Approaches to Mitigate Disruption of Telemetry During Directed Energy Testing

Abstract

Testing of directed-energy weapon systems requires continuous radio-wave telemetry in order to characterize in situ the effect of irradiation on a target. The telemetry in these cases might be disrupted due to plasma formation causing communication blackout. In this paper several mitigation approaches, namely electrostatic and electromagnetic, are considered. The electrostatic mitigation approach takes into account that an electron depleted sheath is formed around the negatively biased electrode. This creates a 'hole' in the electron density distribution allowing radio communication through the plasma. The electromagnetic approach is based on formation of the ExB layer in the plasma, consequent plasma acceleration, and resulting decrease in the plasma density. In order to assess these mitigation approaches, one needs to characterize the plasma which is created as a result of laser irradiation on different target materials and under various laser beam power levels. We developed a model of the plasma formation which is based on a kinetic description of the Knudsen layer and a hydrodynamic description of the collision-dominated plasma region which is coupled with analyses of the heat transfer in the target material. The overall model describes the absorption of the laser energy by the target and the resulting temperature rise in the surface. This temperature rise then induces ablation of the target material. Laser energy absorption by the plasma plume created above the surface is also considered. Analysis of the ablation rate of various targets subject to directed energy impact was performed. We considered a typical multilayer structure consisting of black paint, titanium, and aluminum layers. For instance, it was found that the aluminum layer has the highest ablation rate, while the black pain layer has the smallest rate for a given surface temperature.