Long tube discharge evolution to steady state

Summary form only given, as follows. Many processes must occur for a long discharge tube to transition from an insulating gas to an equilibrium DC discharge. By interpreting current and voltage waveforms, initial electron production statistics have been measured for UV irradiated refractory metal cathodes in >5 cm long, 5 mm ID rare gas filled discharge tubes. After initial electron production, the glass wall near the cathode charges up and the resulting plasma propagates from cathode to anode followed by a return stroke propagating from anode to cathode. Using spatially and temporally resolved optical observations, plasma propagation velocities between cathode and anode have been observed for voltages <1000 V and for 5 to 100 Torr fill gas pressures. Once a plasma of sufficiently high conductivity has joined cathode to anode, the positive column electric field quickly reaches steady state values, but the plasma density in the cathode region takes several ambipolar diffusion times before a steady state cathode fall is attained. Using a moving anode technique, time dependent positive column fields and cathode fall voltages will be presented for various pressures from 5 to 500 Torr. Generalizations will be discussed concerning the transition between the initial electron production/avalanche formation, axially directed plasma propagation and cathode plasma density production.