High Heat Flux Interactions and Tritium Removal from Plasma Facing Components by a Scanning Laser

Abstract

A new technique for studying high heat flux interactions with plasma facing components is presented. The beam from a continuous wave 300 W neodymium laser was focussed to 80 W/mm 2 and scanned at high speed over the surface of carbon tiles. These tiles were previously used in the TFTR inner limiter and have a surface layer of amorphous hydrogenated carbon that was codeposited during plasma operations. Laser scanning released up to 84% of the codeposited tritium. The temperature rise of the codeposit on the tiles was significantly higher than that of the manufactured material. In one experiment, the codeposit surface temperature rose to 1,770°C while for the same conditions, the manufactured surface increased to only 1,080 °C. The peak temperature did not follow the usual square-root dependence on heat pulse duration. Durations of order 100 ms resulted in brittle destruction and material loss from the surface, while a duration of ≈10 ms showed minimal change. A digital microscope imaged the codeposit before, during and after the interaction with the laser and revealed hot spots on a 100-micron scale. These results will be compared to analytic modeling and are relevant to the response of plasma facing components to disruptions and vertical displacement events (VDEs) in next-step magnetic fusion devices.

Review of D-T Experiments Relevant to Burning Plasma Issues

“…The tiles were scanned with a laser to heat the surface and release the tritium from the codeposited layers [94][95]. Initial results look promising and the possibility of using this technique on future JET experiments is being discussed.…”