Description
We present a study on the dynamics of runaway electrons (RE) in the WEST (Tungsten Environment in Steady State Tokamak) [1] tokamak, where up to 400 milliseconds RE beam have been achieved in post-disruption mode. The analysis includes discharges from experiments on the RE benign termination as well as RE impact on the W-tiles of the inner bumper.
The work is based on experimental synchrotron spectral data collected by the Runaway Electron Imaging and Spectroscopy diagnostic (REIS) [2] in the range 520-4000 nm and images obtained by visible and infrared cameras. A method based on the comparison between experimental and simulated data is adopted to infer the RE number, pitch angle, energy and radial profile. The simulations are carried out by means of the synthetic synchrotron radiation diagnostic tool SOFT (Synchrotron-detecting Orbit Following Toolkit) [3]. The numerical magnetic fields (radial, vertical and toroidal components) as determined by the equilibrium reconstruction are provided in input to SOFT together with the geometrical position and dimensions of the detectors, viewing direction, field of view and spectral range.
The inferred maximum RE energy and pitch angle are also compared with the results of simulations based on a RE test particle model [4].
[1] J. Bucalossi et al., The WEST project: Testing ITER divertor high heat flux component technology in a steady state tokamak environment, Fusion Engineering and Design, 89 (2014) 907.
[2] G. Ghillardi et al., Study of runaway electron dynamics in FTU using synchrotron spectra and imaging measurements, Plasma Physics and Controlled Fusion 67 (2025) 055029.
[3] M. Hoppe et al., SOFT: a synthetic synchrotron diagnostic for runaway electrons, Nuclear Fusion 58 (2018) 026032.
[4] J.R. Martin-Solis et al., Momentum–space structure of relativistic runaway electrons, Phys. Plasmas 5 (1998) 2370