Topanga Simulations of Starfish Prime: Diamagnetic Cavity Evolution and Flux Tube Motion

We present kinetic simulations of the Starfish Prime high altitude nuclear explosion (HANE) using the code Topanga with an emphasis on diamagnetic cavity and flux tube evolution in the Earth's magnetosphere following the burst. The diamagnetic cavity forms in approximately a second, while the associated flux tube takes approximately thirty seconds to decay. Full cavity closure in the simulations takes approximately forty seconds.

During this timeframe, the flux tube undergoes coherent motion rising upward thousands of kilometers. We elucidate the mechanism of flux tube rise, which bears a striking resemblance to blob motion in the tokamak edge layer. Ionized debris traveling along curved magnetic field lines experiences a centrifugal force that is directed radially outward. This results in charge separation across the flux tube and an electric field that is directed predominantly eastward. This eastward directed electric field generates a radially outward ExB drift in the Earth's magnetic field, which is responsible for coherent flux tube rise.

Our results have applications to understanding the perturbed space environment following a HANE. In particular, flux tube rise modifies the injection of electrons into artificial radiation belts following a HANE, which pose a hazard to satellites.