Abstract

Optical observations of the air fluorescence show that the rate of energy deposition of a repetitively pulsed high-current-density relativistic electron beam increases with pulse number. The data suggest that the high electric fields of the second and later pulses accelerate the unrecombined electrons from previous pulses and create additional ionization and energy deposition by electron avalanche. As expected, this optical fluorescence enhancement is seen to increase as the air pressure is decreased, because the increased electron lifetime at lower pressures leaves a higher electron density when subsequent pulses arrive. Absolute calibration of electron beam current and optical intensities has permitted determination of the fluorescence efficiencies for each pulse as a function of atmospheric pressure. The fluorescence efficiencies for the first electron pulse reproduce previous observations of optical efficiency for ionizing radiation in air.

© 1989 Optical Society of America

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