Impact of High Heat Fluxes from an Electrothermal Arc Plasma Source on Ultra-high Temperature Ceramics for Fusion Reactor Limiter Applications

Sacrificial limiters are a physical mitigation method that will likely be employed in a Fusion Pilot Plant (FPP) to protect the breeding blanket first wall from catastrophic damage caused by plasma transients. Ideal limiters would withstand heat and particle fluxes from both nominal operation and from unplanned plasma transients, be radiation resistant and chemically inert (avoiding tritium retention), and be composed of low- or mid-Z elements to prevent plasma contamination. Such requirements lead to the appeal of ultra-high temperature ceramics (UHTCs) which have favorable properties of both ceramics (high hardness and melting temperature) and metals (high electrical and thermal conductivity). In this work, initial testing of two UHTC compositions, ZrB₂ and TiB₂, is completed by analyzing the impact of several plasma discharges from a pulsed capillary plasma source on ZrB₂ and TiB₂ targets. Each plasma discharge lasts ~1 ms and generates 1 – 2 GW/m² heat fluxes due to impacts of ions, electrons, and neutrals onto the target material, simulating potential energy loadings of long ELMs from a future fusion device. This work aims to find an ELM magnitude threshold for UHTCs in an FPP and to compare UHTC surface evolution and failure response to other candidate materials.