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Nathaniel J. Fisch - One of the best experts on this subject based on the ideXlab platform.
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Effect of Magnetic Shielding on Plasma Plume of the Cylindrical Hall Thrusters
2011Co-Authors: Yevgeny Raitses, Jean Carlos Gayoso, Nathaniel J. FischAbstract:The cylindrical Hall thruster with permanent magnets produces a plasma plume with an unusual halo shape of the angular ion current distribution. The addition of the magnetic shield to the thruster magnetic circuit causes the plume shape to change to a conic type with the maximum ion current at the centerline. This is a typical plume shape for conventional annular Hall Thrusters and the cylindrical Hall Thrusters with electromagnet coils. Plasma potential measurements revealed that without the magnetic shield, a significant part of the acceleration region (~ 50%) is located outside the permanent magnet thruster. In this outside region, the magnetic field is strong, 100-300 Gauss. The reduction of the outside magnetic field with the magnetic shield causes the acceleration region to shift inside the thruster channel. In addition to the change of the plume shape, this process is accompanied with a significant plume narrowing. Experiments with a magnetically shielded configuration of a cylindrical Hall thruster with electromagnet coils demonstrate a complex dependence of the plume shape on the magnetic field topology.
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Cylindrical Hall Thrusters with Permanent Magnets
Journal of Applied Physics, 2010Co-Authors: Yevgeny Raitses, E. Merino, Nathaniel J. FischAbstract:The use of permanent magnets instead of electromagnet coils for low power Hall Thrusters can offer a significant reduction in both the total electric power consumption and the thruster mass. Two permanent magnet versions of the miniaturized cylindrical Hall thruster (CHT) of different overall dimensions were operated in the power range of 50–300 W. The discharge and plasma plume measurements revealed that the CHT Thrusters with permanent magnets and electromagnet coils operate rather differently. In particular, the angular ion current density distribution from the permanent magnet Thrusters has an unusual halo shape, with a majority of high energy ions flowing at large angles with respect to the thruster centerline. Differences in the magnetic field topology outside the thruster channel and in the vicinity of the channel exit are likely responsible for the differences in the plume characteristics measured for the CHTs with electromagnets and permanent magnets. It is shown that the presence of the reversin...
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Plasma Plume of Annular and Cylindrical Hall Thrusters
IEEE Transactions on Plasma Science, 2008Co-Authors: Nathaniel J. Fisch, Yevgeny RaitsesAbstract:Hall Thrusters hold considerable advantage over chemical Thrusters and other kinds of electrical propulsion devices, except that the plume of the Hall thruster tends to be wide. An ongoing objective in Hall-thruster research is to narrow this plume. The plume is sensitive both to the specific geometry of the magnetic field as well as to the voltage potential induced within the plasma. Annular-geometry Hall Thrusters tend to have narrower plumes. However, the cylindrical-geometry thruster has been shown to be suited particularly to low-power operation. New techniques have been advanced to narrow the Hall-thruster plumes. In this paper, images of the plasma plume in the two geometries of the Hall thruster are presented.
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Optimization of Cylindrical Hall Thrusters
43rd AIAA ASME SAE ASEE Joint Propulsion Conference & Exhibit, 2007Co-Authors: Yevgeny Raitses, Artem Smirnov, Erik Granstedt, Nathaniel J. FischAbstract:The cylindrical Hall thruster features high ionization efficiency, quiet operation, and ion acceleration in a large volume-to-surface ratio channel with performance comparable with the state-of-the-art annular Hall Thrusters. These characteristics were demonstrated in low and medium power ranges. Optimization of miniaturized cylindrical Thrusters led to performance improvements in the 50-200W input power range, including plume narrowing, increased thruster efficiency, reliable discharge initiation, and stable operation.
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Enhanced Performance of Cylindrical Hall Thrusters
Applied Physics Letters, 2007Co-Authors: Yevgeny Raitses, A. Smirnov, Nathaniel J. FischAbstract:The cylindrical thruster differs significantly in its underlying physical mechanisms from the conventional annular Hall thruster. It features high ionization efficiency, quiet operation, ion acceleration in a large volume-to-surface ratio channel, and performance comparable with the state-of-the-art conventional Hall Thrusters. Very significant plume narrowing, accompanied by the increase of the energetic ion fraction and improvement of ion focusing, led to 50%–60% increase of the thruster anode efficiency. These improvements were achieved by overrunning the discharge current in the magnetized thruster plasma.
Yevgeny Raitses - One of the best experts on this subject based on the ideXlab platform.
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Effect of Magnetic Shielding on Plasma Plume of the Cylindrical Hall Thrusters
2011Co-Authors: Yevgeny Raitses, Jean Carlos Gayoso, Nathaniel J. FischAbstract:The cylindrical Hall thruster with permanent magnets produces a plasma plume with an unusual halo shape of the angular ion current distribution. The addition of the magnetic shield to the thruster magnetic circuit causes the plume shape to change to a conic type with the maximum ion current at the centerline. This is a typical plume shape for conventional annular Hall Thrusters and the cylindrical Hall Thrusters with electromagnet coils. Plasma potential measurements revealed that without the magnetic shield, a significant part of the acceleration region (~ 50%) is located outside the permanent magnet thruster. In this outside region, the magnetic field is strong, 100-300 Gauss. The reduction of the outside magnetic field with the magnetic shield causes the acceleration region to shift inside the thruster channel. In addition to the change of the plume shape, this process is accompanied with a significant plume narrowing. Experiments with a magnetically shielded configuration of a cylindrical Hall thruster with electromagnet coils demonstrate a complex dependence of the plume shape on the magnetic field topology.
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Cylindrical Hall Thrusters with Permanent Magnets
Journal of Applied Physics, 2010Co-Authors: Yevgeny Raitses, E. Merino, Nathaniel J. FischAbstract:The use of permanent magnets instead of electromagnet coils for low power Hall Thrusters can offer a significant reduction in both the total electric power consumption and the thruster mass. Two permanent magnet versions of the miniaturized cylindrical Hall thruster (CHT) of different overall dimensions were operated in the power range of 50–300 W. The discharge and plasma plume measurements revealed that the CHT Thrusters with permanent magnets and electromagnet coils operate rather differently. In particular, the angular ion current density distribution from the permanent magnet Thrusters has an unusual halo shape, with a majority of high energy ions flowing at large angles with respect to the thruster centerline. Differences in the magnetic field topology outside the thruster channel and in the vicinity of the channel exit are likely responsible for the differences in the plume characteristics measured for the CHTs with electromagnets and permanent magnets. It is shown that the presence of the reversin...
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Plasma Plume of Annular and Cylindrical Hall Thrusters
IEEE Transactions on Plasma Science, 2008Co-Authors: Nathaniel J. Fisch, Yevgeny RaitsesAbstract:Hall Thrusters hold considerable advantage over chemical Thrusters and other kinds of electrical propulsion devices, except that the plume of the Hall thruster tends to be wide. An ongoing objective in Hall-thruster research is to narrow this plume. The plume is sensitive both to the specific geometry of the magnetic field as well as to the voltage potential induced within the plasma. Annular-geometry Hall Thrusters tend to have narrower plumes. However, the cylindrical-geometry thruster has been shown to be suited particularly to low-power operation. New techniques have been advanced to narrow the Hall-thruster plumes. In this paper, images of the plasma plume in the two geometries of the Hall thruster are presented.
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Optimization of Cylindrical Hall Thrusters
43rd AIAA ASME SAE ASEE Joint Propulsion Conference & Exhibit, 2007Co-Authors: Yevgeny Raitses, Artem Smirnov, Erik Granstedt, Nathaniel J. FischAbstract:The cylindrical Hall thruster features high ionization efficiency, quiet operation, and ion acceleration in a large volume-to-surface ratio channel with performance comparable with the state-of-the-art annular Hall Thrusters. These characteristics were demonstrated in low and medium power ranges. Optimization of miniaturized cylindrical Thrusters led to performance improvements in the 50-200W input power range, including plume narrowing, increased thruster efficiency, reliable discharge initiation, and stable operation.
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Enhanced Performance of Cylindrical Hall Thrusters
Applied Physics Letters, 2007Co-Authors: Yevgeny Raitses, A. Smirnov, Nathaniel J. FischAbstract:The cylindrical thruster differs significantly in its underlying physical mechanisms from the conventional annular Hall thruster. It features high ionization efficiency, quiet operation, ion acceleration in a large volume-to-surface ratio channel, and performance comparable with the state-of-the-art conventional Hall Thrusters. Very significant plume narrowing, accompanied by the increase of the energetic ion fraction and improvement of ion focusing, led to 50%–60% increase of the thruster anode efficiency. These improvements were achieved by overrunning the discharge current in the magnetized thruster plasma.
Alec D Gallimore - One of the best experts on this subject based on the ideXlab platform.
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On channel interactions in nested Hall Thrusters
Journal of Applied Physics, 2018Co-Authors: Sarah E. Cusson, Iain D. Boyd, Marcel P. Georgin, Horatiu C. Dragnea, Ethan T. Dale, Vira Dhaliwal, Alec D GallimoreAbstract:Nested Hall Thrusters use multiple, concentric discharge channels to increase thrust density. They have shown enhanced performance in multi-channel operation relative to the superposition of individual channels. The X2, a two-channel nested Hall thruster, was used to investigate the mechanism behind this improved performance. It is shown that the local pressure near the thruster exit plane is an order of magnitude higher in two-channel operation. This is due to the increased neutral flow inherent to the multi-channel operation. Due to the proximity of the discharge channels in nested Hall Thrusters, these local pressure effects are shown to be responsible for the enhanced production of thrust during multi-channel operation via two mechanisms. The first mechanism is the reduction of the divergence angle due to an upstream shift of the acceleration region. The displacement of the acceleration region was detected using laser induced fluorescence measurements of the ion velocity profile. Analysis of the chang...
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performance and initial investigation of channel interactions on nested channel Hall Thrusters
International Conference on Plasma Science, 2016Co-Authors: Sarah E. Cusson, Ethan T. Dale, Scott J Hall, Alec D GallimoreAbstract:The University of Michigan, in collaboration with NASA and the Air Force Office of Scientific Research, has developed two nested-channel Hall Thrusters: the X2 and the X3. The X2 is a 6-kW two-channel thruster that was designed as a proof of concept for nesting channels concentrically. The thruster runs off a single centrally-mounted cathode. The successful results of the X2 project lead to the development of the X3, a 200-kW three-channel thruster.
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Rotating Spoke Instabilities in Hall Thrusters
IEEE Transactions on Plasma Science, 2011Co-Authors: Michael Mcdonald, Alec D GallimoreAbstract:High-speed imaging of a Hall thruster plume reveals near-omnipresent rotating regions of elevated light emission, dubbed rotating spokes, in the annular thruster discharge channel. Azimuthal oscillations have long been suggested to induce cross-field electron transport in Hall Thrusters, but conclusive experimental identification of such oscillations with probes is often cHallenging. However, simple processing of high-speed images taken at a few tens of thousands of frames per second clearly reveals long-wavelength rotating spokes at very low frequencies, corresponding to velocities of only a few hundred meters per second.
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Parametric Investigation of the Rotating Spoke Instability in Hall Thrusters
2011Co-Authors: Michael Mcdonald, Alec D GallimoreAbstract:This work presents recent results of ongoing investigations into rotating spoke instabilities in Hall Thrusters. Recent work by the authors demonstrated large amounts of electron current carried by spokes in the nearanode region in the H6 6-kW laboratory model Hall thruster, and raises the question of whether spokes may play a larger role in electron transport throughout the Hall thruster plume. Spokes have since been observed via high speed imaging in several Hall Thrusters, including the H6, the NASA 173Mv1, the X2 dual nested channel Hall thruster, the Helicon Hall thruster, and the Busek BHT-600. While this work focuses on the H6 Hall thruster, visual examples of spoke presence in these other Thrusters are also presented. A parameter study of the dependence of spoke amplitude and propagation velocity on magnetic field strength and discharge voltage in the H6 shows that the magnetic field strength has a strong influence on spoke properties. Spokes appear to be omnipresent in Hall Thrusters, though with widely variable strength and stability, and appear even at very highly efficient operating conditions with high voltage and high magnetic field strength – the most prominent spoke mode in the H6 is observed at a 600 V, 65% total efficiency operating condition. In response to earlier studies that have observed spokes exclusively at low voltage or in inefficient operating regimes, a study of spoke behavior at a very low voltage operating condition links a transition to higher efficiency operation with the formation of stabilized spoke structures. Finally, we present visual evidence from high-speed imaging of spokes bridging the centrally mounted cathode to the discharge channel.
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high specific impulse Hall Thrusters part 1 influence of current density and magnetic field
Journal of Propulsion and Power, 2006Co-Authors: Richard R. Hofer, Robert S. Jankovsky, Alec D GallimoreAbstract:A laboratory-model Hall thruster with a magnetic circuit designed for high-specific impulse (2000‐3000 s) was evaluated to determine how current density and magnetic field affect thruster operation. Results have shown for the first time that a minimum current density and optimum magnetic field shape exist at which efficiency will monotonically increase with specific impulse. At the nominal mass flow rate of 10 mg/s and between discharge voltages of 300 and 1000 V, total specific impulse and total efficiency ranged from 1600 to 3400 s and 51 to 61%, respectively. Comparison with a similar thruster showed how efficiency can be optimized for specific impulse by varying the shape of the magnetic field. Plume divergence decreased from a maximum of 48 deg at 400 V to a minimum of 35 deg at 1000 V, but increased between 300 and 400 V as the likely result of a large increase in discharge current oscillations. The breathing-mode frequency continuously increased with voltage, from 14.5 kHz at 300 V to 22 kHz at 1000 V, in contrast to other Hall Thrusters where a sharp decrease of the breathing-mode frequency was found to coincide with increasing electron current and decreasing efficiency. These findings suggest that efficient, high-specific impulse operation was enabled through the regulation of the electron current with the applied magnetic field.
A. Smirnov - One of the best experts on this subject based on the ideXlab platform.
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Enhanced Performance of Cylindrical Hall Thrusters
Applied Physics Letters, 2007Co-Authors: Yevgeny Raitses, A. Smirnov, Nathaniel J. FischAbstract:The cylindrical thruster differs significantly in its underlying physical mechanisms from the conventional annular Hall thruster. It features high ionization efficiency, quiet operation, ion acceleration in a large volume-to-surface ratio channel, and performance comparable with the state-of-the-art conventional Hall Thrusters. Very significant plume narrowing, accompanied by the increase of the energetic ion fraction and improvement of ion focusing, led to 50%–60% increase of the thruster anode efficiency. These improvements were achieved by overrunning the discharge current in the magnetized thruster plasma.
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space charge saturated sheath regime and electron temperature saturation in Hall Thrusters
Physics of Plasmas, 2005Co-Authors: Yevgeny Raitses, A. Smirnov, David Staack, Nathaniel J. FischAbstract:Existing electron-wall interaction models predict that secondary electron emission in Hall Thrusters is significant and that the near-wall sheaths are space charge saturated. The experimental electron-wall collision frequency is computed using plasma parameters measured in a laboratory Hall thruster. In spite of qualitative similarities between the measured and predicted dependencies of the maximum electron temperature on the discharge voltage, the deduced electron-wall collision frequency for high discharge voltages is much lower than the theoretical value obtained for space charge saturated sheath regime, but larger than the wall recombination frequency. The observed electron temperature saturation appears to be directly associated with a decrease of the Joule heating rather than with the enhancement of the electron energy loss at the walls due to a strong secondary electron emission. Another interesting experimental result is related to the near-field plasma plume, where electron energy balance appears to be independent on the magnetic field.
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space charge saturated sheath regime and electron temperature saturation in Hall Thrusters
Other Information: PBD: 16 Mar 2005, 2005Co-Authors: Yevgeny Raitses, A. Smirnov, David Staack, Nathaniel J. FischAbstract:Secondary electron emission in Hall Thrusters is predicted to lead to space charge saturated wall sheaths resulting in enhanced power losses in the thruster channel. Analysis of experimentally obtained electron-wall collision frequency suggests that the electron temperature saturation, which occurs at high discharge voltages, appears to be caused by a decrease of the Joule heating rather than by the enhancement of the electron energy loss at the walls due to a strong secondary electron emission.
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electron cross field transport in a low power cylindrical Hall thruster
Physics of Plasmas, 2004Co-Authors: A. Smirnov, Yevgeny Raitses, Nathaniel J. FischAbstract:Conventional annular Hall Thrusters become inefficient when scaled to low power. Cylindrical Hall Thrusters, which have lower surface-to-volume ratio, are therefore more promising for scaling down. They presently exhibit performance comparable with conventional annular Hall Thrusters. Electron cross-field transport in a 2.6 cm miniaturized cylindrical Hall thruster (100 W power level) has been studied through the analysis of experimental data and Monte Carlo simulations of electron dynamics in the thruster channel. The numerical model takes into account elastic and inelastic electron collisions with atoms, electron-wall collisions, including secondary electron emission, and Bohm diffusion. It is shown that in order to explain the observed discharge current, the electron anomalous collision frequency νB has to be on the order of the Bohm value, νB≈ωc/16. The contribution of electron-wall collisions to cross-field transport is found to be insignificant.Conventional annular Hall Thrusters become inefficient when scaled to low power. Cylindrical Hall Thrusters, which have lower surface-to-volume ratio, are therefore more promising for scaling down. They presently exhibit performance comparable with conventional annular Hall Thrusters. Electron cross-field transport in a 2.6 cm miniaturized cylindrical Hall thruster (100 W power level) has been studied through the analysis of experimental data and Monte Carlo simulations of electron dynamics in the thruster channel. The numerical model takes into account elastic and inelastic electron collisions with atoms, electron-wall collisions, including secondary electron emission, and Bohm diffusion. It is shown that in order to explain the observed discharge current, the electron anomalous collision frequency νB has to be on the order of the Bohm value, νB≈ωc/16. The contribution of electron-wall collisions to cross-field transport is found to be insignificant.
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electron cross field transport in a low power cylindrical Hall thruster
Other Information: PBD: 24 Jun 2004, 2004Co-Authors: A. Smirnov, Yevgeny Raitses, Nathaniel J. FischAbstract:Conventional annular Hall Thrusters become inefficient when scaled to low power. Cylindrical Hall Thrusters, which have lower surface-to-volume ratio, are therefore more promising for scaling down. They presently exhibit performance comparable with conventional annular Hall Thrusters. Electron cross-field transport in a 2.6 cm miniaturized cylindrical Hall thruster (100 W power level) has been studied through the analysis of experimental data and Monte Carlo simulations of electron dynamics in the thruster channel. The numerical model takes into account elastic and inelastic electron collisions with atoms, electron-wall collisions, including secondary electron emission, and Bohm diffusion. We show that in order to explain the observed discharge current, the electron anomalous collision frequency {nu}{sub B} has to be on the order of the Bohm value, {nu}{sub B} {approx} {omega}{sub c}/16. The contribution of electron-wall collisions to cross-field transport is found to be insignificant.
Andrei A. Litvak - One of the best experts on this subject based on the ideXlab platform.
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experimental studies of high frequency azimuthal waves in Hall Thrusters
Physics of Plasmas, 2004Co-Authors: Andrei A. Litvak, Yevgeny Raitses, Nathaniel J. FischAbstract:High-frequency oscillations (1–100 MHz) are drawing significant attention in the recent research of Hall Thrusters. A diagnostic setup, consisting of single Langmuir probe, special shielded probe connector-positioner, and electronic impedance-matching circuit, was successfully built and calibrated. Through simultaneous high-frequency probing of the Hall-thruster plasma at multiple locations, high-frequency plasma waves have been successfully identified and characterized.
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Rayleigh instability in Hall Thrusters
Physics of Plasmas, 2004Co-Authors: Andrei A. Litvak, Nathaniel J. FischAbstract:Gradient-driven Rayleigh-type instabilities in Hall plasma Thrusters are analyzed using linearized two-fluid hydrodynamic equations. Necessary instability conditions and a general criterion for stability of azimutHally propagating perturbations are derived. For a simplified model of the axial distribution of parameters inside the thruster channel, the growth rate of an unstable wave, resonant with the azimuthal electron flow, is obtained. The frequency and phase relations are related to the results of experimental investigations of high-frequency oscillations in Hall Thrusters.
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Experimental Studies of Rayleigh Instability in Hall Thrusters
2003Co-Authors: Andrei A. Litvak, Yevgeny Raitses, Nathaniel J. FischAbstract:High-frequency oscillations (1-100MHz) are drawing significant attention in the recent research of Hall Thrusters. A diagnostic setup, consisting of single Langmuir probe, special shielded probe connector-positioner, and electronic impedance-matching circuit, was successfully built and calibrated. Through simultaneous high frequency probing of the Hall-thruster plasma at multiple locations, high-frequency plasma waves have been successfully identified and characterized. Submitted to Phys. Plasmas in 2003
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rayleigh instability in Hall Thrusters
38th AIAA ASME SAE ASEE Joint Propulsion Conference and Exhibit 2002, 2002Co-Authors: Andrei A. Litvak, Nathaniel J. FischAbstract:The importance of plasma oscillations for the successful operation of Hall current plasma Thrusters has been long recognized ~see, e.g., Ref. 1!. These oscillations play an important role in controlling the transport, conduction, and mobility in these devices, thus directly affecting their performance. These oscillations are also important in matching the thruster to the power processing circuit. The presence of plasma density and magnetic field gradients is one of the main sources for plasma instabilities. 2,3 However, despite general agreement with the early experimental data, 4 these models do not explain all of the observations, such as, for example, the presence of high-frequency ~MHz range! plasma oscillations, which were recently detected and characterized. 5,6 In this paper we study two-dimensional plasma perturbations in a Hall current plasma thruster on the basis of twofluid hydrodynamic theory. We focus on modes with purely azimuthal propagation, suggested by the experimental findings. 5 These findings include plasma oscillations in the presence of sharp gradients of plasma parameters, typical for operating regimes of state-of-the art Hall Thrusters. 7 We also include collisional terms for electrons. We show that Rayleigh-type instability of azimuthal electrostatic waves appears. We determine the instability frequency and growth rate for a particular model of steady-state axial distribution of parameters inside the thruster channel.
