Diagnostics Development for E-Beam Excited Air Channels. Optical Studies of the PHERMEX Electron Beam
SRI INTERNATIONAL MENLO PARK CA
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Electron-induced fluorescence at selected uv wavelengths from the air channel excited by the PHERMEX electron beam facility at LANL was studied. Each beam pulse consisted of a sequence of 10 micropulses of 26 meV electrons of 200 A peak current lasting 3 ns. Individual micropulses were measured and analyzed. The 391.4-nm first negative emission from N2 was linear with beam current for all micropulses at all pressures. Thus, this emission band serves as an optical Faraday cup under these conditions. The 406.0-nm N2 second positive emission exhibited enhancements due to self-induced electric fields at pressures below 50 torr. The vibrational temperatures in the air channel rose during each pulse train to values ranging from about 750 to 1400 K. Very limited data indicates that the rotational temperature stays constant at approximately 300 K. Emission measurements made 20-m off the beam axis indicate that the induced intensity decays rapidly with propagation distance 30-50 in 6 meters. This suggests a much faster dissipation of beam energy than suggested deposition calculations. We observed no evidence for super radiant emission during tests at 580 torr.
- Nuclear Physics and Elementary Particle Physics