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 the probe increased from 3 to 50 mm. This result agrees with previous measurements in the hot refractory planar anode vacuum arc.