Kinetics of ions and neutral active states in the afterglow and their influence on the memory effect in nitrogen at low pressures

Abstract

The influence of positive ions and neutral active states on the memory effect in nitrogen-filled discharge tubes at 1.3 and 4.0 mbar pressures has been investigated. Analysing the thermal velocity of these particles as well as drift velocity of positive ions, it is shown that the positive ions have a dominant role in the breakdown initiation for afterglow periods lower than 30 ms, while the role of the neutral active states can be ignored because of their electrical neutrality. The estimated value of the positive ion recombination time in the afterglow for the pressures considered is about 30 ms. The atoms in ground states have a dominant role in breakdown initiation for afterglow periods higher than 30 ms. Our supposition is based on the earlier results that the long-lived Lewis–Rayleigh glow lasts up to several hours as a consequence of the recombination of these atoms on the wall. A detailed analysis of relaxation processes has shown that a contribution of vibrationally excited molecules as well as atomic and molecular metastable states created during the previous discharge cannot contribute to the memory effect significantly. Also, the contribution of cosmic rays to memory effect is analysed for the afterglow periods when the concentration of atoms in the ground state decreases to such a low value that their role in the secondary electron emission from the cathode is ignored.

Experimental Investigation of Breakdown Voltage and Electrical Breakdown Time Delay of Commercial Gas Discharge Tubes

“…21) Because the concentration of those particles is considerable, their mutual collision leads to the formation of positive ions. The calculated value of positive ions drift velocity 22) for the applied voltage of U w ¼ 310 V is about 10 6 cm/s and it is two orders of magnitude higher then their thermal velocity. This means that t d depends on ion drift toward the cathode, electron acceleration toward the anode and electron multiplication.…”

Modelling of time delay of electrical breakdown for nitrogen-filled tubes at pressures of 6.6 and 13.3 mbar in the increase region of the memory curve

“…in the plateau and in the region of sudden increase in t d values. Previous experimental data in nitrogen [16,17] have shown that the memory curve consists of three regions: (1) the plateau region (t d insignificantly depends on τ ), (2) the region of sudden rise in t d with the increase in τ , as can be seen in figures 1 and 2, and (3) the saturation region when t d changes insignificantly. It has been concluded that this behaviour of the memory curve is a consequence of different mechanisms which predominantly influence the SEE process.…”

“…Because the energies of some neutral active particles in nitrogen are higher than the cathode material work function, they can release secondary electrons in collision with the metal cathode. The secondary electron emission from the cathode (the SEE process) due to the bombardment of the cathode surface with positive ions and N( 4 S) atoms has an important role in the initiation of breakdown in nitrogen-filled tubes at low pressures, which can be monitored by the time delay method [16,17]. The method consists of acquiring the t d = f (τ ) dependence, also called the memory curve, where t d is the mean value of total time delays t d , i.e.…”

Investigation of the effect of additional electrons originating from the ultraviolet radiation on the nitrogen memory effect

“…The efficiency of neutral active particles in causing the process of secondary electron emission is much smaller than in the case of positive ions, causing the value of t d rapidly increased in relation to the plateau memory curve. Earlier investigations [1], [3], [24], [30] confirmed that the nitrogen atoms in ground state N( 4S) remaining from the previous discharge as well as formed after the discharge ceased are the most responsible particle for the secondary electron emission from the cathode in late nitrogen afterglow. Numerical models, which followed the decrease of nitrogen atoms concentration based on the re-association on the tube walls [3], [4], [24] combined with a model predicts that secondary electron emission is caused by nitrogen atoms, showed a good agreement with the experimental obtained memory curves in the area of sudden increase in t d value.…”