Edge-localized-mode heat load effects on plasma-facing materials studied using runaway electrons in the Damavand tokamak

Edge localized modes (ELMs) and runaway electrons (REs) pose significant challenges for all tokamak devices. Both phenomena act as potent heat sources, potentially shortening the lifespan of plasma-facing materials (PFMs). These thermal loads can manifest in various detrimental effects, including melting, sputtering, cracking, blistering, and other forms of material degradation. While the ELMs are an intrinsic feature of H-mode operation in tokamaks, runaway electrons pose a potential threat across all tokamak device scales. In devices such as ITER, even with mitigation strategies, the ELMs can still impose considerable heat loads on the PFMs, reaching levels of approximately 1MJ/m^{2}. Various methods exist to experimentally simulate the heat load effects of ELMs on PFMs. In this study, the thermal loads from runaway electrons in small-scale tokamaks are considered for this purpose. The presence of small-scale tokamaks, exemplified by the Damavand experiment, facilitates the investigation of runaway electron energy deposition. Analysis of the experimental data indicates that the RE populations generated by plasma instabilities within the Damavand tokamak discharges exhibit heat densities on the order of MJ/m^{2} to 1cm^{2} area PFMs. Furthermore, considering an average RE energy of 1 MeV and the prevailing discharge current, calculations indicate that the average total energy of the REs population per discharge is approximately 1 kJ, which is subsequently deposited on the tokamak limiter. Considering the limiter's surface area and assuming that only 40% of the RE energy is transferred to it, the calculated heat load density reaches the order of MJ/m^{2}, comparable to that observed during the ELM events in large-scale fusion devices. This correspondence in heat flux levels enables the Damavand tokamak to investigate material behavior under intense thermal loads, offering valuable insights into the effects of the ELMs on the performance and durability of PFMs in large-scale tokamaks.