Initial neutral particle analyzer measurements of ion temperature in the National Spherical Torus Experiment

Abstract

The neutral particle analyzer (NPA) diagnostic on the National Spherical Torus Experiment (NSTX) utilizes a PPPL-designed E∥B spectrometer which measures the energy spectra of minority H and bulk D species simultaneously with 39 energy channels per mass species 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 thermal Maxwellian ion spectra to obtain line integrated ion temperatures, Ti. For line integral electron densities below neL∼3.5×1019 m−2, good agreement is observed between the line integrated NPA Ti and the central Ti(0) measured by the spatially localized charge exchange recombination spectroscopy (CHERS) diagnostic. However, with increasingly higher neL the NPA Ti falls below the central Ti(0) measured by CHERS because the charge exchange neutral emissivity weights the line integrated NPA measurement outboard of the plasma core. An analytic neutral analysis code, DOUBLE, has been applied to the NPA data to correct for this effect and restore agreement with Ti(0) measured by CHERS. A description of the NPA diagnostic on NSTX and initial ion temperature measurements along with an illustration of application of the DOUBLE code are presented.

Modeling fast-ion transport during toroidal Alfvén eigenmode avalanches in National Spherical Torus Experiment

“…NSTX has two NPA systems, the first being an "E ʈ B" system that can be scanned ͑on a shot-to-shot basis͒ in tangency radius ͑from looking co-nbi to ctr-nbi͒ as well as vertically, with high energy resolution. 105 The second is a fixed four-channel solid-state system with tangency radii of 60, 90, 100, and 120 cm. 106 The sFLIP detector is located on the outboard vacuum vessel wall at a major radius of 1.6 m, 0.14 m below the midplane 107 and measures the pitch and energy of the lost fast ions.…”

Wave Driven Fast Ion Loss in the National Spherical Torus Experiment

“…13). For these fishbones, large bursts in the Neutral Particle Analyzer (NPA) [57,58] signal have been observed coincident with the fishbone chirps on the Mirnov data. An example, from the latter half of the discharge shown in Fig.…”

Neutral Particle Analyzer Diagnostic on NSTX

“…In NB heated discharges, good agreement between CHERS and NPA minority H + T i (0) is also observed for electron densities up to n e (0) ~ 4x10 13 cm -3 . At higher densities, plasma opacity again interferes with the NPA measurements and it is necessary to correct for this effect with code modeling [11].…”

“…In deuterium neutral beam heated deuterium plasmas, the NPA measures temperatures, T i [11]. The deuterium thermal spectrum is useable only for energies up to ~ 5 keV because of spectrum contamination by deuterium beam slowing down ions.…”