A synthetic diagnostic for Hard X-ray signal levels from runaway electrons on SPARC

The SPARC tokamak [1] will be equipped with a hard X-ray (HXR) monitor system [2]. It will measure the bremsstrahlung photons emitted by runaway electron (REs) with energy in excess of 100 keV that interact with plasma ions and the tokamak limiter. The main mission of this diagnostic is to detect the formation of ramp-up REs and inform the plasma control system on the need to ramp down the discharge and protect the structural integrity of the machine.

In this work we present a workflow to estimate the signal levels of HXR on SPARC. The RE population and the RE losses on the first wall will be studied using 0D calculations, such as the STREAM code [3]. Higher fidelity approaches will also be investigated, such as evolving the RE distribution function with fluid-kinetic models implemented in the DREAM code [4], and studying the location of the RE losses with the HEAT code [5]. Finally we will use radiation transport codes, such as the OpenMC code [6], to evaluate the HXR transport to the detector position. This workflow informs the refinement of control-oriented models used to design and test the real-time detection and response to REs in the ramp-up. It is also used to scope the HXR monitor as a diagnosis tool for post-disruption REs.

Supported by Commonwealth Fusion Systems.

[1] A. J. Creely et al., JPP 86.5 (2020)

[2] E. Panontin et al. RSI (2024)

[3] M. Hoppe et al., JPP, 88.3 (2022)

[4] M. Hoppe et al., Comput. Phys. Commun., 268 (2021)

[5] T. Looby et al., NF 62.10 (2022)

[6] P. Romano et al., Ann. Nucl. En. 82 (2015)