The Switch-On Mechanism of the Current Emission

The switch-on effect of the current emission has been known for long time. This effect consists of the existence of a switch-on voltage, above which current emission from the cathode makes a sudden transition to higher value (one-two orders of magnitude). After the switch-on event, the high current emission status remains even at lower voltages. Our experiments have shown that this switch-on event occurs not only when the voltage (i.e., the cathode electric field) exceeds a certain value, but also occurs applying a relatively low electric field ( $\approx 40$ MV/m) for a long time (tens-hundreds of hours). These transitions are interpreted as changes in the structure of the metal-insulator (MI) potential barrier present, for example, in stainless steel electrodes. This article presents a first characterization of this effect in terms of transition time, current, and voltage level for electrodes made of different materials and/or with different surface treatments. Considerations are finally exposed to explain this switch-on effect as a consequence of the accumulation of electric charge at the MI cathode interface.