Cu Ion Current Measurements in a Vacuum Arc With a Black Body Electrode Configuration

The ion current ejected from a vacuum arc black body assembly (VABBA) with a Cu cathode is studied. In the VABBA, cathode material is emitted into a closed volume formed by a water-cooled cylindrical cathode and a cup-shaped W or Ta anode heated by the arc. If this volume is filled with a dense plasma when anode is hot, it acts as a black body toward macroparticles while a directed plasma jet is emitted through a single small anode aperture or a shower head aperture array. Arc currents are $I=150\hbox {--}300~{\rm A}$ and arc time 120 s. The ion current density $J_{i}$ is measured by an electrical probe. By inserting the probe through a single 4-mm hole in the Ta anode, it is found that $J_{i}$ in the closed volume increased with $I$ from ${\sim}{\rm 5.7}~{\rm A}/{\rm cm}^{2}$ at $I=150~{\rm A}$ , to 18.4 ${\rm A}/{\rm cm}^{2}$ at $I=225~{\rm A}$ . The plasma density is estimated to be ${\sim}10^{15}\hbox {--}10^{16}~{\rm cm}^{-3}$ inside the closed volume. Outside of a W shower head anode with 250 holes with 1-mm diameter in a 200-A arc, the peak $J_{i}$ in the axial direction decreased from ${\sim}{\rm 0.3}$ to ${\sim}{\rm 0.12}~{\rm A}/{\rm cm}^{2}$ when the distance from the anode to th- probe increased from 3 to 50 mm. This result agrees with previous measurements in the hot refractory planar anode vacuum arc.