Doppler tomography in fusion plasmas and astrophysics

TL;DR

Doppler tomography is a technique used in both astrophysics and fusion plasmas to image velocity distributions of emitters, revealing flow structures and matching simulations, with potential for further insights.

Contribution

This paper compares astrophysical and fusion plasma Doppler tomography, discussing achievements, limitations, and the potential for cross-application insights.

Findings

Doppler tomography successfully images accretion discs in binaries.

Fusion plasma Doppler tomography reveals fast-ion velocity distributions.

Images match numerical simulations closely.

Abstract

Doppler tomography is a well-known method in astrophysics to image the accretion flow, often in the shape of thin discs, in compact binary stars. As accretion discs rotate, all emitted line radiation is Doppler-shifted. In fast-ion D-alpha (FIDA) spectroscopy measurements in magnetically confined plasma, the D-alpha-photons are likewise Doppler-shifted ultimately due to gyration of the fast ions. In either case, spectra of Doppler-shifted line emission are sensitive to the velocity distribution of the emitters. Astrophysical Doppler tomography has lead to images of accretion discs of binaries revealing bright spots, spiral structures, and flow patterns. Fusion plasma Doppler tomography has lead to an image of the fast-ion velocity distribution function in the tokamak ASDEX Upgrade. This image matched numerical simulations very well. Here we discuss achievements of the Doppler tomography approach, its promise and limits, analogies and differences in astrophysical and fusion plasma Doppler tomography, and what can be learned by comparison of these applications.