Production of hot spot on a vertically installed divertor plate by ICRF heating in the large helical device

Plasma-wall interaction in long-pulse plasma discharges is an important issue for optimizing the first wall materials and divertor configurations for future nuclear fusion reactors. A visible charge coupled device (CCD) camera observed a hot spot on a vertically installed divertor plate in a long pulse discharge heated by ion cyclotron range of frequency (ICRF) in the large helical device (LHD). Two bright thin lines also appeared on a divertor leg. The analyses of the three-dimensional trajectory of protons accelerated by ICRF waves on two ion cyclotron resonance (ICR) layers in the plasma periphery can explain the observation of the CCD camera.