Self-Consistent Atmospheric EMP Coupling in Three Dimensions

This article describes a three-dimensional, finite-difference solution and program for self-consistent treatment of Maxwell's equations in air in the presence of an ionizing radiation pulse. The solution is based on polar coordinates, and gives the surface current density on a conducting body. Ionizing radiation generates primary Compton electrons, which in turn create secondary electrons and electromagnetic fields. Our solution yields these fields, and then self-consistently tracks the Compton-electron trajectories in the fields. It also determines the air conductivity due to the secondary-electron and air-ion densities, and correspondingly modifies the electromagnetic-field propagation. Finally, it keeps account of the air-ion and secondary-electron density changes due to generation by primary electrons, avalanche, and recombination. Numerical results are presented for the current on a vertical conducting post 2m high and 15cm in diameter when exposed to a 1 MeV γ pulse of 2×1012 rads/sec peak amplitude and 40 nsec FWHM. These results are presented for the ancle of γ incidence 10° and 45° from horizontal. For comparison, we show the way omission of self-consistency and/or γ-shadowing modifies the current.