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INVESTIGATION OF LOW DISCHARGE VOLTAGE HALL THRUSTER
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When nothing seems to help I go and look at a stonecutter hammering away at his rock. perhaps a hundred times without as much as a crack showing in it Yet at the hundred and first. blow it will split in two and I know it was not that blow that did it but all that had gone before. Jacob Riis 1849 1914 Danish American Photographer Journalist Social Reformer. Distribution A Approved for Public Release Distribution Unlimited. Daniel Lucas Brown 2009,All Rights Reserved,Acknowledgements. My path through undergraduate and graduate school has definitely been the road. less traveled I rarely envisioned what the next step would bring yet found new. opportunities guidance and support at each turn Each mentor along the way provided. unique experiences challenges and wisdom I ve been fortunate to have their leadership. and develop good friends along the way, First and foremost I d like to thank my advisor at Michigan Professor Alec. Gallimore Alec these last five years have been an honor While I ve spent a majority of. my time in the desert at AFRL you ve always been available when I needed direction. and granted the latitude when I needed room to grow i e learn from mistakes Alec. attracts students who are highly motivated and assert themselves to not only achieve but. to excel in graduate school His rare ability to harness that drive and allow each of us to. create a unique scientific contribution with the right mix of guidance and independence is. unparalleled It s been the privilege and opportunity of a lifetime Thanks Sensei. Of course the next thanks goes to James Haas James it s been a long haul and I. couldn t have done it without you I m looking forward to working with you in the years. ahead and drinking a few JC s along the way, I d also like to thank the other members of my committee Professor Iain Boyd. and Professor John Foster Their advice and instruction over the years has been truly. appreciated, A true testament of Alec s leadership and the remarkable learning environment he. has established was in meeting and working with his past students aka the Michigan. Mafia In addition to James and John I m grateful for the opportunity to work closely. with Brain Beal and Rich Hofer whose teachings have been invaluable As for the rest. of the older crowd I ve become friends with over the years the support for less seasoned. members of the Michigan Mafia is truly appreciated Thanks to Jesse Linnell Josh. Rovey Mitchell Walker Alan Victor Tim Smith Pete Peterson Frank Gulczinski Brad. King and even Dan Herman who told me there were too many Dans when I first joined. Then there are the peers who I ve grown along with over the years including Rob. Lobbia Kristina Lemmer Prashant Patel Brian Reid Sonca Nguyen Tom Liu and Bailo. Ngom Bryan was my cohort in crime building a certain 6 kW thruster that will remain. un named for all eternity Rob and Kristina in particular shared the growing pains of pre. lims One of my few regrets from graduate school is spending so much time away from. everyone in Ann Arbor, Of course there s Dave Floppy Kirtley We ve been through a lot in a few short.
years from traveling to the highest point in Africa to getting robbed at knife point in the. streets of Peru starting a business and maintaining sanity at Domingo s Good times. To the younger PEPL crew Rohit Shastry Mike McDonald David Huang Ray. Liang Adam Shabshelowitz Laura Spencer and Roland Florenz the PEPL tradition you. inherit is truly exceptional I ve enjoyed getting to know you on my brief stints back in. Ann Arbor and hope I can help future PEPL generations as well as my predecessors have. None of this would have been possible without the long distance administrative. help from a few hard working ladies back in Michigan I d like to thank Denise Phelps. for keeping me on course and especially helping me get a Ph D in Aerospace. Engineering as opposed to Aerospace Science Denise Edmund went above and beyond. in helping me complete the final Rackham degree requirements Colleen Root is much. appreciated for all her work scheduling meetings with Alec Last but not least is. Margaret Fillion who is one of a kind, Previous PEPL graduates have described their time at AFRL as filled with. freedom and frustration or more succinctly as purgatory All are true descriptions but. the group of friends and colleagues help overshadow most of the shortcomings A. special thanks to Bill Larson Justin Koo and Michelle Scharfe for many fruitful. discussions and patience when I used you as a sounding board Bill also deserves tribute. for his vital contributions to the Hall thruster efficiency architecture in Chapter 2 Garrett. Reed deserves special recognition for developing an automated DAQ system for. Chamber 3 Thanks to Bill Hargus and Mike Nakles for assistance with Chamber 1 and. to Daron Bromaghim for advice on STINFO related issues. Then there s the AFRL support staff I gratefully acknowledge Skip Skipworth. John Morrow Bob Gregory and Tom Glover for their continual maintenance and. resuscitation of Chamber 3 Linda Skipworth Rosa Ritter Eva Lawson and Lynn. Hutchison I can t imagine where this place would be without you Thanks for all the. things that you do to keep us going on a daily basis. I express gratitude to my advisors and mentors at the University of Washington. specifically Denice Denton and Mark Campbell Denice gave me the opportunity to. begin experimental research during my first quarter as a freshman and was instrumental. in my early undergraduate years She was a special advisor who continually provided. pathways for further growth and did everything in her means to enable students to realize. their full potential Mark is a mentor who gave his students the same trust and respect he. would to a professor and in the process makes people want to work harder for him. Thanks for allowing a 20 year old kid to play with flight hardware even if it never got off. the ground In addition I d like to thank my good friends at the University of. Washington Ruchi and Nels whose support and guidance was beyond measure. My family has shown tremendous support over the years each in their own way. I m not sure any of you understand what I do but your love and encouragement made all. the difference I m grateful to my Mom and Dad for the love the foundation and the. freedom they have always provided I can t express in words what it s meant to me I d. like to thank my brother Steve for his sound advice and always keeping things in. perspective There are too many people to name but thank you all. Lastly I want to thank my wife Katie She s dedicated these last months to. helping me focus solely on finishing this degree and I can t imagine how much more. difficult it would be without her enduring love and support Katie I told you I had. about a year left when we started dating It s taken a slightly longer than that but I. can t wait to begin the next phase of our lives together Thank you. Daniel Lucas Brown,aka DB Bearded Oso de la Noche,Table of Contents. Acknowledgements ii,List of Figures x,List of Tables xxii. List of Appendices xxiii,Nomenclature xxiv,Abstract xxxii. Chapter 1 Introduction 1,1 1 Fundamentals of Space Propulsion 2.
1 2 Electric Propulsion Thruster Technologies 6,1 2 1 Electrothermal Propulsion 6. 1 2 2 Electromagnetic Propulsion 6,1 2 3 Electrostatic Propulsion 7. 1 3 Hall Effect Thruster Overview 9,1 3 1 Hall Thruster Physics 10. 1 3 2 Hall Thruster Design Considerations and Operation 11. 1 4 Motivation 13,1 5 Contributions of Research 15. 1 6 Organization 19, Chapter 2 Hall Thruster Efficiency Architecture 22.
2 1 Historical Perspective and Recent Methodologies 23. 2 2 Development of a Hall Thruster Efficiency Architecture 26. 2 2 1 Formulation of Thrust 27,2 2 2 Decomposing Total Thruster Efficiency 31. 2 2 3 Propellant Efficiency 32,2 2 3 1 Charge Utilization 33. 2 2 3 2 Mass Utilization 35,2 2 3 3 Neutral gain Utilization 37. 2 2 4 Energy Efficiency 39,2 2 4 1 Voltage Utilization 40. 2 2 4 2 Current Utilization 42,2 2 5 Beam Efficiency 44.
2 3 Performance Parameters 49, 2 3 1 Voltage Exchange and Mass Exchange Parameters 49. 2 3 2 Specific Impulse and Thrust to Power Ratio 51. 2 3 3 Energy Losses and Ionization Cost of a Multiply Charged Plasma 51. 2 4 Application to Experimental Results 53,2 5 Summary 54. Chapter 3 Experimental Apparatus 56,3 1 Vacuum Facilities 57. 3 1 1 Chamber 1 at AFRL 57, 3 1 1 1 Power Electronics and Propellant Hardware 59. 3 1 1 2 Diagnostic Positioning System 60,3 1 2 Chamber 3 at AFRL 61.
3 1 2 1 Power Electronics and Propellant Hardware 64. 3 1 2 2 Thruster Telemetry and Data Acquisition System 66. 3 1 2 3 Diagnostic Positioning Systems 67,3 2 Laboratory Hall Effect Thruster 69. 3 3 Performance and Plume Diagnostics 71,3 3 1 Inverted Pendulum Thrust Stand 71. 3 3 2 Langmuir Probe 73,3 3 3 Retarding Potential Analyzer 76. 3 3 4 ExB Probe 83,3 3 5 Faraday Probes 93,3 3 5 1 Nude Faraday Probe 93. 3 3 5 2 Nested Faraday Probe 95,3 4 Summary 102, Chapter 4 Evaluation of Faraday Probe Design and Scattering Effects 103.
4 1 Past Investigations 104, 4 2 Measurement Coordinate System Effects and Correction Factors 107. 4 2 1 Angle of Beam Ions to Probe Face 108,4 2 2 Distance of Beam Ions to Probe Face 113. 4 2 3 Faraday Probe Angle and Distance Correction Factors 117. 4 2 4 Additional Spatial Measurement Uncertainty 119. 4 3 Examination of Faraday Probe Design and Geometry 120. 4 3 1 Comparison of Nested Faraday Probe Current Density Profiles 120. 4 3 2 Gap Correction Factor for the Effective Projected Collection Area 124. 4 3 3 Effects of Non uniform Bias Potential 131, 4 3 4 Applying the Gap Correction Factor to Past Results 138. 4 4 Analysis of Ion Plume Scattering and Facility Effects 145. 4 4 1 Determination of Vacuum Current Density Profiles 146. 4 4 2 Analysis of Ion Migration in the Plume 155, 4 4 3 Comparison of Ion Migration Results With Numerical Simulations 161. 4 4 4 Calculation of Vacuum Beam Divergence 164, 4 5 Recommendations for High Accuracy Current Density Profiles 169.
4 6 Summary and Conclusions 172, Chapter 5 Characterization of Low Voltage Hall Thruster Operation 176. 5 1 Facility Effects on Thruster Performance and Beam Formation 177. 5 1 1 Thrust and Discharge Current 178,5 1 2 Ion Current and Plume Expansion 184. 5 2 Thruster Performance Measurements 199,5 2 1 Current Voltage Characteristics 199. 5 2 2 Thrust and Performance 200,5 2 3 Thruster Discharge Oscillations 203. 5 3 Far field Plume Measurements 209, 5 3 1 Current Density Profiles and Ion Beam Current 209.
5 3 2 Ion Energy per Charge Distributions 213, 5 3 3 Ion Species Current Fractions and Mass Flow Fractions 216. 5 4 Low Discharge Voltage Hall Thruster Loss Mechanisms 220. 5 4 1 Evaluation of Performance Parameters 220,5 4 2 Performance Utilization Efficiencies 225. 5 4 2 1 Beam Efficiency 227,5 4 2 2 Propellant Efficiency 231. 5 4 2 3 Energy Efficiency 235, 5 4 3 Ionization Processes and Joule Heating Losses 237. 5 5 Summary 247, Chapter 6 Low Discharge Voltage Thruster Operating Regimes 251.
6 1 Visualization of Low Discharge Voltage Operating Regimes 253. 6 2 Mapping Thruster Operation for Anode and Cathode Flow Rate 255. 6 3 Discharge Oscillations of Low Voltage Operating Regimes 261. 6 4 Far field Plume Measurements 267,6 4 1 Ion Beam Current and Plume Divergence 267. 6 4 2 Plasma Potential and Electron Temperature 270. 6 4 3 Distributions of Ion Energy and Ion Energy per Charge 275. 6 5 Variation in Near field Neutral Density 284, 6 6 Potential Causes of Low Discharge Voltage Operating Regimes 290. 6 6 1 Thruster Ionization Instabilities 290,6 6 2 Cathode Induced Discharge Oscillations 291. 6 6 3 Discharge Power Supply Oscillations 294,6 7 Summary 294. Chapter 7 Summary and Concluding Remarks 296, 7 1 Low Discharge Voltage Hall Thruster Loss Mechanisms 297.
7 2 Low Discharge Voltage Hall Thruster Operating Regimes 299. 7 3 Facility Effects and Formation of the Jet mode Plume Structure 300. 7 4 Evaluation of Faraday Probe Design and Analysis 302. 7 5 Development of a Hall Thruster Efficiency Architecture 305. 7 6 Recommendations for Future Work 307, 7 6 1 Analysis of Joule Heating Discharge Loss Mechanisms 307. 7 6 2 Interpretation of Low Discharge Voltage Operating Regimes 308. 7 6 3 Validation of Faraday Probe Experimental Methods and Analysis 310. 7 6 4 Improvements in Characterization of Global Performance Quantities 311. Appendices 313,Bibliography 333,List of Figures, Figure 1 1 Trade space of payload mass fraction as a function of exhaust velocity with. variations in propulsion system metrics for a maneuver with V 4000 m s. theoretical LEO to GEO transfer Variations in maneuver time specific. power and thruster efficiency are studied for the rocket equation 4. Figure 1 2 Cross sectional illustration of a conventional magnetic layer Hall thruster. with a centrally mounted cathode 12, Figure 2 1 Ionization number fraction as a function of mass utilization with lines of. constant neutral velocity ratio y0 for a singly charged plasma. Q 1 f 2 f 3 0 37, Figure 2 2 Neutral gain utilization as a function of mass utilization with variations in. reduced neutral speed from y0 0 01 to y0 0 06 for Q 1 and Q 3 which. are limiting cases for a trimodal ion population 39. Figure 2 3 Illustration of electron impact cascade ionization of singly charged and. doubly charged ions in the Hall thruster discharge 43. Figure 2 4 Variation in due to ion species composition for m 1 Lines of constant. f2 0 and f3 0 bound for a trimodal ion population and are compared. with the approximation Q 1 2 47, Figure 2 5 Representative distribution of beam current and current density at 1 meter.
radius as a function of angular position in the plume of a nominal 6 kW. laboratory Hall thruster at 300 V 20 mg s described in Chapter 3 49. Figure 3 1 Chamber 1 schematic not to scale 58, Figure 3 2 Diagnostic positioning system in Chamber 1 with R coordinate axis. control 60,Figure 3 3 Chamber 3 at AFRL RZSS 61,Figure 3 4 Chamber 3 schematic not to scale 63. Figure 3 5 Electrical diagram of power electronics in Chamber 3 for the 6 kW Hall. thruster and LaB6 cathode 64, Figure 3 6 Schematic of the Chamber 3 propellant distribution system 65. Figure 3 7 Diagnostic positioning system in Chamber 3 with coordinate axis. control 67, Figure 3 8 Diagnostic positioning system in Chamber 3 with X Y coordinate axis. control 68, Figure 3 9 Photograph of the 6 kW laboratory Hall thruster with a centrally mounted.
LaB6 cathode 70, Figure 3 10 Photograph of the 6 kW laboratory Hall thruster courtesy of JPL 70. Figure 3 11 Schematic of the 6 kW laboratory model Hall thruster illustrating locations. of propellant injection at the anode cathode and auxiliary port 71. Figure 3 12 Photograph of a 6 kW Hall thruster mounted on the inverted pendulum. thrust stand at AFRL RZSS 72, Figure 3 13 Langmuir probe trace comparing data analysis techniques used to. determine plasma potential The measurement was taken on thruster. centerline 1 meter downstream of the 6 kW HET operating at 105 V 20. mg s in Chamber 3 76, Figure 3 14 Cross sectional illustration of the RPA showing the multi grid design and. particle filtration process 77, Figure 3 15 RPA trace showing the data analysis technique used to determine the most. probable ion potential The measurement was taken on thruster centerline. 1 meter downstream of the 6 kW HET operating at 300 V 20 mg s in. Chamber 3 79, Figure 3 16 Potential diagram illustrating the relationship between measured voltages.
Vd Vcg plume measurements Vmp Vp and calculated potentials Va. Figure 3 17 Electrical diagram of RPA grid power electronics and DAQ system 82. Figure 3 18 Photograph of the ExB probe build by Plasma Controls LLC The top. cover is removed to illustrate the electromagnetic fields in ion velocity. filter and regions of ion collimation drift and collection 86. Figure 3 19 Electrical diagram of ExB probe power electronics and DAQ system 87. Figure 3 20 Normalized ExB probe trace showing the data analysis technique used to. determine ion species fractions The measurement was taken on thruster. centerline 1 meter downstream of the 6 kW HET operating at 300 V 20. mg s in Chamber 3 88, Figure 3 21 Normalized ExB probe traces on thruster centerline from 1 0 to 1 3 meters. downstream of the 6 kW HET operating at 300 V 10 mg s and 150 V 20. mg s in Chamber 3 91, Figure 3 22 Electrical diagram of the nude Faraday probe power electronics and DAQ. Figure 3 23 Top view and cross sectional diagrams of the AFRL nested Faraday probe 95. Figure 3 24 Top view of the four collection area configurations of AFRL nested. Faraday probe Regions of blue are the current collecting surfaces. orthogonal to the beam The gap between Collector 1 and Collector 2 is. equal to the gap between Collector 2 and the guard ring 96. Figure 3 25 Photograph of the AFRL nested Faraday probe shown in the 0 5 mm gap. width configuration 98, Figure 3 26 Electrical diagram of the nested Faraday probe power electronics and DAQ. Figure 3 27 Nested Faraday probe bias voltage characterization of the inner collector. left and the outer collector right for the 0 5 mm and 1 5 mm gap. configurations at 3 1x10 6 and 3 4x10 5 torr Normalized current is shown. at the location of largest Debye length in the plume at 0 degrees and the. location of smallest Debye length in the plume at 90 degrees at 8 CCDD. and 20 CCDD 101, Figure 4 1 Coordinate system for probe distance and angular location with the thruster. modeled as two point sources 108, Figure 4 2 Diagram of ion angles of incidence and relevant distances for the probe.
angular orientation in a two point source system 109. Figure 4 3 Ion angle of incidence from the left and right point sources as a function of. probe angular position with contours of constant R 2RCL 4 8 12 16 and. 20 CCDD 111, Figure 4 4 Correction factor A accounting for cosine losses in the probe collection. area as a function of angular position with contours of constant R 2RCL 4. 8 12 16 and 20 CCDD 111, Figure 4 5 Correction factor A accounting for cosine losses in the probe collection. area on channel centerline 90 as a function of downstream thruster. diameters R 2RCL 112, Figure 4 6 Diagram of the relevant angles and distances to characterize probe distance. to the left and right ion point sources 114, Figure 4 7 Probe distance from the left and right point sources relative to the. measurement radius R as a function of probe angular position with. contours of constant R 2RCL 4 8 12 16 and 20 CCDD 115. Figure 4 8 Correction factor D accounting for the probe distance to the left and right. ion point sources as a function of angular position with contours of. constant R 2RCL 4 8 12 16 and 20 CCDD 115, Figure 4 9 Probe distance from the left and right ion point sources relative to the.
measurement radius R as a function of downstream thruster diameters. R 2RCL at 0 and 90 116, Figure 4 10 Combined effect of correction factors D A accounting for the probe. distance and angle with respect to the left and right ion point sources as a. function of angular position with contours of constant R 2RCL 4 8 12. 16 and 20 CCDD 117, Figure 4 11 Combined effect of the correction factors D A on channel centerline. 90 as a function of downstream thruster diameters R 2RCL 118. Figure 4 12 Normalized current density profiles from Collector 1 and Collector 1 2 for. the 0 5 mm and 1 5 mm gap configurations measured at 8 12 16 and 20. CCDD with a facility background pressure of 3 1x10 6 torr 121. Figure 4 13 Comparison of collector area ratios and collected current ratios of the 0 5. mm configuration top 1 5 mm configuration middle and Collector 1. bottom at 3 1x10 6 1 0x10 5 and 3 4x10 5 torr measured at 8 12 16 and. 20 CCDD as a function of probe angular position 123. Figure 4 14 Illustration of ions collected by the side walls of the nested Faraday probe. and the increase in projected collection area 125, Figure 4 15 Diagram of the nude Faraday probe collector outer radius Rc height hC. guard ring inner radius RGR height hGR and gap width g 126. Figure 4 16 Comparison of corrected and uncorrected collector area ratios and. collected current ratios of the 0 5 mm configuration top 1 5 mm. configuration middle and Collector 1 bottom at 3 1x10 6 1 0x10 5 and. 3 4x10 5 torr measured at 8 12 16 and 20 CCDD as a function of probe. angular position 129, Figure 4 17 Normalized current density profiles corrected with G from Collector 1. and Collector 1 2 for the 0 5 mm and 1 5 mm gap configurations. measured at 8 12 16 and 20 CCDD with a facility background pressure of. 3 1x10 6 torr 130, Figure 4 18 Normalized current to Collector 1 in the 0 5 mm gap configuration.
Configuration 1 as a function of bias potential on Collector 2 and the. guard ring Measurements are normalized to the maximum centerline. current for 0 V on the guard ring and are shown from 50 to 130 in. 10 increments at 20 CCDD with a facility background pressure of 3 1x10 6. Figure 4 19 Normalized current to Collector 1 2 in the 0 5 mm gap configuration. Configuration 2 as a function of bias potential on the guard ring. Measurements are normalized to the maximum centerline current for 0 V. on the guard ring and are shown from 50 to 130 in 10 increments at. 20 CCDD with a facility background pressure of 3 1x10 6 torr 135.

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