Analysis of neutral active particle loss in afterglow in krypton at 2.6mbar pressure

Abstract

This paper presents the analysis of the surface recombination and/or de-excitation of neutral active particles in two different volume krypton-filled tubes at pressure of 2.6mbar with 1ppm oxygen impurities. The analysis was performed on the basis of secondary electron emission from the cathode induced by positive ions and neutral active particles using the experimental data of electrical breakdown time delay mean value td¯ as a function of afterglow period τ (“memory curve”). It was shown that the main channel of neutral active particles' loss in afterglow is their recombination and/or de-excitation on the bulb walls. The loss rate increases with the increase of available wall surface per unit of gas volume. It was also shown that in early afterglow (15ms for the tube with smaller bulb volume and 30ms for the tube with bigger bulb volume) positive ions are formed in the mutual collisions of neutral active particles, and these ions dominantly influence the secondary electron emission from the cathode. In late afterglow (to 30s for the tube with smaller bulb volume and to 150s for the tube with bigger bulb volume) neutral active particles have dominant role in secondary electron emission from the cathode. The probability for this process decreases with the increase of afterglow period as a consequence of the decrease of the concentration of neutral active particles in gas, and this probability is smaller for the tube with smaller bulb volume. The influence of additional electron yield in the electrode gap caused by gamma radiation on breakdown initiation is also analyzed. It is shown that the influence of the neutral active particles in the process of secondary electron emission in the case of gamma radiation is also significant in both early and late afterglow.