Abstract:
Erosion characteristics on the cover of the inner front pole in a 12.5 kW Hall thruster
were measured over a wide range of operating conditions in tests of 6 to 14 hours duration
using an accelerated test method and a very sensitive radioactive tracer-based erosion
diagnostic. The operating points included the nominal 300 - 600 V conditions on a
constant 20.8 A throttle curve, but included additional conditions at other currents
spanning the throttling envelope and measurements at varying magnetic eld strength,
facility pressure, and discharge voltage oscillation amplitude. The results show that the
300 V condition produces the highest wear rates on the 20.8 A throttle curve, but that
rates actually increase with decreasing current. The wear rate was insensitive to discharge
voltage ripple, but increased monotonically with magnetic eld strength, particularly near
the inner radius of the pole cover. The inner region was also sensitive to facility pressure,
showing lower rates at a higher pressure level. Separate experiments in which the energy
distributions of ions generated by the hollow cathode were measured suggest that the
cathode plume may be a source of energetic ions responsible for some of the erosion
trends, in addition to ions originating in the thruster plume. The Hall thruster simulation
code Hall2De is able to reproduce the erosion characteristics observed at 600 V, 20.8 A,
but cannot currently match the rates measured at lower voltages and currents.
