Cracking and surface roughening of beryllium–tungsten alloy due to transient heating

A controlled beryllium–tungsten (Be–W) alloy was created in a beryllium-seeded deuterium plasma in the PISCES-B facility and irradiated by a pulsed laser in order to investigate how transient surface heating from plasma instabilities will affect the performance of mixed materials in ITER. Standardized wavelength dispersive x-ray spectroscopy was used to measure the depth profiles of beryllium and tungsten atomic concentrations, revealing beryllium penetration of ∼100 μ m in ITER comparable grade tungsten with 5000 s of plasma exposure at 1123 K and ion flux 8 × 10²² m⁻² s⁻¹. The deep Be penetration into W is a concern for the lifetime of the ITER divertor, which may form mixed Be–W material. Pulsed laser heating was used to investigate the thermo-mechanical response of Be–W alloy and pure W using temporal shape mimicking that expected for edge-localized modes in ITER, with up to 1.9 MJ m⁻² of absorbed energy density. Transient heating creates a lower surface roughness than pure W, but cracks appear in the alloy layer surface at lower absorbed energy density and lower pulse number. (paper)