Attenuation and Refraction of an Electromagnetic Wave in an Electron Beam Generated Plasma

摘要

Artificially generated plasmas may be employed to alter the propagation characteristics of electromagnetic waves. The purpose of this report is to study the propagation of electromagnetic waves in an electron beam generated plasma. To understand the physics related to this concept requires the development of computational tools dealing with a plasma created by an electron beam, an assessment of the temporal and spatial evolution of the plasma, and a characterization of the refraction and attenuation of electromagnetic (EM) waves in a collisional plasma. Three computer programs were developed to characterize the effectiveness of an electron beam generated plasma in refracting and attenuating an EM wave. The spatial extent and density distribution of a plasma generated by a relativistic electron beam were determined using an axisymmetric Monte Carlo model. This plasma density distribution was used as a source term in the second code, a temporal solution of the plasma evolution based on a time dependent analysis of the plasma rate equations. The third code developed, evaluates the attenuation and refraction of an EM wave in the resulting plasma by using a ray tracing method based on the eikonal approach of Sommerfeld. The theoretical foundation and validation procedures are presented for each program. A limited exploration of the dependence of the plasma distribution on neutral densities and the electron beam energies was performed. For neutral densities corresponding to 5 km altitude, the plasma longitudinal extent ranged from 52 to 868 cm and the radial extent ranged from 18 to 292 cm for initial electron energies between 100 keV and 1 MeV respectively. Plasma chemistry plays a critical role in determining the electron plasma density and dictates the beam format required to achieve a desired level of EM wave attenuation.