The effect of high-power transients on tungsten coatings used for radio frequency launcher applications

Radio frequency (RF) launchers often use a material coating on structural components, such as a high-conductivity material on the inside surfaces of the launcher or a high-temperature material for plasma-facing parts of the launcher. The coatings need to be robust enough to survive an arc or other transient event from the plasma (e.g., an edge localized mode) without causing a catastrophic failure of the coating. An RF-induced vacuum arc is being used to study the robustness of material coatings made by a variety of manufacturing techniques. A resonant 1/4-wavelength section of vacuum transmission line terminated with an open circuit electrode structure with a well-defined electric field (30-40 kV/m) produces repeatable arcing conditions. Arcing causes localized melting of the material and is often initiated on sharp microstructures on the surface. The transient time of the arc is on the order of microseconds, and the light emitted by the arc is being characterized by a spectrometer and/or a filterscope. The initial focus is on tungsten as a plasma-facing material, including sintered tungsten, additively manufactured tungsten, and tungsten coatings on steel produced via physical vapor deposition. Experimental details and results will be presented.