抄録
In fusion experimental devices and fusion reactors, helium particles bombard the plasma-facing surfaces and may result in various effects. This helium to plasma-surface interaction will be an important issue in developing plasma-facing materials and maintaining plasma control. In this article, studies on the helium plasma-surface interaction in TRIAM-1M and LHD, considered especially from the view point of material science, will be reviewed. It was clear from the TRIAM-1M experiments that metals facing the plasma were damaged by relatively high energy charge exchange neutrals of helium. Formation of fine dense He bubbles was remarkable. It is considered that the affect of the damage on the surface properties is dramatic. For LHD experiments, heavy damage by divertor plasma deserves particular mentions. In spite of the very low energy of helium ions, surface erosion by blistering occurred. This phenomenon is important in the evaluation of lifetime of the divertor plates and contamination of the main plasma. Helium glow discharge cleaning in LHD caused very heavy irradiation effects in the sub-surface region. Though establishment of a fundamental understanding of helium-material interaction is in progress by theoretical and by experimental studies using small scale ion injectors, the high temperature plasma confinement devices play a significant role in foreseeing the phenomena of plasma-surface interaction under the complex conditions of reactors.
