Modelling of plasma facing components thermal response to runaway electron impact

The achievement of limitless clean energy production by means of nuclear fusion has fascinated the scientific community for more than half a century. Decades of combined theoretical and experimental work have been dedicated to confine a plasma in which the fusion reactions are self-sustained; facing and suddenly overcoming some of the most arduous challenges ever taken on. With the upcoming realization of the ITER project, mankind has never been so close to succeed, despite many technical and engineering problems awaiting to be solved. Among those, runaway electrons represent one of the biggest threats to the integrity of the plasma facing components of tokamak fusion devices. In fact, these high energy electron beams, generated in the course of the evolution of plasma instabilities, eventually impact the containing vessel leading to extreme heating and strong temperature gradients. The kinetic energy of runaway electrons is large enough to guarantee deep penetration and volumetric energy deposition. Deep melting, splashing or explosive material detachment might follow, seriously compromising the life-time and power handling capabilities of these sensitive components. In this presentation, the development of a rigorous flexible tool to simulate, through MonteCarlo (MC) transport methods, runaway electron energy deposition inside condensed matter is discussed. The physics involved in describing the interactions of primary and secondary particles is intricate and therefore deserves a proper validation activity against the most accurate experimental data to avoid inaccuracies. In parallel to the benchmarking tests, applications to real case scenarios are presented, which concern the controlled exposure of a graphite dome to runaway electrons produced in the DIII-D tokamak. In particular, the consistency of the predicted temperature profile and vaporization losses with experimental observations is reported.