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Investigation of a Space Propulsion Concept Using Inertial Electrostatic Confinement

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Investigation of a Space Propulsion Concept Using Inertial Electrostatic Confinement © 2018 Drew Ahern INVESTIGATION OF A SPACE PROPULSION CONCEPT USING INERTIAL ELECTROSTATIC CONFINEMENT BY DREW AHERN DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Aerospace Engineering in the Graduate College of the University of Illinois at Urbana-Champaign, 2018 Urbana, Illinois Doctoral Committee: Emeritus Professor George H. Miley, Chair Emeritus Professor Rodney L. Burton Assistant Professor Davide Curreli Professor Deborah Levin Professor David N. Ruzic Abstract This thesis discusses the Helicon Injected Inertial Plasma Electrostatic Rocket (HIIPER), a space propulsion concept consisting of a helicon source for plasma generation and an ion extraction method using a nested pair of inertial electrostatic confinement (IEC) grids that are asymmetrically designed. In this study, which used argon as a propellant, a retarding potential analyzer (RPA) was used to measure the exhaust of HIIPER, and results showed the presence of electrons and ions, with ion energies equal to the helicon bias voltage and electron energies on the order of the inner IEC grid voltage. Electron energy distributions were also generated. Quasineutral exhaust conditions were measured to occur with the inner IEC grid between 2 and 3 kV (negative). Tests on the IEC grid configuration were also performed, which indicated that electrons preferentially exited the asymmetry of the inner IEC grid. Langmuir probe measurements showed that some ion losses occurred due to the experimental setup. These losses were reflected in thrust measurements at the exhaust of only a few micronewtons. However, with improvements to the facilities and experimental setup, improvements in thruster efficiency would likely be obtained. While additional analysis would be required to fully characterize HIIPER, the results thus far show promising quasineutral behavior and demonstrate an innovative cathode design for electric propulsion applications. ii Acknowledgements I would like to thank my advisor Professor George Miley for all of his guidance and help these past several years. I am very grateful for his technical expertise and advice, as well as his patience in our discussions on the project, which provided thoughtful feedback that allowed me to keep moving forward. Additionally, I am very grateful for his financial support through this past year and for purchasing equipment for the lab. I would also like to thank the members of my committee for their help and support throughout this endeavor: Professor Rodney Burton, Professor Davide Curreli, Professor Deborah Levin, and Professor David Ruzic. I am very grateful for all of their time and advice. I would also like to thank past and present fellow grad students who worked with me and helped me learn the ropes: Benjamin Bercovici, George Chen, Paul Keutelian, Akshata Krishnamurthy, Mruthun Thirumalaisamy, Ben Ulmen, and Erik Ziehm. Additionally, I would like to thank all of the undergrads who made these results a success: Waleed Ahmed, Hussein Al- Rashdan, Oguzhan Altun, Grant Berland, Adam Blythe, Jared Bowman, Emil Broemmelsiek, Zhengyu Chen, Patchara Choakpichitchai, Zongxu “Rick” Dong, Patrick Drew, Branden Kirchner, Guillermo Perez, Nicklaus Richardson, Kyle Stanevich, Nicholas St.Lawrence, Albert Valiaveedu, and Tim Wheeler. (I hope I remembered everyone!) The HIIPER Lab has been generously supported by several groups. I would like to thank the Air Force Research Lab (AFRL) for charitably loaning and ultimately donating helicon equipment and other devices. Partial financial support provided by AFRL, NASA, National Systems Corporation, and NPL Associates of Champaign, IL is also greatly appreciated. iii From Professor Ruzic’s group, I would like to thank Michael Christenson and Pawel Piotrowicz for their assistance in understanding Langmuir probes and RPAs, as well as lending me lab equipment. I would also like to thank the machinists in the AE and ECE machine shops for their expertise, advice, and skill in the manufacturing of various components used in this thesis: Lee Booher, Steve Mathine, and Greg Milner of the AE machine shop, and Scott McDonald and the other machinists of the ECE machine shop. Throughout my long time here, I have been fortunate to have had great support as a graduate student. I would like to thank the AE graduate coordinator Staci McDannel for all of her help these past few years. Additionally, I would like to thank Laura Gerhold, Professor Phillipe Geubelle, Diane Jeffers, and Kendra Lindsey of the AE Department, and Barbara Russell of the NPRE Department for all of the various grad-related issues that have popped up over the years. As a grad student, I was supported by various teaching and research assistantship opportunities. I would like to thank Professor Burton, the late Professor Steve D’Urso, and Professor Geubelle of the AE Department, and Elisabeth Jenicek of the U.S. Army Corps of Engineers Construction Engineering Research Lab in helping support my graduate student career. I would also like to thank my master’s adviser Professor Burton for getting me started in grad school at Illinois and for his mentorship throughout my master’s degree. Additionally, I would like to thank the Electric Propulsion Systems branch chief Dave Jacobson, my NASA Pathways mentors Hani Kamhawi, Peter Peterson, and Rob Thomas, and the NASA Pathways Office of the Glenn Research Center for giving me something to look forward to after grad school. iv Aside of being a graduate student working on school, I have been extremely fortunate to have had very good friends, and I would like to thank them for their friendship and laughter throughout the years. Last but certainly not least, I would like to thank my parents for their unconditional love and support, as I owe them everything that I am and have achieved. v Table of Contents List of Figures ................................................................................................................................. x List of Tables ................................................................................................................................ xv Nomenclature ............................................................................................................................... xvi Chapter 1 Introduction ............................................................................................................... 1 1.1 Introductory material ........................................................................................................ 1 1.1.1 Main idea .................................................................................................................. 1 1.1.2 Thesis outline ............................................................................................................ 2 1.2 The ion thruster [1] ........................................................................................................... 2 1.3 Helicon thruster history .................................................................................................... 4 1.4 Research goal ................................................................................................................... 9 Chapter 2 Background ............................................................................................................. 10 2.1 Inertial electrostatic confinement ................................................................................... 10 2.1.1 IEC fusion ............................................................................................................... 10 2.1.2 Types of discharges................................................................................................. 12 2.2 Helicon plasmas ............................................................................................................. 15 2.2.1 Helicon theory ......................................................................................................... 15 2.2.2 Ionization efficiency explanation ............................................................................ 19 2.2.3 Degree of ionization and doubly ionized population .............................................. 20 Chapter 3 Experimental setup.................................................................................................. 22 vi 3.1 Experimental facilities.................................................................................................... 22 3.2 IEC grid setup................................................................................................................. 27 3.3 Langmuir probe .............................................................................................................. 28 3.3.1 Theory of operation................................................................................................. 29 3.3.2 Probe construction and frequency response ............................................................ 34 3.4 Mach probe ..................................................................................................................... 35 3.4.1 Mach probe theory .................................................................................................. 36 3.4.2 Construction ............................................................................................................ 38 3.5 Retarding potential analyzer (RPA) ............................................................................... 39 3.5.1 RPA theory.............................................................................................................
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