High harmonics fast wave exper iments in the Lar ge Helical Device

With low order ICRF resonances, electron heating experiments using HHFW are tried in the LHD, and 2nd ion cyclotron heating and HHFW heating are observed at the same time. Even if single-pass-damping is less than a few %, direct electron heating is achieved, and effective heating region is outward from plasma core, and the region is close to simple 1-dimentional calculation result. Though direct electron heating region is not plasma core for low electron density (0.3 × 1019 m-3), heating efficiency is approximately 30%. Since HHFW can heat electrons for various electron densities (from 1018 to 1021 m-3) with multi-pass-damping, it is suggested that HHFW is important key role to heat Super Dense Core plasmas in the LHD [4].