The Stanford Diverging Cusped Field Thruster: Design, Construction, and Initial Testing

The design and initial characterization of a cylindrical diverging cusped field (DCF) thruster is presented. The thruster operates with krypton propellant at power levels ranging from 25-250 W. Thrust, specific impulse, and thrust (anode) efficiency are found to be very sensitive to cathode placement, and thrust efficiencies exceeding 20% are found over a range of operating conditions. The discharge current shows that this thruster is quiet, displaying none of the periodic oscillations seen in typical Hall thrusters. Plume ion current measurements indicate the existence of a conical ion emission, similar to that seen previously in a model with diverging channel walls; this suggests that the ion divergence of the plume is more closely connected to the magnetic field topography than the channel geometry.

When operating with 300 V to the anode, plasma potential measurements throughout the near-field reveal regions of elevated plasma potential (in some places exceeding 100 V) that are coincident with the most luminous visible regions of the discharge and peaks in ion current density. Channel potential measurements show that a significant potential increase (from 12% to 88% of anode potential) occurs within a few millimeters around the exit plane, also corresponding to a bright visible plasma region. Electron temperature is shown to peak along the thruster axis (in some areas over 10 eV).

Preliminary results of a kinetic electron simulation based on experimental potential data are also presented. The high magnetic field strengths cause electrons to move in tight helical orbits and undergo several mirroring events. Thus far, test electrons released in the near-field fail to reach the channel, while test electrons released along the thruster axis remain confined to the channel, sometimes reaching the anode.