http://mwalker.gatech.edu/papers/ProgAerospace_Singh_V75_2015_pp15-25.pdf

A review of research in low earth orbit propellant collection

The helicon Hall thruster is a two-stage thruster that was developed to investigate whether a radio frequency ionization stage can improve the overall efficiency of a Hall thruster operating at high thrust and low specific impulse. This paper describes an experiment that measured the single-stage and two-stage performance of the helicon Hall thruster operating at 10–25  mg/s anode mass flow rates of xenon at 100–200 V discharge voltages, and also for 6  mg/s of argon at 300 V, and 2.6  mg/s of nitrogen at 200 V. The helicon Hall thruster performance during operation with argon and nitrogen is characterized by low beam divergence efficiency and low propellant utilization efficiency. During two-stage operation, the thrust of the helicon Hall thruster marginally increased with radio frequency power, but the propulsive efficiency and thrust-to-power both decreased with increasing radio frequency power. Probe diagnostics suggest that gains were realized by a slight increase in propellant efficiency, but that t...

/pdf/performance-of-a-helicon-hall-thruster-operating-with-xenon-35qyeh1hef.pdf

Performance of a Helicon Hall Thruster Operating with Xenon, Argon, and Nitrogen

Variable plasma jet velocity with low beam divergence over a range of mass flow rates can be achieved through segmented electrode operation of Hall plasma accelerator. With the use of just a cathode side electrode at the cathode potential, the beam divergence can be decreased substantially, at some cost in efficiency. However, the additional use of an anode side electrode retains the same reduced plume divergence, but at efficiencies comparable to the non-segmented operation. The high efficiency persists also when the anode side electrode is biased at an intermediate potential, thus producing two-stage Hall accelerator operation.

/pdf/variable-operation-of-hall-thruster-with-multiple-segmented-44816cgpfs.pdf

Variable operation of Hall thruster with multiple segmented electrodes

The T-220HT is a 10-kW class Hall effect thruster developed as the primary propulsion system for satellites. In-channel electrodes and additional magnetic coils are added to study ion focusing to decrease energy losses from ion-wall neutralization and plume divergence in order to increase the thrust-to-power ratio. In this study, electrically-biased graphite electrode rings are embedded in the discharge channel walls to repel radial ions. The thruster is tested from 125-300 V at 9 A discharge, with the electrodes either floating, biased to 10 V or 30 V. The mass flow rate was varied from 9.8-10.4 mg/s to maintain constant current. Maximum chamber pressure was 1.5e-5 Torr-Xe. Performance measurements on xenon show a maximum increase in thrust-to-power ratio of 4.84 mN/kW, 15.3 mN thrust, 206 s Isp, and 8% anode efficiency. The plume ion current density, ion energy distribution function, and plasma potential is characterized and indicates a collimation of the ion beam and a increase in ion number density without an increase in propellant neutrals, which results in an increase in mass utilization. The different electrode currents and ion energy distribution functions at 10 V compared to 30 V electrodes leads to the idea of different modes of operation with different electrode biases.

http://mwalker.gatech.edu/papers/JPC_2011_Xu.pdf

Plume Characterization of an Ion Focusing Hall Thruster

The effects of anode temperature on the performance of a 4.5 kW Hall-effect thruster are investigated. The approach separates the location of gas injection from discharge current collection using an anode band, which removes the main mechanism that heats the gas distributor. A thermal model predicts a 270 K reduction of the gas distributor temperature, which corresponds to a 28% increase in the propellant residence time. Collection of the discharge current on the anode band, which is upstream of the bulk Hall current region, generates a 10% increase in ion current density at the thruster centerline for discharge voltages of 100, 125, and 150 V at a xenon mass flow rate of 5  mg/s. The initial reduction in neutral velocity with the anode band is counteracted by the influence of the channel wall temperature, which increases the neutral velocity of the particles by up to 25% greater than the velocity at the gas distributor exit plane. This reduces the potential thruster efficiency improvement from 5.5 to 2.5...

/pdf/propellant-thermal-management-effect-on-neutral-residence-4ved20wxn4.pdf

Propellant Thermal Management Effect on Neutral Residence Time in Low-Voltage Hall Thrusters

The Helicon Hall Thruster (HHT) development program seeks to achieve high efficiency operation of a high-thrust, low-specific impulse (Isp) Hall thruster by employing the efficient ionization mechanism of a helicon source while maintaining the efficient acceleration characteristics which have made Hall thrusters an attractive propulsion option. In the HHT, ions are created in an annular helicon first stage and then accelerated in a closed-drift, Hall-effect second stage. Helicon waves, which are cylindrically bounded whistler waves, are considered to be one of the most efficient methods of producing a high-density, low-temperature plasma. A decrease in the power required for propellant ionization will directly translate into an increase in thruster efficiency at non-nominal Hall thruster operating conditions. This paper will present the work done to date on the HHT performance evaluation for input power from 0.6 to 8 kW with discharge voltages ranging from 100 to 600 V and discharge currents ranging from 5 to 25 A. Results of the performance characterizations suggest that there is a possible advantage of a Hall thruster with RF ionization stage at increasing RF-power.

Raymond Liang

Papers

Performance and Plume Characterization of a Helicon Hall Thruster