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Investigation of the Stationary Plasma Thruster (SPT-100) - Characteristics and thermal maps at the raised discharge power
... Parameter Value Discharge Voltage (V) 300 Mass flow rate (mg/s) 5 Anode temperature (K), [18] [19] ...
... 750 Wall temperature (K), [18] [19] ...
Progress on the development of physics-based modeling tools aimed at predicting the service life of Hall thrusters is discussed. Modifications of the wall sheath and electron mobility models in the hybrid fluid/particle-in-cell computer code HPHall-2 are made and the effects of these changes on the plasma parameters and thruster performance are assessed. The wall sheath model of Hobbs and Wesson [Plasma Physics, 9, 85-87 (1967)] has been adopted, resulting in modifications to the predicted sheath potentials that are relevant to the modeling of high specific impulse Hall thrusters. Experiments with a widely used mixed-mobility model of the cross-field electron transport is presented that enables the simultaneous prediction of thrust and discharge current in agreement with experimental data. Taken together, these code modifications have improved the predictive capability of HPHALL-2 to serve as an input for studies of Hall thruster erosion.
... Neutrals are injected from the inlet that is modelled as an annular ring positioned at the centre of anode wall. Velocities of new-injected particles are sampled from a semi-Maxwellian distribution characterized by anode wall temperature [30]. ...
Hall Effect Thrusters (HETs) are nowadays widely used for satellite applications because of their efficiency and robustness compared to other electric propulsion devices. Computational modelling of plasma in HETs is interesting for several reasons: it can be used to predict thrusters' operative life; moreover, it provides a better understanding of the physical behaviour of this device and can be used to optimize the next generation of thrusters. In this work, the discharge within the accelerating channel and near-plume of HETs has been modelled by means of an axisymmetric hybrid approach: a set of fluid equations for electrons has been solved to get electron temperatures, plasma potential and the discharge current, whereas a Particle-In-Cell (PIC) sub-model has been developed to capture the behaviour of neutrals and ions. A two-region electron mobility model has been incorporated. It includes electron-neutral/ion collisions and uses empirical constants, that vary as a continuous function of axial coordinates, to take into account electron-wall collisions and Bohm diffusion/SEE effects. An SPT-100 thruster has been selected for the verification of the model because of the availability of reliable numerical and experimental data. The results of the presented simulations show that the code is able to describe plasma discharge reproducing, with consistency, the physics within the accelerating channel of HETs. A small discrepancy in the experimental magnitude of ions' expansion, due probably to boundary condition effects, has been found.
... All results in this paper are based on the SPT-100 geometry and magnetic field used previously in Ref. [17].Figure 1 shows the geometry and grid andTable 1 presents some of the basic inputs used for the simulations. We have updated the anode and wall temperatures from those used in Ref. [17] to values found in the literature [22,23]. Modifications specific to code updates, such as the wall accommodation, are discussed later. ...
The primary life-limiting mechanism in Hall thrusters is the erosion of the discharge chamber walls by propellant ions. Although substantial progress has been made in recent years in Hall thruster theory and design, relatively little progress has been made in understanding this life limiting process. The development of this understanding is critically needed if Hall thrusters are to be successfully integrated into NASA science missions. In this paper, we review recent progress of the development of physics-based modeling tools aimed at predicting the service life of Hall thrusters. A channel erosion sub-model developed at the Jet Propulsion Laboratory (JPL) is combined with results from the 2-D hybrid fluid/particle-in-cell computer code HPHall-2 that is used to simulate the plasma and neutral gas inside the discharge chamber and near-plume regions. This paper assesses the impact of the heavy particle velocity and electron mobility models on plasma simulations. It is found that improvements on the velocity condition at the injector boundary and on the gas-surface interaction model for neutrals and ions at wall boundaries leads to neutral speeds and mass utilization efficiencies that are more consistent with experimental values. Simulations using non-classical electron mobility that is wall-dominated inside the channel but Bohm-dominated in the near plume yield more accurate electron temperature and electric field distributions along the channel but at lower values typically obtained in experiments.
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 Vat 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%. The selected downstream location of the anode band results in a 6-10% increase in discharge current compared with current collection on the gas distributor.
During the last decade, electric propulsion systems have been established for orbit maintenance of satellites. More than 150 spacecrafts are now equipped with almost 400 thrusters for this purpose. This decade will see the use of electric propulsion for primary propulsion. The purpose of this paper is to determine optimal mission parameters for these tasks. Depending on the mission profile, ion thrusters, Hall thrusters, thermal arcjets or MPD thrusters are preferable. All electric propulsion systems have in common that they can be operated in a wide range of the specific impulse and that the thrust efficiency and therefore also the specific power of the propulsion system depend strongly on the specific impulse. The optimal specific impulse for a particular mission depends, therefore, on the kind of thruster and the chosen propellant. This paper shows that for MPD, Ion, Hall ion and thermal arcjet thrusters the optimal specific impulse for a particular mission can be determined by an optimization which is based on the rocket equation. Using, in addition, a simple cost function, the influence of the cost factors is explained. Finally, the results for a few missions for which electric propulsion systems for primary propulsion have been selected are discussed. © 2001 by Monika Auweter-Kurtz. Published by the American Institute of Aeronautics and Astronautics,Inc.
Neutral flow dynamics in Hall thrusters are not often regarded as a critical aspect that controls thruster operation and discharge channel physics. This dissertation, combined with previous work, showed that neutral flow dynamics affect global properties including thruster performance, stability, thermal margin, and lifetime. In addition, the neutral flow rate, and more importantly, the electron-neutral collision rate in the channel have an impact on other thruster properties including the location, size, and intensity of the ionization, high electron temperature, and acceleration regions. The results of these findings are relevant to ongoing efforts to understand thruster operation, electron physics, and thruster lifetime.
Performance and plume measurements indicated that thruster efficiency remained constant from ?? 50% of the nominal flow rate of 20 mg/s. Current
utilization was the primary loss mechanism and it decreased with flow rate due to increased ionization losses and electron-wall losses. To compensate, the divergence and mass utilizations increased with flow rate through a more compact ionization region and increased ionization efficiency from the increasing neutral density.
Electron collision frequencies and the electron Hall parameter were calculated from measurements of the ion density, electron temperature, and electric field inside the discharge channel. The peak Hall parameter moved downstream and decreased in magnitude as flow rate was increased, and the results confirmed that there exist at least three distinct electron mobility regions as implemented in some plasma simulations. Near the anode, the turbulence was approximated by the Bohm value. Near the channel exit, the turbulence was suppressed and electrons were most effectively trapped by the Hall current in this region. In the plume, the turbulence was an order of magnitude greater than the Bohm value, indicating large contributions to electron transport from turbulence or a currently unaccounted for anomalous transport mechanism. For most of the channel, the electron-neutral collisions were the primary contributor to electron energy loss and cross-field mobility. However, near the channel exit, electron-wall collisions increased and became the primary contributor to the measured decrease in electron temperature with increased flow rate.
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