L. Simons, M. Hoppe, U. Sheikh, J. Decker, B. Duval, J. Cerovsky, O. Ficker & E. Macusova
February 1st, 2023

Fast populations of electrons with energies > 1MeV observed in present day tokamaks are expected to occur in ITER [1, 2]. These Runaway Electrons (RE) are accelerated to relativistic speeds by the loop voltage in low density plasmas because the collisional drag force decreases with increasing velocity. If unmitigated, REs have the potential to penetrate the vacuum vessel, causing significant damage that may halt operation [3]. In order to mitigate RE damage and explore scenarios with ”benign termination” [4], it is necessary to both model and measure REs to understand the physics which governs their generation, confinement and transport.

In this talk, the design and modelling of a Hard X-Ray spectrometer for the Tokamak `a Configuration Variable (TCV) is presented. The use of
scintillator based detectors is explored, including the need for calibration, shielding, collimation, signal processing and modelling to recover information about the initial electron energy distribution. Simulations of photon transport in the detector geometry with Geant4 are used to build a synthetic detector response function which is demonstrated to provide useful reconstructions of the photon energy distribution from measured spectra.

References
[1] A. H. Boozer. Runaway electrons and ITER. Nuclear Fusion, 57(5), 2017.
[2] B. Esposito, R. Martin Solis, P. Van Belle, O. N. Jarvis, F. B. Marcus, G. Sadler, R. Sanchez, B. Fischer, P. Froissard, J. M. Adams, E. Cecil,
and N. Watkins. Runaway electron measurements in the JET tokamak. Plasma Physics and Controlled Fusion, 38(12):2035–2049, 1996.
[3] R. A. Pitts, S. Carpentier, F. Escourbiac, T. Hirai, V. Komarov, A. S. Kukushkin, S. Lisgo, A. Loarte, M. Merola, R. Mitteau, A. R. Raffray,
M. Shimada, and P. C. Stangeby. Physics basis and design of the ITER plasma-facing components. Journal of Nuclear Materials, 415(1
SUPPL):S957–S964, 2011.
[4] U. Sheikh, J. Decker, G. Papp, B. P. Duval, S. Coda, J. Cazabonne, and L. Simons. Runaway Electron Studies on TCV, 2022.