Performance of different tungsten grades under transient thermal loads

TLDR

Plasma‑facing components in future fusion devices will experience intense transient thermal loads from edge localized modes and disruptions, and to avoid irreversible damage the local energy deposition must stay below the damage threshold, which for monolithic tungsten exceeds ≈0.3 GW m⁻² in 1 ms bursts, while ITER‑like thin tungsten coatings on carbon–fibre composites have thresholds roughly half that value. High‑cycle ELM‑simulation tests on actively cooled bulk tungsten targets show no cracks up to 0.2 GW m⁻² at 0.8 ms and 10⁴ cycles, but cracks appear at 0.27 GW m⁻² with 0.5 ms pulses after 10⁶ cycles.

Abstract

Plasma facing components in future thermonuclear fusion devices will be subjected to intense transient thermal loads due to type I edge localized modes (ELMs), plasma disruptions, etc. To exclude irreversible damage to the divertor targets, local energy deposition must remain below the damage threshold for the selected wall materials. For monolithic tungsten (pure tungsten and tungsten alloys) power densities above ≈0.3 GW m −2 with 1 ms duration result in the formation of a dense crack network. Thin tungsten coatings for the so-called ITER-like wall in JET, which have been deposited on a two-directional carbon–fibre composite (CFC) material, are even less resistant to thermal shock damage; here the threshold values are by a factor of 2 lower. First ELM-simulation experiments with high cycle numbers up to 10 4 cycles on actively cooled bulk tungsten targets do not reveal any cracks for absorbed power densities up to 0.2 GW m −2 and ELM-durations in the sub-millisecond range (0.8 ms); at somewhat higher power densities (0.27 GW m −2 , Δ t = 0.5 ms) cracks have been detected for 10 6 cycles.