Tomographic reconstruction of the runaway distribution function in TCV using multispectral synchrotron images
Journal article, 2021

Synchrotron radiation observed in a quiescent Tokamak Configuration Variable (TCV) runaway discharge is studied using filtered camera images targeting three distinct wavelength intervals. Through the tomographic simultaneous algebraic reconstruction technique (SART) procedure the high momentum, high pitch angle part of the spatial and momentum distribution of these relativistic particles is reconstructed. Experimental estimates of the distribution are important for verification and refinement of formation-, decay- and transport-models underlying runaway avoidance and mitigation strategy design. Using a test distribution it is demonstrated that the inversion procedure provides estimates accurate to within a few tens of percent in the region of phase-space contributing most to the synchrotron image. We find that combining images filtered around different parts of the emission spectrum widens the probed part of momentum-space and reduces reconstruction errors. Next, the SART algorithm is used to obtain information on the spatiotemporal runaway momentum distribution in a selected TCV discharge. The momentum distribution is found to relax towards an avalanche-like exponentially decaying profile. Anomalously high pitch angles and a radial profile increasing towards the edge are found for the most strongly emitting particles in the distribution.Pitch angle scattering by toroidal magnetic field ripple is consistent with this picture. An alternative explanation is the presence of high frequency instabilities in combination with the formation of a runaway shell at the edge of the plasma.

tokamak

2D spectroscopy

tomographic inversion

TCV

synchrotron radiation

runaway electrons

SOFT

Author

T. A. Wijkamp

Eindhoven University of Technology

Dutch Institute for Fundamental Energy Research (DIFFER)

A. Perek

Dutch Institute for Fundamental Energy Research (DIFFER)

J. Decker

Swiss Federal Institute of Technology in Lausanne (EPFL)

B. Duval

Swiss Federal Institute of Technology in Lausanne (EPFL)

Mathias Hoppe

Subatomic, High Energy and Plasma Physics PP

G. Papp

Max Planck Society

U. Sheikh

Swiss Federal Institute of Technology in Lausanne (EPFL)

I. Classen

Dutch Institute for Fundamental Energy Research (DIFFER)

R. J.E. Jaspers

Eindhoven University of Technology

Nuclear Fusion

0029-5515 (ISSN)

Vol. 61 4 046044

Subject Categories

Probability Theory and Statistics

Computer Vision and Robotics (Autonomous Systems)

Fusion, Plasma and Space Physics

DOI

10.1088/1741-4326/abe8af

More information

Latest update

4/26/2021