Performance of the Solid-state Neutral Particle Analyzer Array on the National Spherical Torus Experiment
Authors: D. Liu, W.W. Heidbrink, D.S. Darrow, A.L. Roquemore, S.S. Medley, and K. Shinohara
Date of PPPL Report: June 2006
Submitted to: Review of Scientific Instruments
Presented at the Sixteenth Conference on High Temperature Plasma Diagnostics, 7 - 11 May 2006, Williamsburg, Virginia USA.
The Solid State Neutral Particle Analyzer (SSNPA) array on the National Spherical Torus Experiment (NSTX) consists of four chords with tangency radii 60, 90, 100 and 120 cm that view across the three co-injection neutral beam lines. Each chord utilizes a silicon photodiode that is coupled to fast digitizers to measure the energy distribution of charge exchange fast neutral particles (30~100 keV). By the end of the NSTX 2005 experimental campaign, the electromagnetic noise in the SSNPA was reduced by half and reasonable signals were obtained with good electromagnetic shielding, fast digitization of raw signals, software-based pulse height analysis and pulse shape discrimination. Energy resolution of ~10 keV and time resolution of 2 ms have been achieved. Temporal evolutions of energetic neutral flux obtained with the SSNPA are in good agreement with those obtained with the E||B type Neutral Particle Analyzer (NPA). With these improvements, the SSNPA can be used to study magnetohydrodynamic instabilities and fast ion redistribution. Example data from plasma discharges will be presented along with the noise reduction techniques and post-shot pulse height analysis (PHA) methods.