Ion emission from a hollow-cathode discharge with the plasma penetrating into the high-voltage acceleration gap

The general features of ion emission from a gas-discharge plasma are considered under conditions such that the plasma penetrates into the acceleration gap. It is found that the wall sheath limiting the open plasma surface substantially affects the stability of the penetrating plasma. It is shown that there are two plasma states with different positions of the plasma boundary. The stable state corresponds to the inequality r/R > 0.54, where r is the plasma radius in the accelerating electrode and R is the radius of the aperture of the accelerating electrode. It is shown that the plasma-sheath system within the aperture of the accelerating electrode can exist only if the voltage drop across the sheath does not exceed a certain limiting voltage, which depends on the plasma parameters.