Topanga: A Modern Code for E3 Simulations

We are developing the Topanga code for simulating the generation and propagation of the E3 electromagnetic pulse. The E3 component has a long pulse, lasting tens to hundreds of seconds. It is caused by a nuclear detonation's temporary distortion of the Earth's magnetic field. E3 EMP has similarities to a geomagnetic storm~caused by a solar flare and can produce geomagnetically induced currents in long electrical conductors, damaging components such as power line transformers. Our code's attributes include the following: spherical geometry for simplified boundary conditions and computational efficiency; couples a hybrid plasma model (fluid electrons and neutrals, particle ions, Ohm's law, and reduced Maxwell's equations) to a finite-difference time-domain electromagnetic solver (FDTD-EM); uses the IGRF magnetic field model, neutral atmosphere profiles from the US Standard Atmosphere or the NRL MSISE model, ionosphere profiles from the International Reference Ionosphere model; has ion-neutral, electron-ion, electron-neutral collisions; uses a fluid algorithm for motion of the neutral atmosphere; and has limited atmospheric chemistry. An overview of the code and simulation examples with some comparison to experimental data will be presented