Speaker
Mr
Yusuke Kikuchi
(Japan)
Description
A magnetized coaxial plasma gun (MCPG) device has been developed for simulation experiments of transient heat and particle loads during type I edge localized modes (ELMs) predicted in ITER. The MCPG has been recently upgraded to increase surface absorbed energy density up to ~ 2 MJ/m^2 that makes it possible to investigate of tungsten (W) melting behaviors. In the experiment, mono-block W samples, to be used for the ITER divertor, were exposed to repetitive pulsed hydrogen plasmas with duration of ~ 0.2 ms, incident ion energy of ~ 50 eV, and surface absorbed energy density of ~ 0.7, 1.4, and 2 MJ/m^2. No melting occurred on the mono-block W surface at energy density of ~ 0.7 MJ/m^2, while major cracks were formed. Cracking and melting of the mono-block W surface were clearly observed at energy density of ~ 1.4 and 2 MJ/m^2. Micro-sized cracks were identified for energy density above the melting threshold.
It is considered that the micro-sized cracks were formed due to surface melting and resolidification in each plasma pulse. The mono-block W samples with pulsed plasma irradiation will be exposed to cyclic heat loads of ~ 20 MW/m^2 in an electron beam facility JEBIS at JAEA in order to investigate damage of ITER divertor materials under a combination of steady-state and transient heat loads.
Moreover, we introduce a new experiment using two MCPG devices to understand vapor shielding effects of a W surface under ELM-like pulsed plasma bombardment. The second plasmoid is applied with a variable delay time after the first plasmoid. A vapor cloud layer in front of the W surface produced by the first plasmoid irradiation could shield the second pulsed plasma load on the W surface. In this upgrade, weight loss measurements of W samples after pulsed plasma exposures became possible, which is a grate advantage for quantitative evaluation of vapor shielding effects on erosion of W.
Country or International Organization of Primary Author
Japan
Primary author
Mr
Yusuke Kikuchi
(Japan)
Co-authors
Mr
Daiki Iwamoto
(University of Hyogo)
Mr
Ikko Sakuma
(University of Hyogo)
Mr
Kyohei Shoda
(University of Hyogo)
Prof.
Masayoshi Nagata
(University of Hyogo)
Dr
Naoyuki Fukumoto
(University of Hyogo)
Dr
Satoshi Suzuki
(Japan Atomic Energy Agency)
Mr
Yoshinobu Kitagawa
(University of Hyogo)
Prof.
Yoshio Ueda
(Osaka University)
