Recombination of electrons with water cluster ions in the afterglow of a high-voltage nanosecond discharge

Abstract

The results of the experimental and numerical study of high-voltage nanosecond discharge afterglow in H2O:N2 and H2O:O2 mixtures are presented for room temperature and at pressures from 2 to 5 Torr. Time-resolved electron density during the plasma decay was measured with a microwave interferometer for initial electron densities in the range between 1 × 1012 and 2 × 1012 cm−3. Calculations showed that the plasma decay was controlled by recombination of thermalized electrons with H3O+(H2O)n ions for n from 0 to 4. Agreement between calculated and measured electron density histories was obtained only when using the recombination coefficients measured in the pulsed plasma afterglow experiments. The electron densities calculated using the data from the storage ring experiments were consistently greater than the values measured in this work for all conditions. It was concluded that the measurements of recombination coefficients for H3O+(H2O)n ions in the pulsed plasma afterglow were more appropriate for simulating the properties of high-density plasmas with high fractions of H2O, O2 and N2, such as discharge plasmas in water vapor and in humid air instead of the measurements in the storage ring experiments.

Microsecond pulse gas–liquid discharges in atmospheric nitrogen and oxygen: Discharge mode, stability, and plasma characteristics

“…[ 22 ] In the afterglow, the three‐body recombination of ions assisted with H 2 O also consumes seed electrons to form molecular cluster ions H 3 O + (H 2 O) n . [ 23–25 ] These effects lead to the electric field distortion and the formation of streamer channels, which, in turn, enhances the discharge current. Consequently, the increase of the discharge current causes the discharge mode transition.…”

“…Gas heating in the nitrogen discharge is attributed to the electron‐impact dissociation of N 2 , the energy pooling of N 2 (A), and the quenching of N 2 (B) and N ( 2 P, 2 D), [ 23,26 ] which increases the liquid temperature and the fraction of water vapor in the working gas during the extended plasma process times. H 2 O molecules can absorb seed electrons and participate in the three‐body recombinaion of nitrogen molecular ion (N 2 + ) in the afterglow, [ 23,24 ] which affects the distribution of the electric field and favors the formation of streamer channels. Additionally, the rapid increase of liquid conductivity (Figure 9c), caused by the generation of aqueous reactive species in the nitrogen discharge, significantly affects the discharge instability after a period of 8 min.…”

Gasdynamic Flow Control by Ultrafast Local Heating in a Strongly Nonequilibrium Pulsed Plasma

“…In the case of H 3 O + (H 2 O) k hydrated ions (dominant positive ions in plasma decay in humid air), there are two types of experiments to measure the recombination rate coefficients, which give very (up to an order of magnitude) different results. These are direct measurements of the recombination rate coefficients from the decay rate of a plasma with hydrated ions at not too low (>1 Torr) pressures [106][107][108][109] and experiments at anomalously low (10 -11 Torr) pressures in ion accumulation rings [110][111][112], where the recombination cross sections are measured and the recombination coefficients are obtained by integrating the cross sections over the electron energy distribution. There is no doubt about the reliability of both types of measurements.…”

“…At present, there is only one explanation for this difference: it is assumed that the dissociative recombination of electrons with hydrated ions occurs by different mechanisms at very low and increased pressures [113]. Hence a practical conclusion follows from [113]: when simulating plasma decay in humid atmospheric-pressure air, it is necessary to use the recombination coefficients for hydrated ions obtained and verified in [106][107][108][109].…”

“…15 and 16 show the results of numerical zero-dimensional modeling of the evolution of the effective electron temperature and the charged particle densities in the afterglow of a discharge in dry and humid air at atmospheric pressure. The kinetic scheme of collisional processes describing plasma decay in this case is taken from [96,97,109]. In this case, the above-described specificities in collisional processes were taken into account.…”