Testing tungsten plasma facing components in WEST and AUG tokamaks

Abstract Next step fusion devices will face unprecedented heat loads and particle fluence with thousands of hours of plasma exposure on plasma-facing components (PFCs) cumulated over the entire lifetime of the device. These components must guarantee an acceptable lifetime, reliable heat exhaust capabilities (10–15 MW m −2 power fluxes in steady state) and a high level of resilience after multiple thermal stresses generated by combined steady-state heat loads and transient events, such as edge localized modes (ELMs) or disruptions. An extensive tungsten (W) PFC testing work-programme has been conducted in the WEST (Tungsten Environment in Steady State Tokamak) and ASDEX Upgrade (AUG) tokamaks, taking advantage of key capabilities and strengths of the two machines. WEST is a superconducting tokamak with long pulse duration capabilities currently equipped with an ITER-grade actively cooled divertor, including shaped monoblocks with a 0.5 mm height toroidal bevel as foreseen for ITER, while AUG allows the exposure of dedicated tile-sized samples (with different geometries, gap sizes, slopes and materials) in ELMy H-mode discharges using its divertor manipulator DIM-II system. The first part of the paper reports on the 4 year long operation of the ITER-grade PFCs in WEST since the commissioning of the divertor in 2022. The second part of the paper presents dedicated experiments performed in AUG and WEST in order to study W failure modes, W melting across toroidal gaps (during sustained or transient melting) and the impact of the runaway electrons on W material. The results reported here provide new information on the W material response (e.g. heating, cracking or melting) of direct relevance to ITER.