Calorimetry probe for runaway electron heat load measurement at COMPASS.

Runaway electrons, accelerated in a tokamak discharge to high energies (tens of MeV), can cause serious damage to plasma facing components. Therefore, it is important to develop effective mitigation strategies to reduce the risk of tokamak damage. To study the effects of various mitigation strategies, a dedicated diagnostic, the calorimetry probe, was developed at the COMPASS tokamak. This probe successfully measured the heat loads caused by runaway electrons directly, using a set of temperature sensors embedded in a graphite body. Deposited energy measured by the probe ranged from a few hundred joules up to (15 ± 1) kJ, while the mean deposited energy was (4.5 ± 1.1) kJ. The design of the probe and the initial results from 250 discharges covering four experimental campaigns dedicated to runaway electron studies (2019-2021) are presented in this article.