Near-field Ion Current Density Measurements

Faraday probe measurements were taken in the near-field plume of a 6-kW Hall thruster to reduce the negative effects of facility-induced charge-exchange collisions. The results from these measurements were analyzed using a non-standard definition of the current density integration bounds that produced self-consistent beam current and beam divergence values. The measurements indicated a beam divergence half-angle of 16° and an ion beam fraction of 0.78 at the thruster’s nominal operating condition of 300 V and 20 mg/s. These global parameters were used in a probe-based efficiency architecture and the resulting anode efficiency matched thrust stand measurements within 3.2% (absolute not relative). These results represent a marked improvement over traditional far-field Faraday probe measurements that grossly over-predict beam current and beam divergence. Nomenclature CEX = charge-exchange Itot,dyn = dynamic integration beam current DT,mean = thruster mean diameter j = ion current density Ib = ion beam current OR = outer radius Id = discharge current r = radial location IR = inner radius ηb = current utilization Itot = total integrated beam current ηd = divergence utilization Itot,DC = discharge channel beam current θ = divergence half angle