In magnetic confinement fusion devices, plasma-facing materials are required to withstand severe high thermal loads, and their damage behavior significantly impacts the stability of the fusion plasma and the safety of the device. For the expected Type I edge-localized modes in future long-pulse steady-state fusion devices, the damage effects of multiple irradiations of transient thermal loads with low-medium energy density on tungsten materials are simulated using a coaxial plasma gun. At constant initial conditions (pulse frequency, gas-prefilled), the energy density is changed by altering the charging voltage to 0.1 MJ m−2 and 0.2 MJ m−2. Combining the discharge and plasma evolution characteristics of coaxial plasma gun, the temperature rise of the tungsten target under different heat loads and the damage effect on the tungsten material are studied. The results indicate that the types of W target damage mainly include roughening, micro-cracks, crack networks, and crack melting. The number of thermal shocks dominates heat accumulation and damage evolution. In the initial stage, microcracks dominate. During the intermediate stage, molten droplets play a role in repairing the crack network. In the later stage, molten droplets form a brittle recrystallization layer. Energy density determines the intensity of a single thermal shock. Under low-energy thermal shocks, micro-cracks caused by thermal stress are predominant, while high-energy thermal shocks promote crack propagation through grain loss and molten W droplets. The results of this simulation experiment provide valuable insights into the interaction mechanisms between low to medium energy density plasmas and first-wall materials in future tokamaks.
Response of tungsten surfaces to helium and hydrogen plasma exposure under ITER relevant steady state and repetitive transient conditions