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Electron Transport And Ion Acceleration In A Low Power Cylindrical Hall Thruster
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Book Synopsis Electron Transport and Ion Acceleration in a Low-power Cylindrical Hall Thruster by :
Download or read book Electron Transport and Ion Acceleration in a Low-power Cylindrical Hall Thruster written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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. The plasma density peak observed at the axis of the 2.6 cm cylindrical Hall thruster is likely to be due to the convergent flux of ions, which are born in the annular part of the channel and accelerated towards the thruster axis.
Book Synopsis Electron Transport and Ion Acceleration in a Low-power Cylindrical Hall Thruster by : A. I. Smirnov
Download or read book Electron Transport and Ion Acceleration in a Low-power Cylindrical Hall Thruster written by A. I. Smirnov and published by . This book was released on 2004 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Electron Cross-field Transport in a Low Power Cylindrical Hall Thruster by : A. I. Smirnov
Download or read book Electron Cross-field Transport in a Low Power Cylindrical Hall Thruster written by A. I. Smirnov and published by . This book was released on 2004 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Fundamentals of Electric Propulsion by : Dan M. Goebel
Download or read book Fundamentals of Electric Propulsion written by Dan M. Goebel and published by John Wiley & Sons. This book was released on 2008-12-22 with total page 528 pages. Available in PDF, EPUB and Kindle. Book excerpt: Throughout most of the twentieth century, electric propulsion was considered the technology of the future. Now, the future has arrived. This important new book explains the fundamentals of electric propulsion for spacecraft and describes in detail the physics and characteristics of the two major electric thrusters in use today, ion and Hall thrusters. The authors provide an introduction to plasma physics in order to allow readers to understand the models and derivations used in determining electric thruster performance. They then go on to present detailed explanations of: Thruster principles Ion thruster plasma generators and accelerator grids Hollow cathodes Hall thrusters Ion and Hall thruster plumes Flight ion and Hall thrusters Based largely on research and development performed at the Jet Propulsion Laboratory (JPL) and complemented with scores of tables, figures, homework problems, and references, Fundamentals of Electric Propulsion: Ion and Hall Thrusters is an indispensable textbook for advanced undergraduate and graduate students who are preparing to enter the aerospace industry. It also serves as an equally valuable resource for professional engineers already at work in the field.
Book Synopsis Ion Velocity Measurements Within the Acceleration Channel of a Low Power Hall Thruster (preprint) by : William A. Hargus (Jr)
Download or read book Ion Velocity Measurements Within the Acceleration Channel of a Low Power Hall Thruster (preprint) written by William A. Hargus (Jr) and published by . This book was released on 2007 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: "This work presents axial ion velocity measurements within the acceleration channel of the Busek Co. Inc. BHT-200 200 W laboratory Hall thruster derived from laser-induced fluorescence measurements of the 5d[4]7/2-6p[3]5/2 xenon ion excited state transition. Acceleration channel centerline ion velocities were measured for one nominal and six related cases. These six cases were chosen to be representative of small variations of the applied propellant flow, magnetic field, and discharge charge potential from the nominal condition. These deviations in operating parameters translate into changes in the plasma density, electron transport, and applied electric field, respectively. The effect of varying the magnetic field, hence influencing the electron transport, is to adjust the location of the internal ion acceleration. Increasing the anode propellant flow, which proportionally increases the plasma density and also influences the electron transport, appears to shift the acceleration upstream. Increasing discharge potential increases ion acceleration proportionally. Preliminary examination of the fluorescence traces, which have been previously shown to be representative of the ion velocity distributions, are also undertaken."--P. 1.
Book Synopsis Electron Cross-field Transport in a Low Power Cylindrical Hall Thruster by :
Download or read book Electron Cross-field Transport in a Low Power Cylindrical Hall Thruster written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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} ≈ [omega]{sub c}/16. The contribution of electron-wall collisions to cross-field transport is found to be insignificant.
Book Synopsis Transition in Electron Transport in a Cylindrical Hall Thruster by :
Download or read book Transition in Electron Transport in a Cylindrical Hall Thruster written by and published by . This book was released on 2010 with total page 191 pages. Available in PDF, EPUB and Kindle. Book excerpt: Through the use of high-speed camera and Langmuir probe measurements in a cylindrical Hall thruster, we report the discovery of a rotating spoke of increased plasma density and light emission which correlates with increased electron transport across the magnetic field. As cathode electron emission is increased, a sharp transition occurs where the spoke disappears and electron transport decreases. This suggests that a significant fraction of the electron current might be directed through the spoke.
Book Synopsis Electron Cross-field Transport in a Miniaturized Cylindrical Hall Thruster by : Raitses Yevgeny Smirnov Artem (Fisch Na)
Download or read book Electron Cross-field Transport in a Miniaturized Cylindrical Hall Thruster written by Raitses Yevgeny Smirnov Artem (Fisch Na) and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Conventional annular Hall thrusters become inefficient when scaled to low power. Cylindrical Hall thrusters, which have lower surface-to-volume ratio, are more promising for scaling down. They presently exhibit performance comparable with conventional annular Hall thrusters. The present paper gives a review of the experimental and numerical investigations of electron crossfield transport in the 2.6 cm miniaturized cylindrical Hall thruster (100 W power level). We show that, in order to explain the discharge current observed for the typical operating conditions, 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. The optimal regimes of thruster operation at low background pressure (below 10{sup -5} Torr) in the vacuum tank appear to be different from those at higher pressure ({approx} 10{sup -4} Torr).
Book Synopsis 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit July 11-14, 2004, Fort Lauderdale, FL.: 04-4100 - 04-4149 by :
Download or read book 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit July 11-14, 2004, Fort Lauderdale, FL.: 04-4100 - 04-4149 written by and published by . This book was released on 2004 with total page 574 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Ion and Electron Transport in an NSTAR-Derivative Ion Thruster by :
Download or read book Ion and Electron Transport in an NSTAR-Derivative Ion Thruster written by and published by . This book was released on 2001 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Field Structure and Electron Transport in the Near-field of Coaxial Hall Thrusters by : Andrew Wayne Smith
Download or read book Field Structure and Electron Transport in the Near-field of Coaxial Hall Thrusters written by Andrew Wayne Smith and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Hall thruster is an electric propulsion device developed in the former USSR during the Cold War, capable of efficiently providing sustained, low-levels of thrust. Coaxial Hall thrusters are comprised of an annular channel (at the base of which the anode is generally found), and a series of electromagnets that produce a predominantly radial magnetic field near the channel exit. A cathode, located outside the annular channel, injects electrons that serve a dual purpose: they neutralize the ion beam, and they sustain the core discharge. They plasma ions can achieve considerable exhaust velocities, lending the Hall thruster a high specific impulse; however, the propellant flow rate is generally on the order of a few mg/s, keeping the overall thrust low. Despite their desirable high efficiency, the detailed physics of Hall thruster operation is not clearly understood. In particular, the mechanism by which electrons are able to diffuse across the magnetic field lines at a rate in excess of classical predictions is the subject of dispute and ongoing research. Rectifying this deficiency within the near-field region (defined to lie between the exit plane of the annular channel and the external cathode) is the primary motivation for this work. A clear understanding of the mechanisms of electron transport in the near-field can aid the development of more efficient thrusters and provide direction for future experiments. The present study approaches the problem on two fronts. First, an extensive, 3-D map of the plasma potential (in addition to the floating potential and electron temperature) is obtained via a series of time-resolved experiments. These transient measurements are referenced to the periodic oscillation in the discharge current of Hall thrusters (known as the breathing-mode) and provide an unprecedented visualization of the low-frequency field dynamics. Second, the electron transport physics in the near-field is investigated in 3-D, electron-kinetic simulations. These simulations implement the experimentally-observed plasma potential (and, in some cases, fluctuations in the plasma potential). These simulations demonstrate that the 3-D nature of the fields is an important driver of near-field transport; however, collisions with the front-face of the thruster are critical to the anomalous diffusion of electrons across the magnetic field lines in this region. In simulations that considered static fields, up to 35 % of the electrons reached the channel during simulated lifetimes exceeding 1 microsecond, but often yielded very inhomogeneous density distributions. Imposing the measured helical plasma potential fluctuations in the simulations resulted in a dramatic azimuthal homogenization of the electron density distribution, and reduced the fraction of electrons reaching the channel to about 10 %, on par with experimental observations. In every case tested, plasma potential fluctuations (both axial and helical at a variety of frequencies) reduced the electron current reaching the channel. The results further suggest that the location and orientation of the cathode (as well as the properties of the emitted electron beam) have a strong effect on the transport. Gas-phase collisions, even when allowed to occur at a greatly exaggerated rate, are found to have negligible effect on either the channel/beam current ratio or the density distribution in the near-field. These results also suggest that random turbulence in the plasma properties (at least for frequencies less than or equal to 10 MHz) is unlikely to significantly impact the net electron transport (i.e., the channel/beam current ratio or density distribution). Importantly, axisymmetric simulations are found to yield dramatically disparate results (often yielding zero electron-current transport to the channel) compared to the simulations that considered 3-D fields (which introduce azimuthal components in the electric and magnetic fields); a result which questions the validity of pervasive 2-D Hall thruster simulations.
Book Synopsis Optimization of Cylindrical Hall Thrusters by :
Download or read book Optimization of Cylindrical Hall Thrusters written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Ion Collimation and In-channel Potential Shaping Using In-channel Electrodes for Hall Effect Thrusters by : Kunning Gabriel Xu
Download or read book Ion Collimation and In-channel Potential Shaping Using In-channel Electrodes for Hall Effect Thrusters written by Kunning Gabriel Xu and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This work focuses on improving the thrust-to-power ratio of Hall effect thrusters using in-channel electrodes to reduce ion-wall neutralization and focus the ion beam. A higher thrust-to-power ratio would give Hall thrusters increased thrust with the limited power available on spacecraft. A T-220HT Hall thruster is modified in this work to include a pair of ring electrodes within inside the discharge channel. The electrodes are biased above anode potential to repel ions from the walls and toward the channel centerline. Theoretical analysis of ion loss factors indicate that ion-wall neutralizations remove almost 13% of the total ions produced. Reduced wall losses could significantly improve the thruster performance without increased discharge power or propellant consumption. The thruster performance, plume ion characteristics, and internal plasma contours are experimentally measured. The plume and internal plasma measurements are important to determine the cause of the performance changes. The thruster is tested in three conditions: no electrode bias, low bias (10 V), and high bias (30 V). The performance measurements show the electrodes do indeed improve the thrust and thrust-to-power ratio, the latter only at the low bias level. Adding bias increases the ion density and decreases the plume angle compared to the no bias case. The plume measurements indicate that the performance improvements at low bias are due to increased ion number density as opposed to increased ion energy. The increased ion density is attributed to reduced wall losses, not increased ionization. The in-channel measurements support this due to little change in the acceleration potential or the electron temperature. At the high bias level, a drop in thrust-to-power ratio is seen, even though a larger increase in thrust is observed. This is due to increased power draw by the electrodes. Plume measurements reveal the increased thrust is due to ion acceleration. The internal measurements show increased acceleration potential and electron energy which can lead to increased ionization. At the high bias condition, the electrodes become the dominant positive terminal in the thruster circuit. This causes the increased ion acceleration and the creation of domed potential contours that conform to the near-wall cusp-magnetic fields. The domed contours produce focused electric fields, which cause the decreased wall losses and plume angle.
Book Synopsis Performance Evaluation of the SPT-140 by :
Download or read book Performance Evaluation of the SPT-140 written by and published by . This book was released on 1997 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Plasma Oscillations and Associated Electron Transport Within Hall Thrusters by : Aaron Kombai Knoll
Download or read book Plasma Oscillations and Associated Electron Transport Within Hall Thrusters written by Aaron Kombai Knoll and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Hall thruster is a type of plasma propulsion system for space vehicle applications. The thrust produced by this device is derived from the momentum of ions, which are accelerated to high exit velocities by the action of an electric field sustained within the plasma. The advantage of the Hall thruster compared to conventional chemical rocket propulsion is a significantly higher exhaust velocity, which leads to better utilization of propellant mass. Since the early days of Hall thruster research, experiments have suggested that the mobility of electrons along the axis of the thruster, perpendicular to an imposed magnetic field, is higher than can be explained by classical collision transfer processes alone. A lack of understanding regarding the mechanism for this enhanced mobility has proved a significant challenge toward the development of reliable simulations capable of predicting the performance of these devices. This thesis examines the role of high frequency plasma oscillations on the electron mobility using a combination of experimental studies on a laboratory Hall thruster, and numerical simulations capable of capturing these oscillations and quantifying their impact on the electron mobility. Two high frequency oscillations were consistently observed in the experiments: a 10MHz mode which appeared strongest in the vicinity of the anode, and a 4.5MHz mode which was strongest in the mid-channel region of the thruster. These were relatively low wave number (long wavelength) oscillations: approximately 6cm for the 4.5MHz oscillation and 3cm for the 10MHz oscillation. The angle of these waves varied considerably depending on the operating conditions of the thruster. They were found to be closely aligned to the axis of the thruster for experiments conducted with Xenon propellant, and were aligned with the circumference of the thruster (in the direction of electron drift) for experiments conducted with Krypton. A Hall thruster simulation, formulated in the axial-azimuthal coordinates of the thruster, was able to capture high frequency oscillations in reasonable agreement with experimental findings: 13MHz near the anode and 5MHz in the mid-channel region of the thruster for 160V discharge conditions. The simulation results demonstrated the crucial role of these oscillations in regulating the electron transport. In the vicinity of these oscillations the electron mobility was increased by a factor of five or more. The central finding of this thesis is that high frequency oscillations in the range 1 - 50MHz can account for the observed discrepancy between classical and experimental electron mobility in the Hall thruster.
Book Synopsis Investigation of Low Discharge Voltage Hall Thruster Operating Modes and Ionization Processes by :
Download or read book Investigation of Low Discharge Voltage Hall Thruster Operating Modes and Ionization Processes written by and published by . This book was released on 2009 with total page 45 pages. Available in PDF, EPUB and Kindle. Book excerpt: A study of low discharge voltage Hall thruster operation revealed the existence of two operating regimes. Small variations in cathode flow fraction and magnetic field resulted in sharp changes in discharge current with constant thrust, corresponding to a visible change in the jet-mode plume structure. The phenomenon is characterized with a systematic map of thruster operation for discharge voltages ranging from 100 - 120 V, anode flow rates from 10 - 20 mg/s, and cathode flow rates from 7% to 25% of the anode flow. Far-field plume measurements show electron current to the anode is decreased during this transition. The ion energy distributions exhibit significant differences between the high-current and low-current operating modes. These differences are indicative of a significant increase in the fraction of low-energy multiply charged ions and a longer region of primary ion acceleration in the high-current mode.
Book Synopsis Enhanced Performance of Cylindrical Hall Thrusters by :
Download or read book Enhanced Performance of Cylindrical Hall Thrusters written by and published by . This book was released on 2007 with total page 368 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
