Experimental investigation of ELM-like transient heat loads on plasma-facing materials using runaway electrons

Edge-localized modes (ELMs) and runaway electrons (REs) are among the most critical transient heat sources responsible for degradation of plasma-facing materials (PFMs) in tokamaks. Small-scale tokamaks, such as Damavand, provide a practical platform for investigating ELM-like thermo-mechanical effects under RE-dominated regimes. RE-induced heat loads in Damavand typically result in deposited energy densities of approximately 0.1–0.3 MJ/m 2 per discharge, pulse durations of 65–250 µs, and penetration depths up to ∼ 400 µm, which are comparable to the characteristic thermal loading conditions associated with ELMs in large-scale tokamaks. To experimentally assess this capability, SS316L stainless steel was selected as a PFM because it enables clear observation of progressive thermo-mechanical degradation under experimentally achievable transient heat loads. Samples were exposed to 20 RE-dominated discharges, corresponding to an estimated cumulative deposited energy density of approximately 2–6 MJ/m 2 . SEM, EDX, and XRD were performed before and after exposure to investigate the effects of repeated transient thermal loading. SEM observations revealed significant surface degradation, including crack formation, blistering, melting, and molten layer movement. EDX analysis detected no additional elements within the detection capability of the technique after RE exposure. XRD analysis revealed increased lattice spacing and peak broadening, indicating modifications of the lattice structure following transient thermal loading. The agreement between the SEM, EDX, and XRD observations indicates that RE-induced transient heat loads in small-scale tokamaks can generate ELM-like thermo-mechanical degradation features in PFMs. Overall, the results demonstrate the capability of RE-dominated small tokamaks, particularly Damavand, for studying ELM-like degradation mechanisms and provide experimental insight into the transient thermal response of plasma-facing materials through a cost-effective experimental approach.