study,
the preliminary results of pressure measurement havebeen reported.
The experimental setup is shown in Fig. 1. Argon
gas was introduced from the upstream of the PW. It
was then exhausted by two mechanical booster pumps(Edwards, EH 500, the exhaust speed of each pump
was approximately 100 L/s). Three DC power sup-101

1000

∗1
∗2
∗3
∗4RIKEN Nishina Center
Department of Energy and Environment Science, Nagaoka
University of Technology
Graduate School of Engineering, Hiroshima University
Department of Nuclear System Safety Engineering, Nagaoka
University of Technology- 118 -1015Diameter [mm]2025Fig. 2. Dependence of P1 on the diameter of PW.

plies (TDK Lambda, ESS-400-37-2-D) were connectedin parallel between the cathode and anode, and an arc
current of 100 A was supplied. The discharge voltage
was monitored by a data logger (KEYENCE, NR-600).
The gas ﬂow rate was maintained at 20 L/min by themass ﬂow controller (MKS Instruments, 1579 A) andboth upstream and downstream pressures, P1 and P2 ,were measured.
Figure 2 shows the upstream pressure P1 on each diameter, which decreased with an increase in the diameter of PW. P2 was maintained at approximately 200 Pa
in each condition. These results will be compared withthose of an existing theoretical model (P1 ∝ 1/r2 )based on viscous laminar ﬂow.8,9) We will determine
a prediction model that can describe the conﬁnement
pressure in the PW with a large diameter.
This work was supported by RIKEN Junior Research Associate Program and funded by ImPACT
Program of Council for Science, Technology and Innovation (Cabinet Oﬃce, Government of Japan).
References

Fig. 1. Experimental setup.

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(2014).
4) S. Ben-Liang et al., Chin. Phys. C 38, 018201 (2014).
5) Impulsing Paradigm Change through Disruptive Technologies Program ImPACT, http://www.jst.go.jp/impact/en/index.html, accessed: January 21, 2019.
6) S. Namba et al., Rev. Sci. Instrum. 87, 083503 (2016).
7) N. Ikoma et al., RIKEN Accel. Prog. Rep. 51, 144(2018).
8) W. A. J. Vijvers et al., Phys. Plasmas 15, 093507 (2008).
9) S. Huang et al., Phys. Plasmas 21, 123511 (2014).