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DOE OSTI · 1651250

Resolving the fast ion distribution from imaging neutral particle analyzer measurements

Du, X. D.·Van Zeeland, M. A.·Heidbrink, W. W.·Stagner, L.·Wingen, A.·Lin, D.·Collins, C. S.
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Abstract

A recently developed imaging neutral particle analyzer (INPA) on the DIII-D tokamak (Du 2018 Nucl. Fusion 58 082006) enables fast ion velocity-space tomography of high fidelity at the interrogated phase space. To accomplish this, the spatial and energy depending fast ( E < 80 keV) neutral flux towards the INPA stripping foils is calculated with FIDASIM and a newly developed code INPASIM simulates the INPA instrumental response to this neutral flux. Included in INPASIM is the neutral-foil interaction, the Larmor orbit tracing between the foil and the phosphor, the phosphor response to the incident ion flux as well as camera focusing. Benefiting from heavy, localized velocity-space weights and excellent signal to noise, computed tomography using the Ridge regression method is able to successfully reconstruct fine-scale velocity-space structures produced by multiple neutral beams separated by as small as ~3 keV in tests. Applying the inversion method to a sawtooth crash event reveals a significant profile flattening of confined passing particles across q = 1 flux surface, as well as a redistribution of fast ions into the trapped orbits at the plasma edge close to the last closed flux surface.

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70 PLASMA PHYSICS AND FUSION TECHNOLOGYfast ionfast ion, tomography, sawtoothsawtoothtomography

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Du, X. D., Van Zeeland, M. A., Heidbrink, W. W., Stagner, L., Wingen, A., Lin, D., Collins, C. S.. 2020-08-25. Resolving the fast ion distribution from imaging neutral particle analyzer measurements. https://doi.org/10.1088/1741-4326%2Fab788f

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