Studies to reduce material erosion in electrothermal launchers

Plasma erosion processes on insulators and conductors, using the SIRENS electrothermal launcher, have verified the vapor shield concept. The energy transmission factor through the vapor shield was found to vary from 20% to 5% as the heat flux increases. Metals have strong axial erosion dependence, with an average erosion depth of 15-45 μm/kJ for aluminium and 5-10 μm/kJ for pure copper. Insulators have uniform ablation along the axial direction, with an average ablation depth of 10-14 μm/kJ for Lexan. Aluminium has a higher erosion rate with an increase of energy input, while Lexan and pure copper have approximately equal erosion rates which are considerably less than that of aluminium. High-density graphite does not ablate at lower energies, and ablates only slightly at energies above 3 kJ (1-2 μm/kJ), while molded dense electrographite ablates at a higher rate (1-3 μm/kJ). Both types of graphite have considerably less ablation than other materials. Lexan and graphites showed greater evidence of the vapor shield effect than aluminium and copper, although there is tendency towards less erosion at higher values of heat fluxes. Multiple exposure of material surfaces demonstrated that insulators have better performance than metallic surfaces. The initial indications for the effect of the magnetic field applied parallel to the material surface revealed a threshold for the onset of the magnetic vapor shielding effect (above 5 T for Lexan)