Electron Density of Relativistic Electron Beam Produced Plasmas

A multiple-pass Mach-Zehnder laser-illuminated interferometer has been constructed and used to measure the electron density profile of plasmas produced by a self-confined propagating electron beam. Spatial and time resolved data were taken perpendicular to the electron beam axis at two longitudinal positions. Densities of 1016 cm−3 have been seen in air between 0.15 and 0.3 Torr as early as 150 nsec after the electron beam entrance. Peak densities of 1017 cm−3 were typically reached at around 2 μsec. Plasma compression was observed under some conditions.