Numerical Simulation of X-Ray-Induced Coaxial Cables SGEMP Using Monte Carlo and Maxwell-FDTD Methods with Nonuniform Charge Distributions

Abstract: System-generated electromagnetic pulse (SGEMP) induced in coaxial cables by X-ray irradiation can interfere with diagnostic signals in inertial confinement fusion and pulsed radiation experiments. In this paper, the nonuniform net charge distribution obtained from coupled photon-electron transport in MCNP5 is introduced into a twodimensional axisymmetric Maxwell finite-difference time-domain (FDTD) model to evaluate the cable SGEMP response. To assess the consistency of the numerical predictions, the calculated current responses of the coaxial cable under X-ray irradiation are compared with those obtained using the equivalent transmission-line method reported in a previous study. The current responses under uniform and nonuniform charge distribution conditions are compared, and the results show that the assumption of uniform charge deposition overestimates the peak response by more than an order of magnitude. A transverse electromagnetic mode analysis explains the underlying mechanism: the spatial weighting of dielectric charge and its cancellation with conductor charge jointly govern this discrepancy. This paper further examines the effects of irradiation conditions, cable length and materials, and termination conditions on the SGEMP current response of the cable. This study can provide theoretical guidance for the radiation hardening of cables.