Experimental check of deceleration of neutral beam-injected energetic ions in the HL-2A tokamak

Short pulses of a deuterium neutral beam (NB) with a duration of less than ∼5 ms were co-injected into magnetohydrodynamic (MHD)-quiescent ohmic deuterium plasmas of the HL-2A tokamak to study the variation of the slowing-down time in two different electron temperature environments. Analyses were made for the decay rate of D-D neutrons produced by beam-plasma interaction following NB turn-off, i.e., experimentally observed neutron decay rates were compared with those predicted by a classical slowing-down model. The results suggest the beam ions decelerate without significant loss in the HL-2A tokamak in round terms. When the critical energy for beam ions is higher than the beam injection energy, it seems that a small fraction of the beam ions is lost. (author)