The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
N. J. Fisch - One of the best experts on this subject based on the ideXlab platform.
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fast camera imaging of hall Thruster ignition
IEEE Transactions on Plasma Science, 2011Co-Authors: C L Ellison, Y Raitses, N. J. FischAbstract:Hall Thrusters provide efficient space propulsion by electrostatic acceleration of ions. Rotating electron clouds in the Thruster overcome the space charge limitations of other methods. Images of the Thruster start-up, taken with a fast camera, reveal a bright ionization period which settles into steady-state operation over 50 μs. The cathode introduces azimuthal asymmetry, which persists for about 30 μs into the ignition.
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Plasma Plume of Annular and Cylindrical Hall Thrusters
IEEE Transactions on Plasma Science, 2008Co-Authors: N. J. Fisch, Y. 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: Y. Raitses, Artem Smirnov, Erik Granstedt, N. 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: Y. Raitses, A Smirnov, N. 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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Cylindrical Hall Thrusters
37th AIAA Plasmadynamics and Lasers Conference, 2006Co-Authors: Y. Raitses, Artem Smirnov, N. J. FischAbstract:The cylindrical Hall Thruster, proposed and studied at the PPPL 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 Hall Thrusters. These characteristics were demonstrated in low and medium power ranges. For a miniaturized 100 W cylindrical Thruster, we achieved performance improvements, including a 30-40% plume narrowing, reliable discharge initiation, and stable operation in the discharge voltage range of 50-600 V. -
Y. Raitses - One of the best experts on this subject based on the ideXlab platform.
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Performance of Oscillating Plasma Thrusters
arXiv: Plasma Physics, 2020Co-Authors: Jacob Simmonds, Y. RaitsesAbstract:Traditional expressions and definitions describing performance of plasma Thrusters, including the thrust, specific impulse, and the Thruster efficiency, assume a steady state plasma flow with a constant flow velocity. However, it is very common for these Thrusters that the plasma exhibits unstable behavior resulting in time-variations of the thrust and the exhaust velocity. For example, in Hall Thrusters, the ionization instability leads to strong oscillations of the discharge current (so-called breathing oscillations), plasma density, ion energy, and as a result the ion flow. In this paper, we revisit the formulation of the thrust and the thrust efficiency to account for time variations of the ion parameters including the phase shift between the ion energy and the ion flow. For sinusoidal oscillations it was found thrust can potentially change more than 20%. It is shown that by modulating ion energy at specific amplitudes, thrust can be maximized in such regimes. Finally, an expression for the Thruster efficiency of the modulating Thruster is derived to show a mechanism for inefficiencies in such Thrusters.
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Plasma Plume of Annular and Cylindrical Hall Thrusters
IEEE Transactions on Plasma Science, 2008Co-Authors: N. J. Fisch, Y. 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: Y. Raitses, Artem Smirnov, Erik Granstedt, N. 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: Y. Raitses, A Smirnov, N. 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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Cylindrical Hall Thrusters
37th AIAA Plasmadynamics and Lasers Conference, 2006Co-Authors: Y. Raitses, Artem Smirnov, N. J. FischAbstract:The cylindrical Hall Thruster, proposed and studied at the PPPL 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 Hall Thrusters. These characteristics were demonstrated in low and medium power ranges. For a miniaturized 100 W cylindrical Thruster, we achieved performance improvements, including a 30-40% plume narrowing, reliable discharge initiation, and stable operation in the discharge voltage range of 50-600 V. -
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: Y. Raitses, A Smirnov, N. 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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electron cross field transport in a low power cylindrical hall Thruster
Physics of Plasmas, 2004Co-Authors: A Smirnov, Y. Raitses, N. 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, Y. Raitses, N. 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.
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plasma measurements in a 100 w cylindrical hall Thruster
Journal of Applied Physics, 2004Co-Authors: A Smirnov, Y. Raitses, N. J. FischAbstract:Conventional annular Hall Thrusters become inefficient when scaled to low power. Their lifetime decreases significantly due to the channel wall erosion. Cylindrical Hall Thrusters, which have lower surface-to-volume ratio and, thus, seem to be more promising for scaling down, exhibit performance comparable with conventional annular Hall Thrusters of the similar size. Plasma potential, ion density, and electron temperature profiles were measured inside the 2.6 cm cylindrical Hall Thruster with the use of stationary and slow movable emissive and biased Langmuir probes. Potential drop in the 2.6 cm cylindrical Hall Thruster is localized mainly in the cylindrical part of the channel and in the plume, which suggests that the Thruster should suffer lower erosion of the channel walls due to fast ion bombardment. Plasma density has a maximum of about (2.6–3.8)×1012 cm−3 at the Thruster axis. At the discharge voltage of 300 V, the maximum electron temperature is about 21 eV, which is not enough to produce multiple...
Richard R. Hofer - One of the best experts on this subject based on the ideXlab platform.
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Conducting Wall Hall Thrusters
IEEE Transactions on Plasma Science, 2020Co-Authors: Dan M. Goebel, Ira Katz, Richard R. Hofer, Ioannis G. Mikellides, James E. Polk, Brandon N. DotsonAbstract:A unique configuration of the magnetic field and channel geometry near the wall of Hall Thrusters, called magnetic shielding, has recently demonstrated the ability to significantly reduce the erosion of the boron nitride (BN) walls and extend the life of Hall Thrusters by orders of magnitude. The ability of magnetic shielding to minimize interactions between the plasma and the discharge chamber walls in regions where erosion typically occurs has for the first time enabled the replacement of insulating walls with conducting materials without loss in Hall Thruster performance. It is important to note that this is not a Thruster with anode layer (TAL) where the walls are at or near cathode potential, but is a Hall Thruster configuration where the walls are near the anode potential. The BN rings in the 6-kW H6 Hall Thruster were replaced with graphite that self-biased to near the anode potential during operation. The Thruster efficiency remained over 60% (within 2% of the baseline BN configuration) with a small decrease in thrust and increase in Isp typical of magnetically shielded Hall Thrusters. The graphite wall temperatures decreased significantly compared with both shielded and unshielded BN configurations, leading to the potential for higher power operation. Eliminating ceramic walls makes it simpler and less expensive to fabricate a Thruster to survive launch loads, and the graphite discharge chamber radiates more efficiently, which increases the power capability of the Thruster compared with conventional Hall Thruster designs.
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development and initial testing of a magnetically shielded miniature hall Thruster
IEEE Transactions on Plasma Science, 2015Co-Authors: Ryan W Conversano, Richard R. Hofer, Dan M. Goebel, Taylor S Matlock, Richard E. WirzAbstract:The scaling of magnetically shielded Hall Thrusters to low power is investigated through the development and fabrication of a 4-cm Hall Thruster. During initial testing, the magnetically shielded miniature Hall Thruster was operated at 275 V discharge voltage and 325-W discharge power. Inspection of the channel walls after testing suggests that the outer discharge channel wall was successfully shielded from high-energy ion erosion while the inner channel wall showed evidence of weaker shielding, likely due to magnetic circuit saturation. Scanning planar probe measurements taken at two locations downstream of the Thruster face provided ion current density profiles. The ion current calculated by integrating these data was 1.04 A with a plume divergence half-angle of 30°. Swept retarding potential analyzer measurements taken 80-cm axially downstream of the Thruster measured the most probable ion voltage to be 252 V. The total Thruster efficiency was calculated from probe measurements to be 43% (anode efficiency of 59%) corresponding to a thrust of 19 mN at a specific impulse of 1870 s. Discharge channel erosion rates were found to be approximately three orders of magnitude less than unshielded Hall Thrusters, suggesting the potential for a significant increase in operational life.
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mass and cost model for selecting Thruster size in electric propulsion systems
Journal of Propulsion and Power, 2013Co-Authors: Richard R. Hofer, Thomas RandolphAbstract:A model of system mass and life-cycle costs is used to determine the optimal number of Thrusters for electric propulsion systems. The model is generalized for application with most electric propulsion systems and then applied to high-power Hall Thruster systems in particular. Mass and cost models were constructed for individual Thruster strings using as inputs the number of active Thrusters, the number of redundant Thrusters, and the total system power. Mass and cost are related through the launch cost of the propulsion-system mass, which unifies the optimization to a single global parameter based on cost. Fault-tolerance and string cost are driving factors determining the optimum Thruster size for a given system-power level. After considering factors such as fault-tolerance, cost uncertainty, complexity, ground-test-vacuum-facility limitations, previously demonstrated power capabilities, and possible technology limitations, the development of two Thrusters to flight status is suggested: a low-power model...
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Mass and Cost Model for Selecting Thruster Size in Electric Propulsion Systems
Journal of Propulsion and Power, 2013Co-Authors: Richard R. Hofer, Thomas M. RandolphAbstract:A model of system mass and life-cycle costs is used to determine the optimal number of Thrusters for electric propulsion systems. The model is generalized for application with most electric propulsion systems and then applied to high-power Hall Thruster systems in particular. Mass and cost models were constructed for individual Thruster strings using as inputs the number of active Thrusters, the number of redundant Thrusters, and the total system power. Mass and cost are related through the launch cost of the propulsion-system mass, which unifies the optimization to a single global parameter based on cost. Fault-tolerance and string cost are driving factors determining the optimum Thruster size for a given system-power level. After considering factors such as fault-tolerance, cost uncertainty, complexity, ground-test-vacuum-facility limitations, previously demonstrated power capabilities, and possible technology limitations, the development of two Thrusters to flight status is suggested: a low-power model operating at 20-50 kW per Thruster to support missions up to 500 kW system power and the development of a high-power model operating at 50-100 kW per Thruster to support missions up to 1 MW system power.
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design of a laboratory hall Thruster with magnetically shielded channel walls phase ii experiments
48th AIAA ASME SAE ASEE Joint Propulsion Conference & Exhibit, 2012Co-Authors: Richard R. Hofer, Dan M. Goebel, Ioannis G. Mikellides, Ira KatzAbstract:Magnetic shielding in Hall Thrusters significantly reduces the transport of high-energy ions to the channel walls such that erosion is effectively eliminated. The physics of magnetic shielding were validated through laboratory experiments demonstrating essentially erosionless, high-performance Hall Thruster operation for the first time. The magnetic field near the walls of a high-performance Hall Thruster was modified to enable magnetic shielding while maintaining the magnetic field topology away from the walls necessary to retain efficient operation. Sixteen diagnostics were deployed to assess the performance, thermal, stability, and wear characteristics of the Thruster in its original and modified configurations. At 300 V, 6 kW the total efficiency decreased from 63.5% to 62.4% while specific impulse increased from 1950 s to 2000 s. Wall temperatures in the last 30% of the channel were reduced by 12-16%. The amplitude of discharge current oscillations increased 25% with otherwise no noticeable change in the stability of the discharge. Plasma measurements at the walls validate our understanding of magnetic shielding as derived from the theory. The plasma potential was maintained very near the anode potential, the electron temperature was reduced by a factor of two to three, and the ion current density was reduced by at least a factor of two. Measurements of the carbon backsputter rate, wall geometry, and direct measurement of plasma properties at the wall indicate the wall erosion rate was reduced by 1000X relative to the unshielded Thruster and by 100X relative to unshielded Hall Thrusters late in life. These changes effectively eliminate wall erosion as a life limitation or failure mode in Hall Thrusters and make them, for all intents and purposes, immortal.
R. Hallmann - One of the best experts on this subject based on the ideXlab platform.
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Thruster interaction effects on a dp shuttle tanker wake flow measurements of the main propeller and bow tunnel Thrusters
ASME 2014 33rd International Conference on Ocean Offshore and Arctic Engineering, 2014Co-Authors: J. L. Cozijn, R. HallmannAbstract:This paper discusses Thruster interaction effects for a DP shuttle tanker, equipped with two main propellers and rudders, as well as two bow tunnel Thrusters. Thruster-interaction model tests were carried out in MARIN’s Deepwater Towing Tank. Detailed PIV measurements were taken of the wake flow behind the main propellers and rudders. Furthermore, PIV measurements were taken of the wake flow of one of the two bow tunnel Thrusters. The flow velocities were measured in a large number of cross sections at different down-stream positions. The PIV measurements provide a detailed image of the velocities in the Thruster wake, showing axial velocities, as well as transverse and vertical velocity components.The results of the first set of measurements showed in detail the wake flow behind the main propeller of the DP shuttle tanker. The wake flow pattern was determined at rudder angles of 0 deg and 10 deg. Since the research is related to DP performance, bollard pull conditions (zero forward speed) were considered in the model tests.The results of the second set of measurements showed in detail the wake flow of one of the bow tunnel Thrusters. The wake flow pattern was investigated in zero speed conditions, as well as for the vessel at forward speed. The observed flow patterns helped to explain the reduced bow tunnel performance at forward speed.The results of the present research are used to further improve the understanding of the physics of Thruster interaction effects. Furthermore, the results will serve as validation material for CFD calculations that are currently being performed.© 2014 ASME
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Thruster-Interaction Effects on a DP Semi-Submersible and a Drill Ship: Measurement and Analysis of the Thruster Wake Flow
Volume 1: Offshore Technology, 2013Co-Authors: J. L. Cozijn, R. HallmannAbstract:Thruster-interaction model tests were carried out in MARIN’s Deepwater Towing Tank. Detailed PIV measurements were performed of the wake flow behind the azimuthing Thrusters on two different DP vessels, a Semi-submersible and a Drill Ship. The flow velocities were measured in a large number of cross sections at different distances from the Thrusters. The PIV measurements provide a detailed image of the flow velocities in the Thruster wake, showing the axial velocities, as well as the transverse and vertical velocity components.First, measurements were carried out on a DP Semi-submersible (scale 1:40), which was equipped with 8 azimuthing Thrusters. The results of the PIV measurements show the wake flow, interacting with nearby Thrusters and the opposite pontoon of the semi-submersible. An example is shown in Figure 1 below. Deflection of the Thruster wake, caused by the Coanda effect, was observed. The results for Thrusters with a 7 deg downward tilt were compared with the results for Thrusters with a horizontal propeller axis. Furthermore, the effect of ambient current was investigated.Second, measurements were carried out on a DP Drill Ship (scale 1:40), which had 6 azimuthing Thrusters. The results of these PIV measurements also gave insight in the wake flow behind the azimuthing Thrusters and the interactions between neighbouring Thrusters. An example is shown in Figure 2 below. In this case, special attention was paid to the development of the Thruster wake along the vessel length, up to a distance of more than 40D downstream.The results of the present research are used to further improve the understanding of the physics of Thruster interaction effects. Furthermore, the results will serve as validation material for CFD calculations that are foreseen in the near future.Copyright © 2013 by ASME
