ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Measurements and analyses have been made of electron impact ionization and of current growth in pulsed, low-current, prebreakdown discharges in parallel-plane geometry in N2 at very high electric field to gas density ratios E/n and low products of the gas density n and electrode separation d. The E/n range and nd ranges were 1〈E/n〈52 kTd, where 1 Td=10−21 V m2 , and 6×1018 〈nd〈3×1020 m−2 (or 0.02〈pd〈1 Torr cm, where p is pressure) and were below breakdown values. Measurements were made of the transported charge on the time scales of electron transit, ion transit, and metastable decay. Measurements were also made of the growth of steady-state discharge currents as a function of discharge voltage. The contributions of avalanches resulting from ion- and metastable-induced secondary electrons were determined from the ratio of electron-excited N+2 391.4-nm emission integrated over all avalanches to the integrated emission during the laser-initiated electron pulse. Calculations based on ionization by electrons only show good agreement with the measured charge transported during the electron avalanche and with the current multiplication. Analysis of 391.4-nm emission data and of charge transported at E/n≥10 kTd and voltages near breakdown using the assumption of electron impact ionization leads to large apparent secondary electron yields at the cathode which increase significantly with nd. At E/n≥10 kTd, and for the voltages of our experiments, fast N2 produced in charge transfer collisions of N+2 with N2 appears to provide most of the secondary electrons. The apparently small contribution of ionization of N2 by N2, N+2 , N, and N+ is consistent with our assumption that each of these ionization cross sections is equal to that for N2-N2 collisions and so are much smaller than for Ar+ -Ar or Ar-Ar collisions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.342651
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