Influence of adsorbed gases on prebreakdown currents in vacuum

It is demonstrated that ions released from adsorbed layers on the anode by field emission electrons change the emitting properties of a well-conditioned cathode, if the current density at the anode is small. If the field emission current density at the anode is greater than 10 A m −2 , as is the case for plane-parallel electrodes with the anode as high-voltage electrode, no change could be measured. For point-hemisphere electrodes (for which the field emission current density at the anode is much less than 10 A m −2 ) it is suggested that surface migration as a result of ion bombardment is responsible for the alterations in the emitting properties of the cathode.