SYMPOSIA PAPER Published: 01 January 1983
STP37288S

Increased Breakdown Thresholds in Air by Admixing an Electronegative Gas

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The intrinsic breakdown by large area laser beams of gases containing the attaching species SF6 mixed with clean dry Air has been analyzed in detail. The results show that SF6 is equally effective in inhibiting avalanche breakdown of these gases for near infrared pulses longer than 100 nanoseconds as for DC fields. The breakdown intensities were obtained for various pulse durations at 10.6 μm by numerically solving the Boltzmann equation for the energy distribution n(ε) of electrons in the generated plasma. Published electron collision cross sections considered the best available for our application were used. The calculated breakdown intensity for very long pulses of constant intensity in air at 1 atm and 300K is I* = 2.7 × 109 w/cm2, which agrees within experimental uncertainty with the measured value. At any given intensity, the power absorbed by the plasma and the power losses in the various electron collision processes (elastic, inelastic excitation of vibrational and electronic levels, ionization, and attachment) are evaluated in our calculations. Discrete photon effects in power absorption and photoelectric processes are expected to be small for wavelengths larger than 1 μm, so the frequency scaling (I*/ω2) of classical field theory should hold for our results over the near infrared region.

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Volkin, HC
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Developed by Committee: F01
Pages: 617–628
DOI: 10.1520/STP37288S
ISBN-EB: 978-0-8031-4865-9
ISBN-13: 978-0-8031-0708-3