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.

Download or read book Ion Velocity Measurements in a Linear Hall Thruster written by and published by . This book was released on 2005 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents the general operation and the near exit plane velocity field of the Stanford Linear Hall thruster in a high vacuum environment. The ionized propellant velocities were measured using laser induced fluorescence of the excited state xenon ionic transition at 834.7 nm. Ion velocities were interrogated from the channel exit plane to a distance 30 mm from it. Both axial and transverse (along the electron Hall current direction) velocities were measured. These results presented here, combined with those of previous works, highlight the high sensitivity of electron mobility inside and outside the channel, depending on the background gas density, type of wall material, or magnetic field intensity. When operated with a low background pressure, the particular Hall discharge studied here creates an ion accelerating electrostatic field mainly outside of the channel, in a narrow zone located 5-20 mm away from the exit plane.

Download or read book Background Pressure Effects on Internal and Near field Ion Velocity Distribution of the BHT 600 Hall Thruster Preprint written by and published by . This book was released on 2008 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presented is a study of the effects of chamber background pressure on the ion axial velocity distribution within the discharge chamber and in the near-field of the Busek BHT-HD-600 xenon Hall effect thruster. Ion velocity distributions were measured along the acceleration channel centerline using laser-induced fluorescence of the 5d[4](sub 7/2)-6p[3](sub 5/2) xenon ion excited state transition. Measurements were taken at the lowest possible chamber background pressure and a pressure that was a factor of two higher. In addition to varying the background pressure, the magnetic field of the discharge chamber was switched between two configurations. The radial magnetic was set to a low and high strength case, which produced two different anode current oscillatory regimes. Ion axial velocity distribution function peaks were used to approximate ion energy and axial electric field strength to compare the acceleration profiles of the tested thruster operating conditions. Increasing background pressure shifted the ion acceleration region upstream in the discharge chamber. The width of the velocity distributions correlated strongly to the radial magnetic field strength. The high magnetic field case data showed narrower peaks.

Download or read book Hall Thruster With an External Acceleration Zone written by and published by . This book was released on 2005 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents the general operation and the near exit plane ion velocity field of the Stanford Linear Hall Thruster in a high vacuum environment. The ionized propellant velocities were measured using laser induced fluorescence of the excited state xenon ionic transition at 834.7 nm. Ion velocities were interrogated from the channel exit plane to a distance 30 mm from it. Both axial and cross-field (along the electron Hall current direction) velocities were measured. The results presented here, combined with those of previous work, highlight the high sensitivity of electron mobility inside and outside the channel, depending on the background gas density, type of wall material, or magnetic field intensity. When operated with a low background pressure, the particular Hall discharge studied here creates an ion accelerating electrostatic field mainly outside of the channel, in a narrow zone located 5-20 mm away from the exit plane.

Download or read book Evolution of the Ion Velocity Distribution in the Near Field of a 200 W Hall Thruster Preprint written by and published by . This book was released on 2006 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents an analysis of near plume velocity distributions of the Busek BHT-200-X3 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. The evolution of the axial and radial velocity distributions is presented from the exit plane to approximately 0.7 exit diameters downstream. It is shown that the distributions evolve significantly between the exit channel center and the inner portion of the channel where there are high frac-tions of low velocity ions. It is believed that this may be due to the slight inward focus of the xenon ion propellant colliding on the surface, recombining, and subsequently being re-ionized. Low axial velocity ions appear downstream of the thruster exit plane. While their origin is not entirely certain, the most likely explanation appears to be cross annular flow. Strong evidence of charge exchange is also evident producing high velocity wings on the primary ion velocity peak reminiscent of ion energy analyzer studies of other thrusters. A survey of the axial and radial velocity distributions along the exposed exterior boron nitride nose cone covering the central magnetic pole is performed to determine the behavior of the ions impacting this critical surface. The VDF is ideal for comparison with numerical simulations since it allows for direct comparison of the fundamental ion acceleration. External VDF data can even provide limited insight as to the internal ion formation and acceleration processes.

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.

Download or read book Comparison of Numerical and Experimental Near Field Ion Velocity Distributions of the BHT 200 X3 Hall Thruster written by and published by . This book was released on 2006 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: Near-field ion velocity distributions of a BusekBHT-200-X3 xenon Hall thruster obtained through numerical simulation are compared with laser-induced fluorescence measurements taken for one nominal operating condition. The numerical code Hybrid-PIC Hall, a 2D hybrid particle-in-cell model, is used to simulate an axisymmetric cross section of the plasma acceleration zone. A set of nine HP Hall simulations are run using three different cathode positions and Bohm electron mobility coefficients to study the effects of these parameters on ion acceleration. Six additional cases were run in an attempt to better match the simulation results to the experimental data. For model validation, agreement between the numerical and experimental results is examined. The results show that it is difficult to match both the global operational parameters (i.e, thrust, discharge current, and beam current) and the ion velocity distributions. The shape of the axial velocity distributions can be closely matched by using high Bohm electron mobility values. However, this correlation comes at the expense of peak ion velocity and discharge current agreement. Radial velocity distributions are more closely matched by the simulations, but the simulations uniformly predict lower than measured inward and higher than measured outward radial velocity components (relative to the centerline) from the annular acceleration channel.

Download or read book Evolution of the Ion Velocity Distribution in the Near Field of the BHT 200 X3 Hall Thruster written by and published by . This book was released on 2006 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents an analysis of near plume velocity distributions of the Busek BHT-200-X3 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. The evolution of the axial and radial velocity distributions is presented from the exit plane to approximately 0.7 exit diameters downstream. It is shown that the distributions evolve significantly between the exit channel center and the inner portion of the channel where there are high frac-tions of low velocity ions. It is believed that this may be due to the slight inward focus of the xenon ion propellant colliding on the surface, recombining, and subsequently being re-ionized. Low axial velocity ions appear downstream of the thruster exit plane. While their origin is not entirely certain, the most likely explanation appears to be cross annular flow. Strong evidence of charge exchange is also evident producing high velocity wings on the primary ion velocity peak reminiscent of ion energy analyzer studies of other thrusters. A survey of the axial and radial velocity distributions along the exposed exterior boron nitride nose cone covering the central magnetic pole is performed to determine the behavior of the ions impacting this critical surface. The VDF is ideal for comparison with numerical simulations since it allows for direct comparison of the fundamental ion acceleration. External VDF data can even provide limited insight as to the internal ion formation and acceleration processes.

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.

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:

Download or read book Near Plume Laser Induced Fluorescence Velocity Measurements of a 600 W Hall Thruster Preprint written by and published by . This book was released on 2008 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents the near exit plane velocity field of the Busek Company BHT-600-Circular 600 W Hall thruster at a single operating condition with a 300 V anode potential. The xenon ion propellant velocities were measured using laser induced fluorescence of the 5d[4]7/2 - 6p[3] 5/2 excited state xenon ionic transition at 834.72 nm. Ion velocities were interrogated from the acceleration channel exit plane to a distance 100 mm from the exit plane (1.6 exit plane diameters). Both axial and radial velocities were directly measured. A nearly uniform axial velocity profile of approximately 17,000 m/s (197 eV) was measured at the acceleration channel center on the exit plane. The maximum axial velocity was measured 100 mm from the exit plane at 19,800 m/s (267 eV). Radial velocity measurements were used to determine the divergence of the plume, as well as in conjunction with the coaxial symmetry of the thruster to determine azimuthal velocities in several regions proximate to the exit plane. The 475 m/s mean azimuthal velocity was measured 5 mm from the exit plane. From this value, it is possible to estimate a maximum thruster induced torque of 3.2 x 10(exp.-5) Nm. Due to the divergence and convergence of the coaxial ion flow, distinct ion populations were observed to interact in the central core of the near plume. This is apparent in measurement volumes where multiple radial and axial velocity components were measured. These regions also typically correspond with the brightest portions of the visible plume.

Download or read book Effect of Anode Current Fluctuations on Ion Energy Distributions Within a 600 W Hall Effect Thruster Preprint written by and published by . This book was released on 2008 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents axial ion energy distribution measurements within the acceleration channel of the 600 W Busek Co. Inc. BHT-HD-600 laboratory Hall thruster derived from laser-induced fluorescence measurements of the 5d[4](sub 7/2) - 6p[3](sub 5/2) xenon ion excited state transition. Acceleration channel centerline ion energy distributions are measured for three closely related operating conditions which only differ in the magnitude of the radial magnetic field strength. These three operating conditions span a broad range of discharge current oscillations strength. The 0 to 200 kHz frequency domain is characterized, and the dominant 40 kHz to 50 kHz frequency appears most likely to be axially traveling ionization waves, commonly known as the breathing mode oscillations. These oscillations manifest themselves to the laser induced fluorescence diagnostic as clearly broadened ion energy distributions when the oscillation strength is high. We determine the spatial extent of the axial breathing mode oscillation nonintrusively. The coherence and magnitude of the discharge current oscillations are inversely proportional to acceleration channel radial magnetic strength.

Download or read book Scaling Laws and Electron Properties in Hall Effect Thrusters written by Käthe Dannenmayer and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: All satellites need a propulsion system for orbit correction maneuvers. Electric Hall effect thrusters are an interesting technology for space applications. The big advantage compared to chemical propulsion devices is the higher specific impulse Isp, a higher ejection speed and thus a substantial gain in terms of propellant consumption. In a Hall effect thruster the ions are created and accelerated in a low pressure discharge plasma in a magnetic field. The first part of the work concerns scaling laws for Hall effect thrusters. A semi-empirical scaling model based on analytical laws and relying on simplifying assumptions is developed. This scaling model can be used to extrapolate existing thruster technologies in order to meet new mission requirements. In a second part, the influence of the channel width on the thruster performance level is investigated. It has been demonstrated that enlarging the channel width of a low power Hall effect thruster leads to an increase in thruster efficiency. Finally, electron properties are measured by means of electrostatic probes in the plume of different Hall effect thrusters. Experimental data on electron properties is of great interest for the validation of numerical plume models that are essential for the integration of the thruster on the satellite. Time-averaged and timeresolved measurements of the electron properties have been carried out for different operating conditions of the thruster. A fast-moving probe system has been developed in order to perform measurements of the electron properties close to the thruster exit plane.

Download or read book Recent Results from Internal and Very Near Field Plasma Diagnostics of a High Specific Impulse Hall Thruster written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-20 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: Floating potential and ion current density measurements were taken on the laboratory model NASA-173Mv2 in order to improve understanding of the physical processes affecting Hall thruster performance at high specific impulse. Floating potential was measured on discharge chamber centerline over axial positions spanning 10 mm from the anode to 100 mm downstream of the exit plane. Ion current density was mapped radially up to 300 mm from thruster centerline over axial positions in the very-near-field (10 to 250 mm from the exit plane). All data were collected using a planar probe in conjunction with a high-speed translation stage to minimize probe-induced thruster perturbations. Measurements of floating potential at a xenon flow rate of 10 mg/s have shown that the acceleration layer moved upstream 3 1 mm when the voltage increased from 300 to 600 V. The length of the acceleration layer was 14 2 mm and was approximately constant with voltage and magnetic field. Ion current density measurements indicated the annular ion beam crossed the thruster centerline 163 mm downstream of the exit plane. Radial integration of the ion current density at the cathode plane provided an estimate of the ion current fraction. At 500 V and 5 mg/s, the ion current fraction was calculated as 0.77. Hofer, Richard R. and Gallimore, Alec D. and Jacobson, David (Technical Monitor) Glenn Research Center NASA/CR-2003-212604, E-14162, IEPC-2003-037

Download or read book Ion Voltage Diagnostics in the Far Field Plume of a High Specific Impulse Hall Thruster written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-08-20 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effects of the magnetic field and discharge voltage on the far-field plume of the NASA 173Mv2 laboratory-model Hall thruster were investigated. A cylindrical Langmuir probe was used to measure the plasma potential and a retarding potential analyzer was employed to measure the ion voltage distribution. The plasma potential was affected by relatively small changes in the external magnetic field, which suggested a means to control the plasma surrounding the thruster. As the discharge voltage increased, the ion voltage distribution showed that the acceleration efficiency increased and the dispersion efficiency decreased. This implied that the ionization zone was growing axially and moving closer to the anode, which could have affected thruster efficiency and lifetime due to higher wall losses. However, wall losses may have been reduced by improved focusing efficiency since the total efficiency increased and the plume divergence decreased with discharge voltage. Hofer, Richard R. and Haas, James M. and Gallimore, Alec D. Glenn Research Center NASA/CR-2003-212895, AIAA Paper 2003-4556, E-14313

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.

Download or read book Plume and Discharge Plasma Measurements of an Nstar Type Ion Thruster written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2018-09-27 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt: The success of the NASA Deep Space I spacecraft has demonstrated that ion propulsion is a viable option for deep space science missions. More aggressive missions such as Comet Nuclear Sample Return and Europa lander will require higher power, higher propellant throughput and longer thruster lifetime than the NASA Solar Electric Propulsion Technology Application Readiness (NSTAR) engine. Presented here are thruster plume and discharge plasma measurements of an NSTAR-type thruster operated from 0.5 kW to 5 kW. From Faraday plume sweeps, beam divergence was determined. From Langmuir probe plume measurements on centerline, low energy ion production on axis due to charge-exchange and direct ionization was assessed. Additionally, plume plasma potential measurements made on axis were used to determine the upper energy limits at which ions created on centerline could be radially accelerated. Wall probes flush-mounted to the thruster discharge chamber anode were used to assess plasma conditions. Langmuir probe measurements at the wall indicated significant differences in the electron temperature in the cylindrical and conical sections of the discharge chamber. Foster, John E and Soulas, George C. and Patterson, Michael J. Glenn Research Center NASA/TM-2000-210382, E-12438, AIAA Paper 2000-3812, NAS 1.15:210382