Diagnostics Development for E-Beam Excited Air Channels. Conductivity Measurements in Air Afterglows
Semiannual technical rept. no. 2
SRI INTERNATIONAL MENLO PARK CA
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Nonintrusive techniques for measuring conductivity decay in the afterglow air channel of a relativistic electron beam are reviewed, and the microwave cavity perturbation technique is found to offer adequate sensitivity. A right cylindrical cavity resonating in the TM 010 mode at 1.5 GHz was fabricated, and a series of preliminary measurements in air was performed. The afterglow conductivity of laboratory air at 1 amagat is apparently dominated by ions. The conductivities of synthetic air at 10 torr at 250 to 1500 microseconds after the pulse are consistent with electron densities of 10 to the 8th power to 5,000,000cc and electron temperatures of approximately 0.15 eV. Surveys of conductivity histories at 5 pressures between 10 and 760 Torr are also reported. After the experimental set-up has been refined, conductivity studies in room temperature air will be repeated. Future work will include measurements on the ETA facility, measurements of shock-heated air, and measurements to investigate the field-induced detachment of negative ions in the afterglow.
- Particle Accelerators
- Plasma Physics and Magnetohydrodynamics