Collisional particle-in-cell investigations of electromagnetic pulses in hypervelocity impact plasmas

A collisional, 2D discontinuous Galerkin particle-in-cell (DG-PIC) code is developed to analyze electromagnetic pulses (EMPs) generated from hypervelocity impact plasmas. The discontinuous Galerkin scheme is used to solve the 2D transverse electric Maxwell’s equations while the particle-in-cell scheme is used to model charged species dynamics. Two models for Coulomb collisions are tested: a small-angle “particle-moment” model and a general Langevin equation model. Both collisionless and collisional simulations are able to reliably reproduce EMP generation due to charge separation within the bulk and the resulting electrostatic oscillations that occur. Both collision models cause a decrease in the frequency of the EMPs that are formed; however, this decrease is not significant enough to explain the discrepancy between experiments and simulations in previous literature. Despite this, Coulomb collisions can be significant in the physics of the plasma behind EMP generation for hypervelocity impacts, particularly in increased heating within the plasma. Overall, although Coulomb collisions are highly influential in the temperature of the plasma, they are not important in the EMP generated and its threat to spacecraft.