High-definition velocity-space tomography of fast-ion dynamics. (19th August 2016)

• Record Type: Journal Article
• Authors: Salewski, M.; Geiger, B.; Jacobsen, A.S.; Hansen, P.C.; Heidbrink, W.W.; Korsholm, S.B.; Leipold, F.; Madsen, J.; Moseev, D.; Nielsen, S.K.; Nocente, M.; Odstrčil, T.; Rasmussen, J.; Stagner, L.; Stejner, M.; Weiland, M.
• Other Names: collab.
• Is Part Of: Nuclear fusion. Volume 56:Number 10(2016:Oct.)
• Publication Date: 2016-08-19
• Subjects: fast ions -- tomography -- tokamaks -- sawteeth -- neutral beam injection -- fast-ion D-alpha spectroscopy; Nuclear fusion -- Periodicals; 621.48405
• DOI: 10.1088/0029-5515/56/10/106024
• Languages: English
• ISSNs: 0029-5515

Abstract

Abstract: Velocity-space tomography of the fast-ion distribution function in a fusion plasma is usually a photon-starved tomography method due to limited optical access and signal-to-noise ratio of fast-ion D α (FIDA) spectroscopy as well as the strive for high-resolution images. In high-definition tomography, prior information makes up for this lack of data. We restrict the target velocity space through the measured absence of FIDA light, impose phase-space densities to be non-negative, and encode the known geometry of neutral beam injection (NBI) sources. We further use a numerical simulation as prior information to reconstruct where in velocity space the measurements and the simulation disagree. This alternative approach is demonstrated for four-view as well as for two-view FIDA measurements. The high-definition tomography tools allow us to study fast ions in sawtoothing plasmas and the formation of NBI peaks at full, half and one-third energy by time-resolved tomographic movies.