The influence of some species formed during the discharge and gamma and UV radiation on breakdown voltage and time delay in nitrogen and neon at low pressure

The contribution of some neutral active states formed during previous discharge to the breakdown initiation has been analysed in nitrogen and neon at 6.6 mbar pressure on the basis of the time delay mean value (t) over bar (d) as a function of afterglow period tau ('memory curve') and the breakdown voltage mean value (U) over barb as a function of tau. The contribution of Compton's electrons induced by gamma radiation and photoelectrons induced by UV radiation to breakdown initiation has also been studied. It has been shown that in the early afterglow (up to 30 ms) positive ions formed in the collisions between metastable molecules and highly vibrationally excited molecules in nitrogen and positive ions formed in collision between metastable atoms in neon have a dominant role in breakdown initiation. Gamma and UV radiation lead to a decrease in ion concentration in the early afterglow due to recombination of ions with electrons released from the tube walls and electrodes. For tau values from 30 ms up to 7 sin nitrogen, gamma and UV radiation have a negligible influence on the breakdown initiation owing to the presence of a significant concentration of atoms in the ground state in the afterglow and no possibility of creation of positive ions. The influence of gamma radiation on breakdown initiation in neon is insignificant for tau interval from 30 ms to 0.15 s, whereas UV radiation has a significant influence on breakdown initiation for tau > 30 s. When the concentration of neutral active states decreases enough, the breakdown initiation is caused by cosmic rays in the case of non-irradiated tubes and gamma/UV photons in the case of gamma/UV irradiated tubes; this is manifested by the memory curve saturation. The memory curve saturation in the case of irradiated nitrogen and neon-filled tubes occurs at lower tau values than in the case of non-irradiated tubes, and it is a consequence of increased electron yield in the inter-electrode space.