A Calculation of the Distribution Function of ICRF Heated Plasma in LHD using a Bounce-Averaged Fokker-Planck Equation

High-energy ions produced by the ion cyclotron range of frequency (ICRF) heating were observed on the Large Helical Device (LHD). The dependence of the count number of high-energy particles on pitch-angle was studied using the time-of-flight neutral particle analyzer (TOF-NPA) in the LHD. The angle of the line-of-sight was scanned at five successive discharges sustained by ICRF heating only. A unique "rabbit-ear" structure with a large population of high-energy ions at a certain pitch-angle, was observed. A bounce-averaged Fokker-Planck equation was applied to the LHD plasma in the helical magnetic configuration in order to explain the structure of the measured distribution function. The calculation successfully reproduced the "rabbit-ear" structure.