Air Effects on the External SGEMP Response of a Cylinder

Effects of air on the external SGEMP response of a cylinder in the x-ray deposition region (50 to 100 km) are examined. The gross external response of a missile is modeled using an object exposed to a variety of x-ray and air environments. Responses are computed using a macroparticle treatment for both primary and secondary electrons which move self-consistently in the electromagnetic fields. Surface currents of approximately 10,000 A/m are coupled to the cylinder for air pressures corresponding to 50 to 60 km. Preionization of the air results in coupled currents up to 5,000 A/m at higher altitudes. These currents are both significantly higher than any postulated to date. It is also significant that they can occur with large electric fields such as result in the vacuum case.