Investigation of the effective confinement time of energetic ions in LHD by using neutron measurement and simulation

Enhancement of the plasma heating efficiency is one of the most important issue for magnetically confined fusion devices. In general, the plasma heating in fusion devices is achieved by the kinetic energy transfer from fast ions, which are generated by the neutral beam (NB) injection, the radio frequency waves, and the fusion reactions, to bulk plasmas through Coulomb collision. To obtain the high efficiency of the plasma heating, fast ions should be confined in plasmas until its kinetic energy is transferred sufficiently. Unfortunately, however, the fast ion confinement often degrades due to several transport mechanisms. For this reason, there are numerous researches, which have performed to clarify the fast ion transport mechanisms.