EMPPIC: A PIC Code for Nuclear Electromagnetic Pulse.

The nuclear electromagnetic pulse (NEMP) is a pulsed electromagnetic wave generated by the prompt gamma emitted from a nuclear explosion. In the 1970s, Longley and Longmire proposed a simulation method for the NEMP, which has been widely used in the NEMP simulation such as the widely used code CHAP. Constrained by the computational capabilities of the time, the CHAP program relied on numerous assumptions, which have been scrutinized in recent years. In addition to the CHAP method, in 2016, Friedman et al. proposed the idea of constructing a NEMP program based on the Particle‐in‐Cell (PIC) method. The PIC method not only accurately simulates the dynamics of electrons but also self‐consistently simulates the influence of pulsed electromagnetic fields on electrons, and requires fewer assumptions. Unfortunately, due to the excessively computational consuming of the PIC method, Friedman et al. couldn't simulate the full‐scale NEMP spanning tens of kilometers. In this paper, we present the first full‐scale simulation program for the NEMP based on the PIC‐fluid coupling method. By utilizing the moving window method, double‐grid methods and linked list storage techniques, we significantly reduce the computational consuming. Additionally, a mixed scattering collision method is used to efficiently simulate elastic collisions between Compton electrons and atmospheric molecules. Detailed discussions of the relevant simulation results are also provided. Plain Language Summary: Recently, we developed a simulation program for NEMP (Nuclear Electromagnetic Pulse) using the Particle‐in‐Cell (PIC) method to model Compton electron motion and the swarm method for conduction electron motion. This program, named EMPPIC (Electromagnetic Pulse via Particle in Cell), is the first full‐scale NEMP simulation tool based on the PIC method. To overcome computational challenges faced by previous researchers using the PIC method, the program incorporates a moving window approach and a linked‐list storage technique. Additionally, to address numerical dispersion issues encountered when solving Maxwell's equations with the FDTD method, we employ a dual‐grid system: a coarser grid for simulating electron motion and a finer grid for solving the electromagnetic field. Information exchange between the current and electromagnetic fields is achieved through interpolation between these two grids, effectively mitigating dispersion effects while keeping the computational demands manageable. Key Points: This program named EMPPIC is the first full‐scale simulation program for the NEMP based on the PIC methodThe profile of average energy of conduction electrons lags behind the migration speed, indicating the presence of a thermalization processIf only considering small‐angle scattering, the amplitude would be overestimated by approximately 13%, consistent with previous research [ABSTRACT FROM AUTHOR]