absorbed at the inner surfaces thereof if the ionization rate is sufficient new plasma 60 connected to the initial plasma 32 which is inside the cathode reservoir 34 is generated in this way the front of the plasma 60 propagates along the tube 72 i e a self supporting plasma ionization wave is developing as found experimentally the wave carries nearly the entire cathode potential the plasma column inside the tube 72 behind the ionization front is nearly electric field free and the potential at the front of the column is close to the cathode potential the tube 72 supports the wave propagation since it provides gas atoms for surface ionization and also restricts losses of the plasma electrons once the wave reaches the tube exit 56 the ionization rate drops due to a 3 dimensional escape of the tube plasma electrons and the lack of the surface ionization plasma propagation stops and spatially stationary plasma front 76 forms the plasma is dynamically supported by a weak current due to electron emission from the front at a low gas pressure generally lower than 0 1 pa this state of discharge with high negative potential existing at the tube exit 56 may last for an extended period of time which may last up to several microseconds before a breakdown that is a sharp increase in the discharge current occurs at higher pressure the delay time before breakdown decreases to lower than 10 ns the breakdown between the tube exit plasma which acts as a negative electrode and an anode which is any grounded electrode for instance chamber.