Nested Hall thrusters are more than the sum of their parts
DOI: 10.1063/1.5031795
Nested Hall thrusters are more than the sum of their parts lead image
The Hall-effect thruster is a long-proven spaceflight technology, used mostly for low-thrust applications like satellite station-keeping. Nested Hall thrusters (NHTs), in which several thrusters are combined in a coaxial array, demonstrate increased thrust and more versatility, including throttling capability unavailable to traditional single-channel thrusters.
Experiments reported in the Journal of Applied Physics demonstrate that the increased thrust in NHTs, which is actually greater than the sum of the individual channels, chiefly results from a combination of two major factors unique to the nested configuration.
The researchers investigated the mechanisms leading to the increased thrust using an X2 dual-channel type of NHT, testing the operation of each channel both separately and together using different gas injection locations. To ensure that all measurements focused only on local pressure effects, the facility background pressure was kept constant in all operating modes. Using a thrust stand, ion gauge, Faraday probe and laser-induced fluorescence, the researchers measured performance, current density, divergence angle, and the acceleration region.
As local pressure at the thruster increases, they found that the acceleration region shifts upstream, thereby decreasing the beam divergence angle and increasing overall thrust by approximately 9 millinewtons (mN). Additionally, they also showed neutral gas ingestion from the adjacent thruster channel contributed to a thrust increase of about 2.0 mN. While the increase was expected to be the sum, 10.7 ± 1.3 mN, the experimentally measured thrust increase was actually 17 ± 6.2 mN — somewhat larger but still in agreement within the measurement uncertainties.
Other phenomena not considered in these experiments include plasma oscillations and cathode pressure gradients, which may also contribute to the observed synergetic effects. The work provides further evidence of the value NHTs offer to both enhanced thruster performance and compelling design advantages over single-channel Hall thruster arrays.
Source: “On channel interactions in nested Hall thrusters,” by S. E. Cusson, M. P. Georgin, H. C. Dragnea, E. T. Dale, V. Dhaliwal, I. D. Boyd, and A. D. Gallimore, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5028271 .
