Three-dimensional proton trajectory analyses and simulation of neutral particle transport in an ICRF heated long pulse discharge on the large helical device

A three-dimensional neutral particle transport simulation code is applied to identify a source of the hydrogen outgas in a LHD long pulse discharge by ICRF heating. Radiation collapse induced by uncontrollable plasma density rise terminated the long pulse discharge. Toroidally non-uniform increases in the Hα emission and divertor temperature were observed. A CCD camera detected local heating of a vertically installed divertor plate, which is consistent with the strike points of the trajectories of protons accelerated by ICRF waves. The neutral particle transport simulation with the proton trajectory analyses shows that outgas from the divertor plates heated by the protons is necessary for explaining the observed toroidal non-uniform distribution of the Hα emission in the long pulse discharge.