Formation of ionization channel in high-pressure gas using pulsed relativistic electron beam

The formation of an ionization channel in a high-pressure gas using a 109-W 50-nsec pulse of 500-keV electrons has been investigated. A 3-kA electron beam was injected into air, hydrogen, and helium at pressures ranging from 0.2 to 600 Torr in the presence of applied magnetic guide fields ranging up to 6 kG. It was found that the resultant beam-spreading data can be explained on the basis of elastic scattering, and that magnetic fields of a few kG can be expected to effectively control beam spread in hydrogen (and helium) up to 2 atm. Rapid loss of the plasma after the passage of the beam was observed and has been interpreted to be the rapid recombination of a very cold plasma left behind by the beam. This mechanism appears to be an attractive alternative to laser preionization of a long high-pressure Z pinch experiment.