Radiation transport through a plasma boundary layer between armatures and material surfaces

The ablation of rail and insulator materials by plasma armatures limits the velocity and the component lifetime of electromagnetic launchers. The photon radiation from the armature is the dominant form of energy transfer causing the ablation. However, not all of the escaping radiation actually is transmitted to the ablating surface, and hence vapor shielding is said to occur in the plasma boundary layer. A one-dimensional time-dependent self-consistent hydrodynamics model with a multigroup flux-limited diffusion approximation for radiative transfer is used to estimate the energy transmission and the amount of ablated material. It has been found that the vapor shield is optically thin for photon energies where most of the incident source radiation is distributed, thus the simple diffusion model for radiative transfer would overestimate the radiation flux at the material surface. The multigroup flux limited diffusion model is used in order to overcome the problem of flux overestimation, and a formal solution of the steady-state radiative transfer equation has been derived in order to compare the results. The flux limiter of (c/2)U/sub g/, which represents a weak streaming behavior of photons and corresponds to the variable Eddington factor of 1/2, is found to give good agreement for surface heat fluxes.<
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