Performance of Rhenium Using Low Energy Helium Ion Irradiation Under Extreme ConditionsJ.C. Johnson, T. Ray, J.K. Tripathi, and A. Hassanein*

Rhenium could be a promising candidate for plasma facing materials (PFMs) due to its high melting point, ductility, and sheer modulus. When compared to tungsten, the current leading candidate, rhenium has a higher density, more ductile, and low potential carbide formations as a potential contender for nuclear fusion applications. We studied nano tendril growth, commonly referred to as fuzz, caused by high temperature helium conglomeration on the sub-surface and compared it to that of tungsten. The performance testing of rhenium was conducted using low energy (100 eV) He⁺ ion irradiation as a function of (a) temperature (723 – 1323 K) using constant ion flux (3×10²⁰ ions m^-2 s^-1) and fluence (1. ×10²⁴ ions m^-2) and (b) ion fluence (1. ×10²⁴ – 1. ×10²⁵ ions m^-2) at a constant temperature of 1023 K. The testing temperatures were based on the evidence of “early stage” fuzz growth and maximum fuzz density (near zero optical reflectivity) conditions. During the study, at each step, we monitored the change in surface morphology, relative fuzz density, compositional analysis, and structural transformation using scanning electron microscopy (SEM), optical reflectivity, X-ray photoelectron spectroscopy, and X-ray diffraction characterizations. Rhenium, as tungsten, also shows weakness against helium ion exposures. This study highlighted significant impact on the ongoing fusion research, particularly in the basic understanding of fuzz formation, involved mechanisms, and potential mitigation methods.