Plasma decay in N₂, CO₂ and H₂O excited by high-voltage nanosecond discharge

Plasma decay after a high-voltage nanosecond discharge was studied experimentally and numerically in room temperature N₂, CO₂ and H₂O for pressures between 1 and 10 Torr. The time-resolved electron density was measured by a microwave interferometer for initial electron densities in the range 8 × 10¹¹-3 × 10¹² cm^-3 and the effective electron-ion recombination coefficient was determined. It was shown that this coefficient varies in time and depends on pressure. A numerical simulation was carried out to describe the temporal evolution of the densities of charged particles under the conditions considered. A good agreement was obtained between the calculated and the measured electron density histories. It was shown that the loss of electrons is governed by dissociative recombination with complex ions, their density being dependent on pressure. In N₂ at low pressures, a hindered electron thermalization in collisions with molecules led to a delay in the plasma decay. This effect was observed both experimentally and theoretically.