Electromagnetic interference signal frequencies caused by discharges within spacecraft

The electron caused electromagnetic pulse (ECEMP) internal response of a cluttered cavity with the geometry characteristics of a spacecraft (DSCS II) is computed and analyzed for a typical current distribution caused by dielectric discharge. A pulsed discharge across a narrow gap in the cavity interior is considered, and the frequency of the response is found to be much lower than expected from the lowest mode of an uncluttered cavity. The effect can be thought of as due to the 'loading' of a basic coaxial cavity by the impedances corresponding to the cluttering structures. The phenomenon is considered analytically and numerically for the simple case of capacitive loading due only to a narrow gap. It is shown that for special cases, the problem of frequency response can be reduced to the matching of the impedance characterizing the coaxial cylinder with the impedance of the narrow gap.