Comment on ‘Coincident ion acceleration and electron extraction for space propulsion using the self-bias formed on a set of RF biased grids bounding a plasma source’

Abstract

Abstract The neutralizer-free ion thruster based on radio frequency (RF) acceleration was proposed as an attractive approach. This comment presents problems arising from such RF acceleration. Two mayor limitations in developing the neutralizer-free RF ion thruster into a practical technology are found to be involved with the grounded grid: (a) the high frequency bias required by low ion impingement from the upstream; (b) serious backstreaming of electron due to the grounded grid that cannot establish a potential barrier. Limitation (a) will degrade the ion production efficiency and cause more serious thermal deformation of the biased grids, especially for large-sized RF ion thrusters. Limitation (b) is the Achilles’ heel of a neutralizer-free RF-biased ion thruster: it in fact operates from the very beginning in the failure mode occurring in the final stage of seriously-eroded DC (direct current) biased ion thruster. The backstreaming electrons will substantially reduce the lifetime of neutralizer-free RF ion thrusters. In the current stage, the RF acceleration is not a promising neutralizer-free technology.