Deionisation of the afterglow plasma due to accelerated ambipolar diffusion

Abstract

The accelerated ambipolar particle diffusion is simulated in the afterglow of discharges in He — Cu and Ne —Cu mixtures. The calculations showed that a heating field E ≈ 0.3 — 1.3 V cm-1 imposed on the afterglow discharge at a buffer gas pressure of 8 — 10 Torr and a tube diameter of 4 — 10 mm reduced the electron density by a factor of 102 — 104 for ~100 μs. The effect was shown to be most pronounced in helium. According to the calculations, the application of accelerated ambipolar diffusion during the interpulse period will increase the pulse repetition rate of copper vapour lasers with low-diameter tubes (4 — 6 mm) and low buffer-gas pressures (6 — 8 Torr) by 20% — 50%. The production of excessive prepulse density of the metastable states of copper can be prevented by interrupting the plasma heating 3 — 6 μs before the onset of the next excitation pulse.