Using emissive and non-emissive segmented electrodes to control beam divergence in Hall thrusters

A large plume angle and appreciable fraction of wall losses, typical for Hall thrusters, can be attributed, in part, to a relatively high electron temperature, which is required to sustain effective propellant ionization. Due to lower secondary electron emission, the use of metal channel walls should produce a larger electron temperature than ceramic walls at typical operating conditions of Hall thrusters. However, segmented electrodes placed along a ceramic channel of the thruster are experimentally shown to narrow its plume. Even when segmented electrodes are non-emissive or low emissive, they can still reduce the plume angle, in particular at small mass flow rates. This effect and its dependence on electrode emission capabilities and location are investigated by measuring angular ion flux distribution, plasma potential distribution, thruster performance and emissive spectral characteristics. To facilitate these investigations, a laboratory Hall thruster with segmented electrodes was operated at a vacuum test facility at the PPPL. The thruster utilizes segmented electrodes with the possibility of external heating to control total emission current.