Sensitivity of 30-cm mercury bombardment ion thruster characteristics to accelerator grid design

The design of ion optics for bombardment thrusters strongly influences overall performance and lifetime. The operation of a 30-cm thruster with accelerator grid open area fractions ranging from 43 to 24 percent, was evaluated and compared with previously published experimental and theoretical results. Ion optics properties measured included the beam current extraction capability, the minimum accelerator grid voltage to prevent backstreaming, ion beamlet diameter as a function of radial position on the grid and accelerator grid hole diameter, and the high energy, high angle ion beam edge location. Discharge chamber properties evaluated were propellant utilization efficiency, minimum discharge power per beam amp, and minimum discharge voltage.