Nonlinear self-consistent calculations of radiation induced cylinder skin currents

The particle method of numerical plasma simulation is applied to the calculation of surface currents on a metallic cylinder in air, exposed to an axially directed planar wavefront of gamma radiation. Assuming a collision-dominated plasma, the Compton electron trajectories, rate equations for the production of secondary electrons and the Maxwell equations are advanced self-consistently for each time step at all mesh cells in the finite difference solution. Numerical results presented include comparisons of self-consistent skin currents with results obtained by prescribing (no field reaction) the Compton current density and ionization rate proportional to the gamma flux. With a sin² pulse of 40 ns duration and a relative air density of 1, the self-consistent surface current magnitudes lie considerably below prescribed source results for peak gamma dose rates ≥ 10¹¹ Rad/sec. At 10⁹ Rad/sec, the skin currents from the particle calculations are nearly identical with currents resulting from a prescribed source obtained from the electron dynamics in the absence of the Lorentz force.