ID-HALL, a new double stage Hall thruster design. I. Principle and hybrid model of ID-HALL

Abstract

In Hall thrusters, ions are extracted from a quasineutral plasma by the electric field induced by the local drop of electron conductivity associated with the presence of a magnetic barrier. Since the electric field is used both to extract and accelerate ions and to generate the plasma, thrust and specific impulse are not independent in a Hall thruster. There is a need for versatile thrusters that can be used for a variety of maneuvers, i.e., that can operate either at high thrust or at high specific impulse for a given power. The double stage Hall thruster (DSHT) design could allow a separate control of ionization and acceleration, and hence separate control of thrust and specific impulse. In the DSHT configuration, a supplementary plasma source (ionization stage), independent of the applied voltage, is added and placed upstream of the magnetic barrier (acceleration stage). The DSHT concept is also well adapted to the use of alternative propellants, lighter and with a less efficient ionization than xenon. Several designs of double stage Hall thrusters have been proposed in the past, but these attempts were not really successful. In this paper, we present a brief review of the main DSHT designs described in the literature, we discuss the relevance of the DSHT concept, and, on the basis of simple physics arguments and simulation results, we propose a new design, called ID-HALL (Inductive Double stage HALL thruster). In this design, the ionization stage is a magnetized inductively coupled RF plasma. The inductive coil is inside the central cylinder of the thruster and located nearby the acceleration stage. Preliminary modeling results of this DSHT are described.

Experimental characterization of ID-Hall, a double stage Hall thruster with an inductive ionization stage

“…Under some conditions, a potential drop may form in this region because of the smaller electron mobility, leading to a plasma potential lower than the anode potential and to the lowering the maximum ion energy at exhaust. The presence of such potential drop in the anode region in single stage operation has been already predicted in simulations of ID-Hall using the hybrid model HALLIS 9,19 .…”

“…A schematic of the ID-Hall design and its magnetic field is shown in figure 1. The magnetic field configuration of this prototype is slightly different from those used in previous simulations 9 , due to the use of ferrites in the RF source instead of soft iron. The use of ferrites prevents the appearance of eddy currents in the magnetic circuit and therefore reduces the power losses.…”

“…The concept of DSHT could also be useful for operation of the thruster with alternative propellants more difficult to ionize than xenon (krypton, argon, air breathing thrusters). A variety of double stage Hall thruster designs have been proposed [1][2][3][4][5][6][7][8] but the relevance of the concept has not really been demonstrated 9 . The ion extraction area of a Hall thruster is much smaller than that of a gridded thruster so that efficient confinement of the plasma in the ionization stage and plasma generation as close as possible to the acceleration region are essential aspects of an efficient DSHT (the effective wall loss area in the ionization stage, taking into account magnetic confinement, should be small with respect to the channel extraction area).…”

“…The ion extraction area of a Hall thruster is much smaller than that of a gridded thruster so that efficient confinement of the plasma in the ionization stage and plasma generation as close as possible to the acceleration region are essential aspects of an efficient DSHT (the effective wall loss area in the ionization stage, taking into account magnetic confinement, should be small with respect to the channel extraction area). We have recently introduced a new design of DSHT, called ID-Hall [9][10][11] (for Inductively coupled Double stage Hall thruster, patent pending) where the ionization stage is a magnetized RF inductively coupled plasma source with an RF coil inside the inner cylinder of the thruster (figure 1). The dimensions of the first experimental prototype of ID-Hall described here are such that the thruster can operate at a total power below 300-400 W. In this paper we present an experimental characterization of ID-Hall operating in single stage and double stage regimes.…”

“…To help explaining the origin of this modulation of the IEDF in the presence of the breathing mode, we used a theoretical model of ID-Hall using the simulation software HALLIS. This software has already been used to estimate the performance and the relevance of the concept of ID-Hall 9 . Here we make only a brief introduction to HALLIS; a more detailed description of HALLIS can be found in Ref.…”