Analysis of Energetic Particle Confinement in LHD Using Neutron Measurement and Simulation Codes

The fast ion confinement time in the Large Helical Device (LHD) is investigated by using the neutron measurement and simulations. To estimate the fast ion confinement time, a series of short pulse neutral beam (NB) injection experiments have been performed. Additionally, the NB heating simulation code, CONV_FIT3D, has been extended to estimate the neutron emission rate in LHD. We estimate the fast ion confinement time from the differences between the measured and the simulated neutron decay times after the NB is turned off. It is found that the fast ion confinement time of three tangential NBs have similar values τc ∼ 0.5 sec and the confinement time of the perpendicular NB is approximately τc ∼ 0.06 sec. Additionally, by using the confinement time and the ion ratio data estimated from the simulation result, we can obtain a simulation result similar to the measured data.