Runaway electron velocity-space observation regions of bremsstrahlung hard X-ray spectroscopy

TL;DR

This paper develops a method to connect bremsstrahlung X-ray spectra with the velocity-space distribution of runaway electrons in fusion plasmas, enabling detailed diagnostics of their dynamics during disruptions.

Contribution

It introduces weight functions that link bremsstrahlung emission spectra to specific regions in runaway electron velocity space, facilitating 2D energy-pitch reconstruction.

Findings

Weight functions successfully map bremsstrahlung spectra to RE velocity regions

Application to JET diagnostics reveals velocity-space sensitivity

Method enhances understanding of RE beam dynamics during disruptions

Abstract

The reconstruction of the distribution function of runaway electrons (RE) in magnetically confined fusion plasmas gives insights on the runaway electron beam dynamics during plasma disruptions. In view of enabling a two-dimensional, energy-pitch reconstruction of the RE velocity space, in this work we present a calculation of the weight functions for the bremsstrahlung emission by the REs. The weight functions allow bridging the bremsstrahlung spectrum with the RE velocity space, as they tell the region of the velocity space that contributes to a particular spectral measurement. The results are applied to investigate the RE velocity-space sensitivity of the hard X-ray diagnostic installed at the Joint European Torus.