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Experimental and Computational Studies of Electric Thruster Plasma

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Experimental and Computational Studies of Electric Thruster Plasma Experimental and Computational Studies of Electric Thruster Plasma Radiation Emission by Murat C¸elik B.S., Aerospace Engineering and Physics, University of Michigan, 2000 M.S., Aeronautics, California Institute of Technology, 2001 Submitted to the Department of Aeronautics and Astronautics in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY May 2007 c Massachusetts Institute of Technology 2007. All rights reserved. Author......................................................................................... Department of Aeronautics and Astronautics May 14, 2007 Certified by..................................................................................... Manuel Mart´ınez-S´anchez Professor, Aeronautics and Astronautics Thesis Supervisor Certified by..................................................................................... Oleg Batishchev Principal Research Scientist, Aeronautics and Astronautics Thesis Supervisor Read by........................................................................................ Daniel Hastings Professor, Aeronautics and Astronautics Read by........................................................................................ Vlad Hruby President, Busek Co. Inc. Read by........................................................................................ David Miller Professor, Aeronautics and Astronautics Accepted by.................................................................................... Jaime Peraire, Professor of Aeronautics and Astronautics Chair, Committee on Graduate Students 2 Experimental and Computational Studies of Electric Thruster Plasma Radiation Emission by Murat C¸elik Submitted to the Department of Aeronautics and Astronautics on May 14, 2007, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Abstract Electric thrusters are being developed for in-space propulsion needs of spacecraft as their higher specific impulse enables a significant reduction in the required propellant mass and allows longer duration missions. Over the last few decades many different electric propul- sion concepts have been proposed and studied. In studying the electric thrusters, in order to improve the thruster performance as well as to understand the underlying physics of thruster’s operation, various diagnostics methods were employed. As one unique method, emission spectroscopy provides a non-invasive, fast and economical diagnostic allowing also the ability to access hard to reach locations. In this study, emission spectroscopy is employed as a means to determine the trends in thruster operations as well as diagnosing the plasma parameters. This study presents the spectral measurement results of three different electric thrusters and plasma sources. First, the BHT-200 Hall thruster emission spectra measurements are pre- sented for varying discharge voltage and for various regions of observation. Second, spectral measurements of a TAL type laboratory mini-Hall thruster, MHT-9, were presented. Third, radiation emission measurements of an experimental Helicon plasma source being studied to assess the possibility of using Helicon discharge as a propulsive system are presented and the trends are discussed. Two collisional-radiative (C-R) models are developed for Argon and Xenon plasmas to analyze the experimental spectra. In the C-R models, electron induced excitation, de- excitation and ionization collisions, and spontaneous radiative de-excitation transitions are simulated for neutral and singly charged ion species. The models are validated against measured spectra obtained using different experimental setups. The BHT-200 Hall thruster has insulator ceramic annular walls made of Boron-Nitride (BN). Erosion of ceramic walls is one of the major life limiting factors for Hall thrusters. Emission spectroscopy is used as a means to determine the trends in the thruster wall erosion rate 3 by measuring the radiation emission of the Boron neutral 249.68nm and 249.77nm lines. Discussion about the spectral measurements and relevant analysis are presented. Thesis Supervisor: Manuel Mart´ınez-S´anchez Title: Professor, Aeronautics and Astronautics Thesis Supervisor: Oleg Batishchev Title: Principal Research Scientist, Aeronautics and Astronautics 4 Acknowledgments I have been calling myself a student for almost as long as I can remember. I have finally come to the end of the long educational journey that I embarked on more than two decades ago. I would like to express my gratitude and appreciation to all those countless individuals who had a part in my education in all those years. First and foremost, I want to thank my parents, Mehmet and Necla, for always standing by me, supporting me in my decisions, and for believing in me. Without their support, I would not be where I am today. I would also thank other members of my family for supporting me throughout my education. I would like to specifically thank my grandfather, Osman Nuri Berber, who definitely had an effect on me being the curious person that I am; my sister, Emel, who has always been supportive of me; and my uncle, Sezai Berber, who has been a role model to me while I was growing up. I would like to thank my Ph.D. research advisor Prof. Mart´ınez-S´anchez. His guidance was invaluable throughout my years at MIT. He was always available to answer my questions and he gave me the freedom to pursue my other interests along with my doctoral research. I am thankful for that. I would like to thank my research advisor, Dr. Oleg Batischev. I am indebted to him for supporting me during the last year of my study at MIT. He brought a great deal of excitement into my research. He has always been supportive of me, and has always been the biggest encouragement to me in moments when I was most frustrated. He became a mentor and a good friend. I will always remember him being with me during the many late night experiments, and will definitely remember the oil spill in the lab. And here is a quote from one of his e-mails that will not be forgotten: “Hope floats, -O” I would also like to thank the members of my thesis committee: Professor David Miller, Dr. Vlad Hruby, and Professor Daniel Hastings. I also thank Professor Marcus Zahn for giving me the opportunity and the challenge to teach a graduate level course. He was an incredible 5 mentor to me as I had my first real academic teaching experience. I learned a lot from him. I would like to thank all those great people I met at MIT Space Propulsion Laboratory. Six years is a long time and unfortunately I won’t be able to count the names of all the people I had the good fortune of meeting at this lab. I would particularly thank Tanya for being a great friend and for helping me with the editing of this thesis, my officemates Shannon, Blaise and Dan for creating a great office environment, my ex-roommate and good friend Felix for the many interesting discussions, and my Helicon plasma research partner and good friend Justin for sharing some of the pain with me during the last year and a half and for the exciting conversations we had. Nareg, my friend, I also want to express a special thank to you for all your dedicated work in the lab helping me and others. Without your help I would not be able to do some of my experiments and I thank you for that. I would also like to thank my high school friends who became my extended family and have always been supportive of me during my years away from my home country. I also would like to thank Yu-Hui Chiu and Rainer Dressles of Air Force Research Laboratory at Hanscom for lending us the first set of spectral instruments that helped me start this doctoral research project. I also extend my thanks to Paul Pranzo of Acton Research Co. for allowing us to use the demonstration equipments. Also special thanks to people at Busek Co. for lending us the BHT-200 Hall thruster as well as the PMT detector. 6 Contents 1 Introduction 25 1.1 Electric Propulsion . 26 1.1.1 Hall Thruster . 28 1.1.2 Helicon Thruster . 29 1.2 Plasma Diagnostics . 30 1.3 Emission Spectroscopy Physics . 32 1.4 Emission Spectroscopy Setup . 32 1.5 Collisional-Radiative Model (CRM) . 38 1.6 Literature Review . 40 1.6.1 Previous Emission Spectra Measurements of Electric Thrusters and Related C-R Modeling . 40 1.6.2 Collisional-Radiative Modeling of Argon . 41 1.7 Thesis Content, Objectives and Contributions . 42 2 Plasma Radiation Emission 47 7 2.1 Line Radiation . 47 2.2 Continuum Radiation . 51 2.2.1 Bremsstrahlung Radiation . 51 2.2.2 Electron-Recombination Radiation . 53 2.2.3 Electron Cyclotron Radiation . 54 2.2.4 Blackbody Radiation . 55 3 BHT-200 Hall Thruster Spectral Measurements 57 3.1 BHT-200 Hall Thruster . 57 3.2 Experimental Setup . 58 3.2.1 Radiation Collection and Transmission . 59 3.2.2 Radiation Dispersion . 60 3.2.3 Radiation Detection . 61 3.3 BHT-200 Hall Thruster Measurement Results . 61 3.3.1 Regions of Observation . 61 3.3.2 Voltage Scan . 68 3.4 Prediction of Plasma Temperature from Line Intensity Ratio . 73 3.5 Chapter Summary . 74 4 MHT-9 Hall Thruster Spectral Measurements 79 8 4.1 MHT-9 Hall Thruster . 79 4.2 TAL vs. SPT type of Hall Thrusters . 80 4.3 Experimental Setup . 81 4.4 MHT-9 Hall Thruster Measurement Results . 82 4.4.1 Discharge Voltage Scan . 84 4.4.2 Flow Rate Scan . 84 4.4.3 Comparison of MHT-9 and BHT-200 Spectra . 87 4.5 Chapter Summary . 89 5 Spectral Measurements of a Helicon Plasma Source 91 5.1 Mini Helicon Thruster Experiment (mHTX) . 92 5.2 Experimental Setup . 94 5.2.1 Radiation Collection and Transmission . 95 5.2.2 Radiation Dispersion . 96 5.2.3 Radiation Detection . 97 5.2.4 Intensity Calibration . 97 5.3 Helicon Plasma Source Spectral Measurements . 98 5.3.1 Broad-spectrum Results . 100 5.3.2 ICP vs. Helicon Regimes . 102 5.3.3 Power Scan . 103 9 5.3.4 Flow Rate Scan . 105 5.3.5 Magnetic Field Intensity Scan . 106 5.3.6 Short vs. Long Antenna . 108 5.3.7 Copper vs.
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