The luminous events produced by a drifting relativistic electron beam (REB) (1–2 MeV, 100 kA, 40 nsec) have been photographed with an image converter of 5-nsec gate time. Coupled with a transmission spectrograph, time-gated snapshots (1 μsec) of the spectra have been recorded. For air pressure between 0.1 and 0.3 Torr, the beam is self-focused and it yields a spark spectrum containing mainly N+, with some O+ and N++ lines. In 0.8–1 Torr of air, the beam is unfocused and it yields the N2 (B←C) but not the (A←B) bands. In the presence of a target, the unfocused beam may again produce an air breakdown. A slitless spectrum then yields a two-dimensional image of the event, which may be related to the spatial distribution of the beam. The results are discussed in connection with REB and ion acceleration research. In addition, Lichtenberg-type discharge tracks in a Plexiglas disk irradiated by 2-MeV beams are photographed and compared with the fluorescence lifetime of the N2 (B←C) bands.

New results on the plasmas produced by an e-beam in a vacuum diode are presented. In the near-uv range, we measure the plasma expansion speeds by the Doppler-shift and by the time-of-flight methods. The maximum observed speed of 2.4×107 cm/sec for the C+3 ions leads us to estimate the electric field which is probably in the range of 1–6 kV/cm and may exist for tens of nsec. Some aspects of the spectral characteristics, the collective field effect, and the partition of the discharge energy are discussed in connection with recent literature.

A self-focused electron beam produces a string of hot spots along its path in 0.35 Torr of air. In this communication we report some interesting snap shots on the luminous gas bubbles expanding from the pinched hot spots. The radial speed of expansion is measured to be ∼9 mm/μsec, which corresponds to ∼6 eV of kinetic energy per N+ ion.

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