4D and 5D phase-space tomography using slowing-down physics regularization

• Published in: Nuclear fusion 2023-07, Vol.63 (7), p.76016
• Main Authors: Schmidt, B.S., Salewski, M., Moseev, D., Baquero-Ruiz, M., Hansen, P.C., Eriksson, J., Ford, O., Gorini, G., Järleblad, H., Kazakov, Ye O., Kulla, D., Lazerson, S., Mencke, J.E., Mykytchuk, D., Nocente, M., Poloskei, P., Rud, M., Snicker, A., Stagner, L., Äkäslompolo, S.
• Format: Article
• Language: English
• Subjects: fast ions; NBI; slowing-down; stellarator; Tokamak; tomography
• ISSN: 0029-5515; 1741-4326; 1741-4326
• DOI: 10.1088/1741-4326/acd6a6

We compute reconstructions of 4D and 5D fast-ion phase-space distribution functions in fusion plasmas from synthetic projections of these functions. The fast-ion phase-space distribution functions originating from neutral beam injection (NBI) at TCV and Wendelstein 7-X (W7-X) at full, half, and one-third injection energies can be distinguished and particle densities of each component inferred based on 20 synthetic spectra of projected velocities at TCV and 680 at W7-X. Further, we demonstrate that an expansion into a basis of slowing-down distribution functions is equivalent to regularization using slowing-down physics as prior information. Using this technique in a Tikhonov formulation, we infer the particle density fractions for each NBI energy for each NBI beam from synthetic measurements, resulting in six unknowns at TCV and 24 unknowns at W7-X. Additionally, we show that installing 40 LOS in each of 17 ports at W7-X, providing full beam coverage and almost full angle coverage, produces the highest quality reconstructions.