A new design of a single stage, highly effective Hall thruster (2001)

The theoretical maximum efficiency of a modern design single-stage Hall thruster is mainly limited by unnecessary energy loss of electrons in the acceleration zone, and the efficiency usually cannot exceed ~70%. This energy loss is only necessary in order for the electrons that are emitted by the cathode to reach the ionization zone. A way to avoid this loss is proposed; along with a new Hall thruster design concept, which incorporates the innovation. Calculations of the operational characteristics of this new type of thruster show that the maximum efficiency may reach -90%. A simplified variant of the new Hall thruster concept can maintain reduced temperatures in sensitive materials, especially in the magnetic coils and in the channel walls. Other applications of the new Hall thruster concept are discussed in the paper. For example, besides the direct application of producing thrust for spacecraft; the new Hall thruster concept might be used to produce RF power for communication purposes. INTRODUCTION Maximizing the efficiency of a Hall Effect Thruster (HET) used for space missions is an important concern, because the electric power supply is limited. Transitioning between a single stage HET and a double stage Hall thruster is an approach to increasing efficiency; but the increasing technical difficulties and greater complexity make it difficult to realize a practical double stage HET design. For these reasons, the efficiencies of previous experimental double stage HETs are not appreciably better than those of single stage thrusters, for operation with the discharge voltages up to ~ 1000 Volts. No doubt, further development of double stage Hall thrusters will improve their characteristics, including their efficiency; but there will still be a question whether all possibilities to improve single stage HETs have been fully explored. In the paper, we are going to examine an approach to designing an improved single stage HET. NOMENCLATURE v\, ?le, 'Ha efficiency; electron energy efficiency, acceleration zone efficiency; Te electron temperature (energy); O, Ud, Ui? U_ potential, discharge voltage, ionization potential, wave potential; S entropy; Vd, Vz, ue drift, axial, and thermal velocities of electrons; Vj ion velocity; uf, T, A, phase velocity, period, wavelength; d, /a, D channel width, acceleration zone length, thruster diameter; c, m, M speed of light, masses of electrons and ions; E, B electric and magnetic fields; tcb tin, In collision times; interaction of an electron and a wave or motion of an electron through the acceleration zone, azimuthal revolution of an electron; Q, o>e Larmor, plasma frequency; a, e cross-section, electron charge; * Copyright © 2001 by Y. Yashnov, J. McVey, C. McLean, E. Britt, Pratt & Whitney, San Jose. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. * Consultant. * Senior Propulsion Engineer, Member AIAA. § Propulsion Engineer Specialist, Member AIAA. ** Chief Scientist, Member AIAA. American Institute of Aeronautics and Astronautics 1 c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s) Sponsoring Organization. DESCRIPTION OF THE PROBLEM An expression for the efficiency of an ideal single stage Hall thruster (without cathode and coil losses) can be written as: Video! I —— 2U, 1+ aU: (1)