Plasma decay in N₂, CO₂and H₂O excited by high-voltage nanosecond discharge

Abstract

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.

Nonequilibrium Plasma Aerodynamics

“…Therefore, the lifetime of the plasma was overestimated in [Schneider et al, 2004] approximately by an order of magnitude. This follows also from direct measurements of the effective recombination rates in room temperature N 2 , CO 2 and H 2 O under conditions close to those for MHD-controlled inlets were performed in papers ( [Zhukov et al, 2006;Aleksandrov et al, 2007aAleksandrov et al, ,2007bAleksandrov et al, ,2008Aleksandrov et al, ,2009), and in air in paper [Aleksandrov et al, 2011]. Discharge was initiated in a quartz tube of inner diameter 47 mm and outer diameter 50 mm, the metallic electrodes being at the ends of the tube.…”

“…In this case, O 4 + ions have no time to form from O 2 + ions in the discharge phase and in the discharge afterglow. However, measurements [Aleksandrov et al, 2011] showed that in this case the predominance of O 2 + ions does not necessarily lead to increasing the lifetime of the air plasma. Let us consider this point in more detail.…”

“…Figure 26 shows typical electron density histories measured, respectively, in N 2 , O 2 , CO 2 and H 2 O at a discharge repetitive frequency of 2 Hz. The positive ion composition can be dominated by simple O 2 + ions in a high-voltage nanosecond discharge in room-temperature air (see calculations in [Aleksandrov et al, 2011]). In this case, O 4 + ions have no time to form from O 2 + ions in the discharge phase and in the discharge afterglow.…”

“…[Aleksandrov et al, 2007a[Aleksandrov et al, , 2007b. Figure 28 compares the evolution in time of the electron density measured in [Aleksandrov et al, 2011] during the discharge afterglow and that of the electron density calculated using the generally accepted rate constants for electron loss [Kossyi et al, 1992]. The difference between the measurements and calculations reached a f a c t o r o f t h r e e , m u c h h i g h e r t h a n t h e experimental error of the electron density measurements that was around 20-30%.…”

“…28. The evolution in time of the electron density in the nanosecond discharge afterglow in air for 8 Torr [Aleksandrov et al, 2011]. Curve 1 corresponds to measurements.…”