Study of self-focusing electron beams by the spectroscopic method

Propagation and focusing of intense relativistic electron beams (1-2 MeV, 100 kA, 40 nsec) in lowpressure air have been studied by fast photography and emission spectroscopy. For pressure in the range of 0.1 to 0.3 torr, the beam is self-focused and it yields a spark spectrum containing mainly N+ lines. Above about 0.8 torr, the beam is unfocused and it yields the 2nd positive band of N2. In this paper, the authors present some preliminary results obtained in the intermediate pressures when the beam changes from an unfocused condition to a focused condition. Using a concave grating (600L/mm) mounted on a 1-meter Rowland circle, the authors have photographed the spectrum in a spatially resolved arrangement