Enhancement in ion beam current with layered-glows in a constricted dc plasma ion source

High current mode has been discovered and investigated in a constricted dc plasma ion source. As discharge currents exceed a certain threshold, voltage to sustain the constricted dc plasma suddenly falls down to almost half of the value. In this sense, constricted dc plasmas can be sustained at much higher current than in conventional mode operation at a fixed discharge voltage. Phenomenally, several discrete layered-glows are created between an anode glow and a cathode glow. The layers are thin and divided by dark spaces where charged particles can be accelerated. In this high current mode, ion beam current density is about 100 times higher than in conventional mode at the same voltage. It is noteworthy that lower gas pressure is desirable to sustain the layered-glow mode, which is also profitable for ion source in terms of differential pumping. Ion current density exceeds 300 mA/cm(2) at low discharge power of 175 W where ion density of plasma ball is estimated to be over 3.7x10(12) cm(-3).