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P: Fachverband Plasmaphysik
P 5: Poster I
P 5.43: Poster
Tuesday, August 31, 2021, 14:00–16:00, P
Modeling the beam emission Balmer-α spectrum in neutral beam heated plasmas at Wendelstein 7-X — •Sebastian Bannmann1, Oliver Ford1, Udo Höfel1, Peter Poloskei1, Jakob Svensson1, Benedikt Geiger2, and Robert Wolf1 — 1IPP Greifswald — 2University of Wisconsin, Madison, US
The optimized stellarator Wendelstein 7-X (W7-X) is equipped with a neutral beam injection (NBI) system. Knowledge about the particle and heat deposition of the beam in NBI shots is essential for further plasma physics analysis. The deposition depends on the beam and plasma parameters and information can be provided by measuring the Balmer-α light emitted by excited beam and halo particles. As the whole spectrum is too complex to be unambiguously fitted, a modular Bayesian inference network called Minerva is used. This requires implementing a detailed forward model with which one can infer beam and plasma parameters from the measured spectra. Existing modeling tools deploy Monte-Carlo techniques which is not feasible to use in combination with a Bayesian inference framework. The presented work focuses on the modeling of the neutral beam halo including collisional radiative processes to determine the fraction of neutrals in excited states. It is shown that the ballistic transport of halo particles can be described by a steady-state charge exchange diffusion equation. The possibility of inferring ion temperature profiles from the halo Balmer-α emission is investigated.