PPPL-3662 is available in pdf format.

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

Authors: C.H. Skinner, C.A. Gentile, and A. Hassanein

Date of PPPL Report: January 2002

Presented at: the IEEE/NPSS Symposium on Fusion Engineering in Atlantic City, NJ, January 21-25, 2002.

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/mm2 and scanned at high speed over the surface of carbon tiles. These tiles were previously used in the TFTR [Tokamak Fusion Test Reactor] 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 degrees C while for the same conditions, the manufactured surface increased to only 1,080 degrees 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 approximately 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.