Large-Area Electron-Beam Experiments on Space-Charge Neutralization in a Cavity

This paper presents an experimental and analytical description of IEMP produced with electron beams. Time-dependent measurements are reported of the radial distribution of the current transmitted across a 12-inch-diameter cylindrical cavity, as a function of air pressure within the cavity, for two types of electron pulses - a short pulse of 4 kA peak, 30-nsec FWHM, and a long pulse of 10 kA peak, 100-nsec FWHM. Measurements of the injected beam parameters are also reported, including a determination of the spectrum of the emitted electrons as a function of time, using a simple magnetic spectrometer. DYNACYL calculations of transmitted current as a function of air pressure for the short-electron-pulse case are summarized. The DYNACYL calculations give a qualitative description of the transmitted current time history, in most cases agreeing within a factor of 2 with the experimental data. Discrepancies are thought, in some instances, to be due to inaccurate specification of the injected beam parameters, as well as to the simplifications employed in the computer code.