Neutral particle analyzer diagnostic on the National Spherical Torus Experiment

The neutral particle analyzer (NPA) diagnostic on the National Spherical Torus Experiment (NSTX) utilizes a PPPL-designed EIIB spectrometer that measures the energy spectra of minority hydrogen and bulk deuterium species simultaneously with 39 energy channels per mass specie and a time resolution of 1 ms . The calibrated energy range is E=0.5–150 keV and the energy resolution varies from ΔE/E=3%–7% over the surface of the microchannel plate detector. The NPA measures Maxwellian spectra of residual hydrogen to obtain ion temperatures and measures the energetic ion spectra produced by injection of up to 100 keV deuterium neutral beams into deuterium plasmas. The NPA views across the coinjection paths of the three neutral beam sources on NSTX which localizes the measured charge exchange effux to the intersection region. The incorporation of horizontal scanning for the NPA over a sightline tangency range of R tan =125–−75 cm has enabled measurement of the anisotropic energy distribution of the beam ions. Vertical scanning allows measurements to be made from the horizontal midplane through an angle of 26° downward. A description of the NPA diagnostic on NSTX will be presented along with illustrations of measurement capability.