24P061-P
Development of a magnetized plasma gun device
for ELM-like pulsed plasma irradiation
ELM様パルスプラズマ照射のための磁化プラズマガン装置の開発
Kyohei Shoda, Ikko Sakuma, Daiki Iwamoto, Yusuke Kikuchi,
Naoyuki Fukumoto and Masayoshi Nagata
生田 恭平, 佐久間 一行, 岩本 大希, 菊池 祐介, 福本 直之, 永田 正義
Graduate School of Engineering, University of Hyogo
2167 Shosha, Himeji, Hyogo 671-2280, Japan
兵庫県立大学 工学研究科 〒671-2280 兵庫県姫路市書写2167
The magnetized coaxial plasma gun (MCPG) device at University of Hyogo for simulation experiments oftype-I ELM heat loads has been upgraded to improve the performance. The characteristics of the upgraded
MCPG device have been investigated and compared with the previous one. The capacitor bank energy forthe power supply of the MCPG was increased from 24.5 kJ to 144 kJ. In the preliminary experiments, theplasmoid with duration of ~0.2 ms, the incident ion energy of ~40 eV, and the surface absorbed energy
density of ~2 MJ/m2 was successfully produced by the present MCPG device at the gun voltage of 6 kV.

1. Introduction
Thermal transient events such as type I
edge-localized modes (ELMs) and disruptions
remain a major concern to the lifetime ofplasma-facing components (PFCs) in ITER. It is
predicted that the heat load onto the PFCs during
type I ELMs in ITER is 0.2-2MJ/m2 with pulse
length of ~0.1-1ms [1]. Experimental investigationsof surface damage characteristics of candidate
materials for the PFCs under transient plasma loads
are highly required. However, it is difficult toachieve the predicted conditions in present tokamak
devices and linear divertor simulators.
We have investigated surface damage of thePFCs under transient heat loads by using amagnetized coaxial plasma gun (MCPG) at
University of Hyogo [2]. The stress-relieved W
samples were exposed to the repetitive pulsed

Target chamber
Outer electrodeplasma loads with duration of ~0.5 ms, incident ion
energy of ~30 eV, and surface absorbed energy
density of ~0.3-0.7 MJ/m2 [3]. No melting occurred
on a W surface exposed to a single plasma pulse of~0.7 MJ/m2, while cracks clearly appeared at theedge part of the W surface.
We have recently started to improve theperformance of the MCPG in order to investigate
melt layer dynamics of a W surface such as vapor
cloud formation [4]. In this study, we will show
characteristics of the upgraded MCPG device.
2. Experimental setup
Figure 1 shows a schematic view of the upgraded
MCPG produced in this study. The MCPG has
coaxial electrodes made of stainless steel 304. The
inner and outer electrodes are tapered for plasmacompression in order to increase the plasma density,

500 mmCapacitor bank
(10 kV, 2.9 mF, 144 kJ)+ GND
IgnitronCeramic

Fig. 1 Magnetized coaxial plasma gun deviceBulk W for tip of
inner electrode

Inner electrode (SUS304)
VPS W coating (0.2 mm)

Outer electrode (SUS304)

Fig. 2 Inner and outer electrodes in the MCPGdevice.

since the higher kinetic energy of the plasmoid
gives rise to a large energy deposition onto thetarget. The tip of the inner electrode is made of W
to suppress release of impurities from the innerelectrode during the discharge (Fig. 2). Two fastgas-puff valves are used to produce neutral gas forthe plasma production. The working gas ishydrogen in this study. A bias solenoid coil is
installed outside the outer electrode in order tomagnetize a plasmoid produced at the formation
region. A turbo molecular pump (150 L/s) isconnected to the bottom part of the MCPG. Thebase vacuum pressure is typically 1.0x10-7 Torr.
The energy density of ~ 0.7 MJ/m2 was observedin the former MCPG, in which the capacitor bank (1mF, 7 kV, 24.5 kJ) was used for the power supply[3]. The energy density has to be increased up to ~2 MJ/m2 in order to achieve droplet splashing of aW surface due to a pulsed plasma bombardment [4].
Then, a high energy density capacitor bank (2.88mF, 10 kV, 144 kJ) is prepared for the power supplyof the upgrade MCPG device. A target chamber isprepared for measurements of dynamics of plasma
material interactions due to pulsed plasma
irradiation.
3. Experimental results
The surface absorbed energy was measured withthe calorimeter by changing the gun voltage and thebias magnetic flux, as shown in Fig. 3. Here, thedischarge was unstable when the bias magnetic flux
was not applied. It is found that the energy density
increases when increasing the gun voltage (i.e.,capacitor bank energy). In addition, the peak energy
density appears at the bias magnetic flux of ~ 1
mWb. Thus, the energy density can be controlled by
the external bias magnetic flux. It is revealed thatthe higher energy density is observed at the lower
gun voltage of 6 kV in the upgraded MCPG. It is
expected that the energy density could exceed 2
MJ/m2, corresponding to the threshold of droplet
splashing of a W surface due to the pulsed plasma
bombardment [4].

Fig. 3 Dependences of the energy density of thepulsed plasma on the bias flux.

4. Summary
The characteristics of the modified MCPG device
were investigated and compared with the previous
one. The capacitor bank energy is increased from24.5 kJ to 144 kJ. In the preliminary experiments,
the plasmoid with duration of ~0.2 ms, incident ion
energy of ~ 40 eV, and the surface absorbed energy
density of ~2 MJ/m2 was successfully produced by
the present MCPG device at the gun voltage of 6kV.
Acknowledgments
This work is partially supported by a NIFS
collaboration
researchprogram(NIFS10KOAF001) .
References[1] G. Federici et al., Plasma Phys. Controlled Fusion 45(2003) 1523.
[2] Y. Kikuchi et al., IEEE Trans. Plasma Sci. 38 (2010)232.
[3] Y. Kikuchi et al., J. Nuc. Mater. 415 (2011) S55.
[4] N. Klimov et al., J. Nucl. Mater. 390-391 (2009)
7217.