Parametric studies of high-heat-flux-induced erosion of surfaces in an electrothermal accelerator

Ablation and melting of surfaces in devices such as electromagnetic launchers and electrothermal accelerators is of fundamental concern. The plasmas in these devices can exposes surfaces to intense heat fluxes. In order to increase lifetime and maximize device efficiency, erosion of critical components (e.g., rails, insulators, barrels) must be kept to a minimum. Numerous materials have been tested as to whether they survive realistic conditions. However, the fundamental mechanisms of energy transport through the plasma region immediately adjacent to the surface have largely been unexplored. This plasma boundary layer region is referred to as the vapor shield because they vapor absorbs the incoming energy (as internal energy) and prevents it from reaching the surface. This region is characterized by large temperature and density gradients and is dominated by the source of ablated surface material and the absorption of incident energy. It is predicted that the addition of a strong magnetic field parallel to the surface will affect the energy transport in the vapor shield by reducing crossfield thermal conduction and possibly increasing the radiation energy density. The authors report on experimental efforts to verify the existence of the vapor shield and to measure the effectiveness of the shield in reducing the surface erosion