Analysis of processes responsible for the memory effect in air at low pressures

Abstract

The memory effect in air at 0.7 and 6.6 mbar pressures, due to post-discharge survival of some species that affect subsequent breakdowns, was analysed using memory curves. In order to complete the analysis of the processes, memory curves for nitrogen have also been monitored, because air is 78% nitrogen. In an early afterglow, the memory effect in air, as well as in pure nitrogen, is a consequence of the same processes, i.e. the presence of N + 2 and N + 4 ions, formed by the collision between nitrogen metastable molecules from the previous discharge. The concentrations of nitrogen ions in an air-filled tube are lower than the concentration in a nitrogen-filled tube for a given afterglow period because of their recombination with O, O 2 and NO particles which are also present in the early afterglow in air. De-excitation of N 2 (A) and N 2 (a ) metastable molecules due to their collision with O 2 , O and O − particles also contributes to the reduction in the concentration of N + 2 and N + 4 ions. In the late afterglow in air and pure nitrogen, N( 4 S) atoms created during the previous discharge are responsible for the memory effect. In the early air afterglow N( 4 S) atoms can be formed by the collision of O + ions with N 2 (X) molecules. However, because of the relatively small concentration of these ions the most probable process is the recombination of N( 4 S) atoms with O 2 , O, NO and NO 2 particles. The net effect is that the concentration of N( 4 S) atoms in the late afterglow is less in air than in nitrogen. When the concentration of N( 4 S) atoms is sufficiently reduced, the breakdown is initiated by cosmic rays.

Free‐Electron Gas Spectrum Uniqueness in the Mixture of Noble Gases

“…It could be obviously seen that expression (9), which has been acquired in keeping with the ionization coefficient definition, corresponds with the experimental results in a wide range. Essentially, it is also perceptible that the equation (15) derived from the expression (12) yields far better results for the breakdown voltage of a noble gas mixture when compared to those supported by the equations (3) and (4), respectively. To be precise, the breakdown voltage values attained through ionization coefficients, provided by equations (3) and (4), tally the measured data only within the range the coefficients of which have been ascertained.…”

“…The same figure shows the calculated Paschen curves obtained by using equation (12) in which the first Townsend coefficient took values from the equations (3), (4) and (9), respectively. Curves in Figure 3 demonstrate the way in which the breakdown voltage of the gas mixture (1 − χ) Xe + χ Ar, provided through the equation (15), relies on the pd product with the percentage share χ as a parameter (10%, 30%, 50% and 70% of Argon in the mixture, respectively). Figure 4 displays the theoretically obtained Paschen curve for the mixture 0.3 Xe + 0.7 Ar with the pertinent experimental points.…”

“…In order to obtain curves in Figures 4 and 5 the two methods are used for fitting the curve. The first one used constants Z A and Z B taken from the Table 3., while the other one used the unique mixture constant Z(Z = Z A = Z B ) in the equation (15). Fig.…”

“…To begin with, γ in equation (12) represents the secondary ionization coefficient, or to be exact, the secondary electrons' number that is generated per one primary avalanche [14][15][16], and d the inter-electrode gap. Table 4.…”

Study of the synergistic effect in dielectric breakdown property of CO2–O2 mixtures

“…The U shape of Paschen curves has been well investigated, and different breakdown mechanisms, such as streamer, Townsend, anomalous Paschen and vacuum mechanisms, have been found to follow the relationship described by Paschen curves. 16,17 Generally, when the distance between electrodes is smaller than the mean free path of electrons, Paschen's law no longer holds, and the vacuum mechanism dominates. The present study focuses on the conditions of relatively large pd products where Paschen's law applies.…”