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Abstract
Elemental tungsten, tungsten alloys, and boron nitride ceramics have been investigated for decades as highly resistant materials for the first walls of various types of fusion reactors and other high-energy-density applications. One of the key parameters of a particular refractory material is the damage threshold for energetic pulses of short-wavelength electromagnetic radiation, which represents a non-negligible fraction of the fusion plasma emission. Determining damage thresholds based on irreversible changes in surface morphology is often challenging because real samples typically have surfaces that differ significantly from a perfectly polished surface, where laser-induced morphology changes would ideally reveal threshold fluences. In practice, real samples or materials designed for the first walls of future reactors will rarely have perfectly smooth surfaces, whether by design (e.g., foams, sintered nano-powders, or nano-/micro-rod arrays) or due to manufacturing limitations and cost constraints, making it nearly impossible to reliably detect the early, subtle changes in surface morphology that form slightly above the threshold. In this article, we demonstrate that the fluence dependence of ion emissions induced by XUV laser radiation can be used to estimate the damage thresholds of several samples of elemental tungsten, tungsten/chromium alloy, and pyrolytic boron nitride. Analysis of the experimental results reveals better resistance (i.e., higher damage thresholds) of BN ceramics compared to W materials. Moreover, the threshold fluence values are in good agreement with computer simulations performed using the hybrid simulation code XTANT-3.