Ionization Waves Initiating Single-Electrode Breakdown in Long Discharge Tubes

Ionization waves (IWs) of positive polarity are studied experimentally in several sealed discharge tubes containing neon at pressures of 0.6‒15 Torr and surrounded with a grounded metal screen. The IWs arise at the stage single-electrode breakdown development at moderate overvoltage conditions, and belong to “slow” ionization waves (velocity of 10⁵‒10⁸ cm/s). The wave propagation is accompanied by a monotonic loss of velocity and the electric potential magnitude at the IW front, indicating its significant spatial attenuation. The IWs are studied by recording x‒t diagrams supplemented with measurements of instantaneous velocities, front potentials, and attenuation coefficients at various pressures and applied voltages. An exponential nature of a decrease in the front potential and instantaneous velocity of the IWs with the distance traveled is established. It is found that the scales of the exponential decrease in both quantities do not coincide. The obtained results can be useful in planning experiments on breakdown in long tubes, ionization wave modeling, as well as their technological implementation