Development of diagnostic beams for alpha particle measurement on ITER

A study is conducted of the feasibility of alpha particle measurement using a high energy diagnostic beam in combination with a neutral particle analyser for an ITER plasma. In order to measure alpha particles over an energy range of 0.5 to 3.5 MeV, the required beam energy is approximately 1 MeV for a He-3(0) beam and 3 MeV for a Li-6(0) beam, the beam current density being about 1 mA/cm(2) for both cases. Among the various methods of producing such a high energy neutral beam, the acceleration of negative ions is the most favourable. Recent results of relatively small scale experiments with these negative ion sources reveal that the required current density is now attainable. Technical problems as to how to scale the ion sources used on an ITER sized experiment are also discussed for these experiments.