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Advanced Cathodes for Next Generation Electric Propulsion Technology Air Force Institute of Technology AFIT Scholar Theses and Dissertations Student Graduate Works 3-7-2008 Advanced Cathodes for Next Generation Electric Propulsion Technology Dustin J. Warner Follow this and additional works at: https://scholar.afit.edu/etd Part of the Aerospace Engineering Commons Recommended Citation Warner, Dustin J., "Advanced Cathodes for Next Generation Electric Propulsion Technology" (2008). Theses and Dissertations. 2702. https://scholar.afit.edu/etd/2702 This Thesis is brought to you for free and open access by the Student Graduate Works at AFIT Scholar. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of AFIT Scholar. For more information, please contact [email protected]. ADVANCED CATHODES FOR NEXT GENERATION ELECTRIC PROPULSION TECHNOLOGY THESIS Dustin J. Warner, 2nd Lieutenant, USAF AFIT/GA/ENY/08-M07 DEPARTMENT OF THE AIR FORCE AIR UNIVERSITY AIR FORCE INSTITUTE OF TECHNOLOGY Wright-Patterson Air Force Base, Ohio APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED The views expressed in this thesis are those of the author and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the U.S. Government. AFIT/GA/ENY/08-M07 ADVANCED CATHODES FOR NEXT GENERATION ELECTRIC PROPULSION TECHNOLOGY THESIS Presented to the Faculty Department of Aeronautics and Astronautics Graduate School of Engineering and Management Air Force Institute of Technology Air University Air Education and Training Command In Partial Fulfillment of the Requirements for the Degree of Master of Science in Astronautical Engineering Dustin J. Warner, BS 2nd Lieutenant, USAF March 2008 APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED AFIT/GA/ENY/08-M07 Abstract The research presented here investigated the feasibility of 6.4 mm Lanthanum Hexaboride (LaB6) and Cerium Hexaboride (CeB6) hollow cathodes for low power electric propulsion applications (100-300W). Two orifice geometries, one anode configuration, several anode and keeper currents, and a range of xenon flow rates were tested for the LaB6 cathode. The CeB6 cathode underwent the same tests, with the exception of the second orifice geometry due to time constraints. An oscilloscope measured waveform behavior and a single Langmuir probe for plasma properties. Infrared imaging studied the thermal characteristics of both cathodes and electron microscopy for surface contaminant analysis. High-speed imaging provided visual data for coupling plasma observations. The CeB6 cathode operated in spot mode as low as 1.5 A and 1.5 sccm with no heater or keeper power, and as high as 6 A, 1.5 sccm with 1 A keeper current. The CeB6 cathode was more susceptible to poisoning than the LaB6 cathode. It also operated at slightly higher temperatures. The LaB6 cathode was not affected by poisoning and ran in spot mode as low as 2.5 A, at 1.5 sccm with no heater or keeper power. When the aspect ratio was reduced to 0.25, the cathode operated as low as 1.4 A, with 1.5 sccm. The same spot/plume mode characteristics were observed for LaB6 as CeB6. The study of both cathodes is presented here including suggestions for a 3 mm LaB6 cathode. iv Acknowledgments First, I would like to thank God for the work I have completed and the things I have learned in this research and this period of my life, words cannot express my true gratitude. I would also like to thank my wife for her patience and understanding while I completed this work; her support deserves more recognition than I can offer. My advisor, Richard Branam, was ambitious enough to push forward into a new avenue of research for AFIT and did not let the unknown stop our endeavor. Without this approach, I may not have accomplished the work presented here. During my initial investigations, Dan Goebel was very gracious to allow me to use his design and save me from many long hours of searching. John Williams was also keen to point out some fundamental details and concepts that were crucial to my original brainstorming that prevented me from wandering down the wrong path. Thanks to AFRL for funding this research and the facilities required for it. Jay Anderson, John Hixenbaugh, Wilber Lacy, and Barry Page were all very instrumental in establishing the infrastructure necessary for these experiments. They also helped to troubleshoot any problems and a couple came in late to make sure things ran smoothly. Of course, Bill Hargus spawned the origin of the concept of this work. He suggested something he thought would present a challenge for us and a unique learning opportunity- of which it did. Finally, Dr. Glen Perram of the physics department at AFIT was so gracious to let us borrow his Langmuir Probe in short notice. Without his generosity, I would have a lot less to write about here. Dustin J. Warner v Table of Contents Page Abstract .............................................................................................................................. iv Acknowledgments................................................................................................................v Table of Contents ............................................................................................................... vi List of Figures .................................................................................................................. viii Nomenclature .....................................................................................................................15 I. Introduction ...................................................................................................................16 Motivation ..................................................................................................................16 Problem Statement ......................................................................................................17 Research Objectives ...................................................................................................17 Research Focus ...........................................................................................................18 Investigative Questions ..............................................................................................19 II. Literature Review ..........................................................................................................19 Hall Thruster Applications .........................................................................................19 Ion Thruster Applications ...........................................................................................21 Plasma Contactor Applications ..................................................................................23 Cathode Technology ...................................................................................................24 Hollow Cathode Operation and Physics .....................................................................28 Boride Cathodes .........................................................................................................36 Experimental Considerations ......................................................................................39 III. Methodology ................................................................................................................41 Vacuum Facility .........................................................................................................41 Hollow Cathode Assembly .........................................................................................43 vi Test Assembly ............................................................................................................51 Data Acquisition and Measurement Equipment .........................................................53 Langmuir Probe ..........................................................................................................55 Infrared Imaging .........................................................................................................60 Microscope Imaging ...................................................................................................62 High-Speed Imaging ...................................................................................................64 Cathode Operation Test Points ...................................................................................64 IV. Analysis and Results ....................................................................................................65 Cathode Ignition .........................................................................................................65 Spot and Plume Mode Characterization .....................................................................68 Infrared Imaging Analysis ........................................................................................116 Poisoning Mechanisms .............................................................................................127 High-Speed Imaging Results ....................................................................................136 V. Conclusions and Recommendations ..........................................................................139 Conclusions of Research ..........................................................................................139 Recommendations for Future Research ....................................................................143 Appendix A. Spectral Analysis Data ..............................................................................147
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