Memory effects in the afterglow: open questions on long-lived species and the role of surface processes

Abstract

The memory effect, the phenomenon that some active species survive very long afterglow periods and affect subsequent breakdown, was observed more than 40 years ago. The effects have been observed even over periods of several hours. Attempts to explain the memory effect in nitrogen were mostly based on hypothetical metastables and on the A3Σ state. However, such explanations had to neglect some quenching processes which are known to be very effective under the conditions of the experiments. The explanation based on atoms remaining from the previous discharge and recombining on the cathode to produce initial electrons was shown to be fully consistent with all the experimental data for nitrogen including a wide range of pressures and the addition of oxygen impurities. The memory effect was also shown to be sensitive to the work function of the cathode material. Thus, an attempt was made to use the memory effect as a diagnostic tool to establish the data on the dominant loss of nitrogen atoms from the discharge which is recombination on the walls of the tube. However, a possible role of higher vibrational levels has not been fully addressed, mainly due to the shortage of data. On the other hand, the memory effect which was observed for rare gases cannot be explained on the basis of the standard data unless the presence of molecular impurities is invoked. Another open issue would be the role of charges accumulated on the glass surfaces and whether those may be released to the gas phase. The aim of this paper is to summarize the achievements of the model based on atom recombination and to point out how the breakdown model associated with the memory effect may be completed and how it may be applied in practical discharges.

Conversion of an atomic to a molecular argon ion and low pressure argon relaxation

“…The transition from isothermal to free diffusion is described by the linear dependence D eff ∼ Λ /λ D . [23,35] 0 5.0T10 7 1.0T10 Besides the diffusion loss, the conversion plays an important role in the relaxation. Namely, the choice of conversion coefficient in the numerical model ((0.69 − 4.7) × 10 −31 cm 3 /s at the room temperature [11,28] ) plays an impor-tant role in modeling the relaxation.…”

“…[17,18] Elementary considerations show that metastable states are efficiently quenched by collisions between ground-state atoms and molecules of parent gases, as well as by collision with impurities and collision between themselves, their effective lifetimes in afterglow are reduced down to the order of milli-and microseconds and cannot explain the long-term memory. [19][20][21] Consequently, a new model was proposed to explain the memory effect in nitrogen based on the surface recombination of nitrogen atoms [21][22][23] and in hydrogen by surface recombination of hydrogen atoms. [23][24][25] The memory curve in argon was measured from very short relaxation times in afterglow up to the saturation region (determined by cosmic rays and natural radioactivity level) and was explained by the charged particle decay and after that, by surface recombination of nitrogen atoms present as impurities.…”

“…[19][20][21] Consequently, a new model was proposed to explain the memory effect in nitrogen based on the surface recombination of nitrogen atoms [21][22][23] and in hydrogen by surface recombination of hydrogen atoms. [23][24][25] The memory curve in argon was measured from very short relaxation times in afterglow up to the saturation region (determined by cosmic rays and natural radioactivity level) and was explained by the charged particle decay and after that, by surface recombination of nitrogen atoms present as impurities. [26] This was recently confirmed by introducing a controlled quantity of nitrogen impurities into argon in a pulsed radio frequency atmospheric pressure glow discharge.…”

Molecular Dynamics for State‐to‐State Kinetics of Non‐Equilibrium Molecular Plasmas: State of Art and Perspectives

“…It should be noted that results reported in Figure 25 are the consequence of the pumping of vibrational energy in the ground electronic state during atom recombination. They do not take into account the possibility of heterogeneous formation of $A{}^3\Sigma _{\rm u}^ +$ metastable state which plays an important role in the nitrogen afterglow 3, 81…”

Recovery of gas density in a nitrogen gap after breakdown

“…The atoms of nitrogen are known for their ability to store energy over extended periods of time and may recombine on the cathode to produce the initial electrons for the second breakdown. 11 For monoatomic gases such as helium, the long-lived metastable atom He ͑2 3 S͒ is famous for producing electrons by Penning ionization. For gas mixture such as air, it is similar as pure nitrogen that the delayed voltage recovery relative to the recovery of the gas density was also observed.…”