Plasma facing materials performance under ITER-relevant mitigated disruption photonic heat loads

Investigation of damages induced by ITER-relevant heat loads during massive gas injections on Beryllium

“…As soon as the combination of L abs and t was high enough (F HF ≥ 18 MW m −2 s 0.5 ) to cause a surface temperature above the melting threshold of Be, each MGI like heat pulse melted a Be layer with a depth of up to ∼120 μm due to the high penetration depth of the electrons in JUDITH 1. In contrast, a comparable heat load with F HF ∼ 22 MW m −2 s 0.5 exerted by a plasma onto the sample, would cause a melt layer thickness of 10-20 μm [3]. Thus, electron beam experiments with rather high acceleration voltages that enter the melting regime of Be tend to overestimate the melt layer thickness when compared to the more application related plasma loading experiments.…”

“…However, only up to ∼10 0 0 of the total number of discharges are expected to end with a high power mitigated disruption [3] . By using MGIs, the plasma cooling times range from 5-10 ms and the power densities L abs to the PFCs can be decreased to a moderate 90-260 MW m −2 .…”

“…One can derive the expected range of heat flux factors (F HF = L abs × t 0.5 , with t the pulse duration) from the plasma cooling times and the power densities, which yield F HF = 9-18 MW m −2 s 0.5 . This range represents the lowest loading condition (0.9 MJ m −2 , t = 10 ms) and the highest loading condition (1.3 MJ m −2 , t = 5 ms) that were applied in [3] .…”

“…To investigate the impact of MGI induced radiative loads to the PFCs, simulations [4] as well as experimental studies [3] have been carried out. Especially beryllium (Be) at the first wall (FW) and stainless steel at the port plugs could experience local melting by these loads due to toroidal and poloidal asymmetries [4] .…”

“…Especially beryllium (Be) at the first wall (FW) and stainless steel at the port plugs could experience local melting by these loads due to toroidal and poloidal asymmetries [4] . A detailed study with Be can be found in [3] , in which Be at a base temperature of 500 °C is subjected to intense photon pulses with F HF ∼ 22 MW m −2 s 0.5 and a pulse duration of 0.5 ms for up to 100 pulses. These parameters were chosen to investigate the melting behavior of Be under repetitive photonic heat pulses.…”