Transient heating effects on tungsten: Ablation of Be layers and enhanced fuzz growth

A pulsed laser in the PISCES-B facility is used to simulate transient heating events such as ELMs and disruptions on W. The first study of enhanced nano-scale W tendril growth (“fuzz”) due to cyclic fast transient heating of W exposed to low energy (EHe+ ∼ 30 eV) He+ ions is presented. Fuzz due to transient heating is up to ∼10× thicker than the steady state fuzz thickness with no laser heating. A general thermal activation model yields higher values for the activation energy and pre-exponential factor than previously reported in steady state experiments with EHe+ ∼ 60 eV. Transient heating of W exposed to D plasma with Be seeding shows that the removal threshold of Be follows simple energy considerations based on the heat of formation of Be.