Dependence of the Breakdown Potential on the Voltage Rise Rate in a Long Discharge Tube at Low Pressure

We have measured the dynamic breakdown voltage in a long (80 cm) discharge tube in neon, argon, their mixture, and in argon with mercury vapor at pressures of 80-400 Pa in a wide range of anode voltage rise rates (dU/dt 10(-4)-10(2) kV/ms). We have detected a nonmonotonic dependence of the breakdown voltage on dU/dt with a minimum in the region 0.1-10 kV/ms. The breakdown voltage rise in the range of low voltage growth rate can probably be explained by the specific features of breakdown in long tubes and is associated with the accumulation of a surface charge on the tube walls. The charge reduces the potential difference between the anode and the wall and complicates the primary breakdown between them. The results of additional experiments with pulses superimposed on a constant bias voltage confirm the admissibility of such an explanation.