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Medley, S. S.*; Andre, R.*; Bell, R. E.*; Darrow, D. S.*; Fredrickson, E. D.*; LeBlanc, B. P.*; Levinton, F. M.*; Menard, J. E.*; Stutman, D.*; Roquemore, A. L.*; et al.
Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03
The National Spherical Torus Experiment (NSTX) is particularly well suited to investigate fast-ion driven instabilities. These instabilities are observed in the wide range of frequency from 0 kHz to the ion cyclotron frequency. Two recently implemented diagnostics on NSTX, the Motional Stark Effect (MSE) and scintillator Fast Lost Ion Probe (sFLIP), facilitate separation of redistribution and loss effects. Outward redistribution of the core-peaked energetic beam ions modifies the beam-driven current profile and hence the core q-profile. For certain H-mode discharges where NPA measurements of the NB energetic ion spectra exhibit MHD-induced fast-ion depletion, the sFLIP data confirm the existence of an ion loss that occurs primarily for passing particles near the NB full injection energy. Observations and TRANSP simulations representing fast ion instability-induced redistribution/loss phenomena in NSTX are presented.
Liu, D.*; Heidbrink, W. W.*; Darrow, D. S.*; Roquemore, A. L.*; Medley, S. S.*; Shinohara, Koji
Review of Scientific Instruments, 77(10), p.10F113_1 - 10F113_4, 2006/10
Times Cited Count:19 Percentile:65.12(Instruments & Instrumentation)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 (30100keV). By the end of the NSTX 2005 run campaign, the 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 EB type Neutral Particle Analyzer. With these improvements, the SSNPA enables us to study MHD instabilities and fast ion redistribution.