Investigation of the extracted h current in a continuously pulsed-volume negative-ion source

We have observed a significant increase in average extracted negative-ion current (I^‒) when pulsing the discharge current of a small, high-power density volume negative-ion source at low pressures. Compared to a DC-operated discharge, (I^‒) is increased by 35% at a pressure of 0.38 Pa. This result is explained with a simple model which shows that the enhancement of (I^‒) at low pressures can be attributed to an increased production of negative ions through dissociative attachment, as a result of the colder electrons in the postdischarge. The temporal behaviour of the extracted negative-ion current in this small, high-power density source is markedly different than the negative-ion current of a larger low-power density source.