Study of high energy particles produced by ICRF heating in Heliotron-E

Abstract

In ion cyclotron range of frequency (ICRF) heating experiments in Heliotron-E, high energy particle production and confinement were studied. The high energy tail (up to 100 keV) formation of minority protons was clearly observed in a low density plasma experiment. The high energy tail below several tens of kiloelectronvolts was formed within 1 ms. The higher energy flux above this range developed within about 10 ms. The flux decay time after termination of the ICRF pulse was short compared with the values expected from the collisional process. The orbit loss of the accelerated particles is important for estimating the ICRF heating, particularly in helical confinement devices. To analyse the heating and orbit loss mechanism, a Monte Carlo code was used with an ICRF wave acceleration term. The time evolution of the tail formation and its decay resulting from the calculations agreed with the experimental ones. From this analysis, it is clear that the high energy particle production in ICRF experiments in helical confinement systems can be described by RF acceleration, collisional relaxation and orbit loss processes, and also that the orbit loss is not negligible in the ICRF heating of the low density plasmas of Heliotron-E