Study of ionization and ion transfer rates in flowing N₂ DC discharges and post-discharges

Abstract

In this work, we studied the ionization and ion transfer rates in flowing nitrogen DC discharges and post-discharges. Two different experimental set-ups and conditions for the flowing nitrogen discharges were analyzed. The first experimental set-up includes a post-discharge tube where the pink afterglow phenomenon was detected. Two well-established discharge and post-discharge kinetic numerical models we had previously developed to study the nitrogen flowing DC discharges and post-discharges were employed to calculate the rates for our experimental conditions. We analyzed 18 ionization and nine ion transfer mechanisms for N + , N 2 + , N 3 + , and N 4+ ions in the discharges and post-discharges. We observed that the electron density of the discharges, which varies by one order of magnitude, plays a major role in the rates behavior for the two experimental set-ups. Moreover, we observed that the rates found in the pink afterglow phenomenon are relevant when compared to rates found in the discharges. The important role of molecular metastable Penning ionization and atoms and molecules associative ionization appear in the ionization rates of the discharges. It is also shown that ion transfer mechanisms play a crucial role in the ions densities distribution found in the discharges and post-discharges. This work brings an original comparative study of ionization and ion transfer rates for experimental flowing nitrogen DC positive columns and pink afterglow post-discharge. This is the first time that a detailed combined experimental and theoretical analysis on the ionization and ion transfer rates is carried out for nitrogen flowing DC positive columns and pink afterglow plasma.

Study of temporal dissociation and atomic excitation rates in a flowing N2 DC discharge and post-discharge

“…This fact evidences the effectiveness of dissociation mechanisms in the postdischarge. The same behavior has been found for the ionization rates of the pink afterglow as compared to ionization rates reached in the positive column [20]. The dissociation rates of the D10 reaction are very strong in the early post-discharge residence times, reflecting the high density of nitrogen-excited species early in the post-discharge.…”

“…The curves representing the dissociation rates for each specific reaction are defined in the figure legend. the discharge gas pressure results in an increase in the gas residence time [20]. However, they did not consider the occurrence of reaction D10 in their study.…”

“…We used the rotational transitions of the first positive system of nitrogen molecules [24] in the range of 760-780 nm [26]. The discharge gas residence time was calculated from a relationship between the inter-electrode distance and gas velocity [20]. The reduced electric field was calculated from the measured electric field at the Langmuir double probes and the Avogadro number of particles calculated for the measured gas temperature (T g ) and pressure.…”

“…In addition to the VME which accounts for electron-vibrational (e-V), vibrational-vibrational (V-V), and vibrational-translational (V-T) processes [3], the model accounts for 115 physicalchemical processes among neutral and excited molecular states, atoms, and ions [21]. This kinetic numerical model has been used to study the positive column atoms and molecules densities [21,29], and ionization and ion transfer processes [20,30].…”

“…The interesting feature of the pink afterglow is the fact that this nitrogen plasma is generated in the afterglow region, which is a zone where there is no direct influence of an external electric field. In our recent work [20], we studied the ionization and ion transfer mechanisms occurring in the positive column and pink afterglow plasma of nitrogen flowing DC discharges. We have observed that physical-chemical mechanisms such as the Penning ionization and associative ionization between electronically excited molecules and metastable atoms play a crucial role in the ionization of these plasmas, overcoming the electrons collisions ionization channels at certain discharges gas residence times in the positive column of discharges operating at high values of reduced electric field.…”