Experimental measurements of melting and vaporization due to simulated plasma disruptions

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Abstract
The first wall and limiter surfaces of magnetic confinement fusion devices will be subjected to intense pulsed thermal loads due to plasma disruptions which can result in vaporization and melting limiting the lifetime of these components. This paper presents experimental data on the vaporization and melting of AXF-5Q graphite, Type 316 stainless steel, OFHC copper and tantalum due to thermal loads varying up to 2400 J/cm2 applied for times between 1 and 50 ms. The surface thermal loads were simulated with a 120-keV electron beam in the electron beam surface heating (ESURF) facility. The analysis procedure consisted of determining vaporization losses through weight-loss measurements and evaluation of the melt zone thickness through a metallographic sectioning procedure. Comparisons with some of the more recent theoretical predictions are made. The data trends (i.e., increasing melt and vaporization with energy density, existence of threshold energy densities, and melt thickness limits at high energy density due to increased vaporization) are generally found to agree with the analytical predictions. However, the magnitude of the melt zone thicknesses and vaporization losses show differences significant enough to warrant investigation of both modeling assumptions and the experimental techniques and conditions.

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