Beam ion transport from neutron emissivity measurement in deuterium neutral beam-heated deuterium plasmas of the HL-2A tokamak

An experiment at the HL-2A tokamak with a high-energy deuterium neutral beam (NB) injection (30 keV, about 0.6 MW) was performed. The emission of d-d fusion neutrons dominated by beam-plasmas reactions when the deuterium NB was injected into the deuterium target plasma was observed by means of a 235U fission chamber. To obtain information on NB deposition and the slowing down of beam ions in HL-2A plasmas, a very short-pulse deuterium NB injection, or the so-called 'blip' injection, was performed into MHD-quiescent Ohmic deuterium plasmas. Analysis of neutron decay following the NB 'blip' injection indicates that tangentially injected beam ions are well confined, slowing down classically in the HL-2A. In contrast to the MHD-quiescent plasma, anomalous losses of beam ions were observed when tearing mode instabilities were present. (authors)