Neutralization loss of high energy particles in the plasma boundary of LHD

Abstract

The neutralization loss of high-energy particles is studied by investigating the density dependence of the energetic neutral flux from large helical device plasmas of hydrogen and helium discharges. Clear difference between the density dependence of energetic particles originated from neutral beams and those produced by ion cyclotron radio frequency (ICRF) is observed. One of the causes of this difference is the spatial profiles of energetic particles characteristic to each heating scheme. The spatial distributions of H 0, He 0, He + are calculated as a function of the neutral source temperature entering across the Last Closed Flux Surface (LCFS) including six charge exchange processes, assuming a cylindrical geometry (ACHEN-Code). While the observed density dependence of energetic neutral flux escaping from ICRF-heated helium plasmas is well reproduced by the calculation with the incoming neutral temperature of about 10 eV, that from NBI-heated helium plasmas shows more modest dependence than the calculation.