Characteristics of fast ³He ion velocity distribution exciting ion cyclotron emission on JT-60U

Ion cyclotron emission (ICE) is probably excited by non-thermal ion velocity distribution. Identifying characteristics of the ion velocity distribution that excites the ICE can contribute to understanding its emission mechanism. The characteristics of fast helium-3 (³He) ion velocity distribution that excites ³He ICE [ICE(³He)] on JT-60U are investigated. First, fast deuterium ion distributions, which mainly contribute to deuterium-deuterium fusion reactions, are calculated with a fast ion orbit following Monte-Carlo code (OFMC code) under realistic conditions to evaluate birth spatial and velocity distributions of the ³He ions. Then, the fast ³He ion distributions are evaluated with the OFMC code using the birth distributions and compared between cases when the ICE(³He) is observed and not. The evaluated fast ³He ion distributions at the midplane edge of the plasma on the low field side have strong pitch-angle anisotropy in both cases. In the case with the ICE(³He) excitation, a relatively peaked bump-on tail structure in the energy direction is formed in the distributions. The formation of the relatively peaked bump-on tail structure is localized at the plasma edge on the low field side. On the other hand, the distributions at the plasma edge on the low field side have a broader structure in the energy direction in the case without the excitation. The comparison results show that the formation of the relatively peaked bump-on tail structure in the fast ³He ion distribution makes a key contribution to the excitation of the ICE(³He) on JT-60U.