Geomagnetic EMP: Field Calculations

This report presents improvements on a theory describing the electromagnetic fields generated by prompt gamma radiation from a low altitude (up to 25 km) nuclear explosion, the so called electromagnetic pulse, EMP. It examines in some detail various parameters from the point of view of making a computer program implementation. The contribution to the EMP from the air-ground(sea surface) discontinuity is not taken into account. Example calculations of current density, secondary electron conductivity and electric field are given for some illustrative cases. It is demonstrated that the main contribution to the EMP due to synchrotron radiation comes from a comparatively small region around the explosion thereby giving some credit to the use of constant approximations to non-constant parameters. Comparison is made with results from the original formulation showing that the theoretical improvements do not have a big numerical impact on the magnitude of the electric field except relatively close to the explosion. By comparison with openly published data it is shown that the C++ program used for calculation at its current state gives results that generally are considerably smaller except for altitudes 10 km and above and not very far away from the explosion. Finally an outlook is given listing outstanding issues to be addressed in future work, e.g.(not in order of priority), investigation of parameters related to the current and conductivity calculation, reformulation of the C++ code describing the magnetic field dependence, self-consistent calculations of magnetic field and current density, investigation of absorption processes for the secondary electrons and inuence of, e.g., difierent types of weapon.