Formative Time for Breakdown in Strong Crossed Fields
Abstract
The formative time of electric breakdown in low-pressure (0.2-2.0 Torr) hydrogen across a strong magnetic field (10<ωbτ<350; maximum B of 18 kG) has been measured in a coaxial cylindrical geometry. Attention was centered on the region of breakdown that occurs with a formative time less than the time required for an electron to drift across the electrode gap in the applied fields. This crossing time was inferred by extrapolations of previous measurements by Bernstein. These formative time measurements are compared with a simplified theory that assumes a constant number of e-folding times until breakdown and neglects electron losses as well as secondary production at the cathode. This model predicts that the formative time is inversely porportional to the gas pressure and otherwise a function of only the ratio E/B and not of either field separately. The predicted pressure dependence is confirmed, but some deviations from the predicted functional dependence on E/B are found. These deviations are attributed to electron losses along the magnetic field. A prediction of the magnitude of the formative time based on this simplified theory must necessarily involve extrapolation of certain previously obtained results. Such a prediction is found to be in reasonable agreement with the experimental values.
- Publication:
-
Journal of Applied Physics
- Pub Date:
- April 1968
- DOI:
- 10.1063/1.1656557
- Bibcode:
- 1968JAP....39.2343S