ABSTRACT Title of Document: DEV DEVE LOPMENT AND TEST OF A PERMANENT MAGNET HELICON THRUSTER Michael Frank DeMaio, Jr. M.S. 2010 Directed By: Assistant Professor Raymond Sedwick, Department of Aerospace Engineering This thesis describes the development of a test facility equipped with Langmuir probe and Retarding Potential Analyzer diagnostics for helicon thruster research. A helicon thruster using permanent magnets was also designed and tested. The helicon has several advantages, but the main disadvantage is the use of electromagnets to generate the required magnetic field, requiring a high power draw. The choice of using permanent magnets is to reduce the size, cost and power required to generate high specific impulse thrust. A prototype has been designed, analyzed and tested using Argon with demonstrated specific impulse of 1400 seconds. Analysis of the variation of beam power and ion temperature in the exhaust plume with variation of input power and vacuum pressure are presented. Preliminary tests were conducted using water as a propellant. Measurement of the ion energy distribution function shows a number of peaks indicating the presence of dissociation products. DEVELOPMENT AND TEST OF A PERMANENT MAGNET HELICON THRUSTER By Michael Frank DeMaio, Jr. Thesis submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment of the requirements for the degree of Master of Science 2010 Advisory Committee: Assistant Professor Raymond Sedwick, Chair Keystone Associate Professor Chris Cadou Associate Professor Kenneth Yu © Copyright by Michael Frank DeMaio, Jr. 2010 Preface After graduating from Manhattan College with a BS in civil engineering I wanted to follow my passion so I applied to the Aerospace Department at the University of Maryland. From an outside perspective that might seem somewhat irrational or extreme, but I always had a sense of fervor for space propulsion. Looking back on the past three years as a research graduate student, I embarked academically and personally on the greatest journey of my lifetime. I never would have guessed that I would be in the position that I am today, graduating with a master’s degree in aerospace engineering and contributing to the field of space propulsion. Furthermore, I would like to thank my family, friends, the SPPL gang also known as the ‘A-team’ and foremost Dr. Ray Sedwick for making my passion a reality. ii Dedication I would like to thank and honor Dr. Sedwick for giving me the opportunity to work as his research assistant for the past 3 years. He has provided me with the knowledge, the skills and the confidence that I needed in order to become a successful aerospace engineer. I was very blessed to work with such an established and intellectual man who was not only there for me as an advisor but also as a friend in times of hardship. He has challenged me intellectually and mentally which developed my sense of well being and character. I would also like to thank my wonderful family, my grandfather and my fiancée Stephanie for supporting me over the past few years. I couldn’t have done it without them; they were always there when I needed them, in good times and in bad. I wish to thank Marissa Intelisano, an undergraduate who worked for Dr. Sedwick in assisting me with my research by designing and building the retarding field potential analyzer. I would like to thank Dustin Alinger, a graduate student at the University of Maryland, for assisting me in building and testing the Langmuir probe. I would also like to thank Jack Touart in the Electronic Development Group (EDG) for assisting me in the production of the helicon thruster. Furthermore, I would like thank everyone in the Space Power and Propulsion group for being supportive and encouraging during my time here at the University of Maryland. God Bless. iii Acknowledgments This research was funded in part by the UMD, Department of Aerospace Engineering and in part by the National Science Foundation, Award Number #0846320. “It builds character.” Thanks Ray! It sure did. Calvin and Hobbes by Will Watterson iv Table of Contents Preface....................................................................................................................................... ii Dedication................................................................................................................................ iii Acknowledgments.................................................................................................................... iv Table of Contents.......................................................................................................................v List of Figures......................................................................................................................... vii List of Tables ........................................................................................................................... ix Chapter 1: Introduction..............................................................................................................1 1.1 Motivation: Electric Propulsion Systems................................................................ 1 1.2 The Helicon Plasma Source and Thruster............................................................... 3 1.3 Previous Work ........................................................................................................ 5 1.3.1 Background................................................................................................. 5 1.3.2 Laboratory Plasmas..................................................................................... 6 1.3.3 The Modern Helicon Source....................................................................... 7 1.3.4 Helicon Thruster ......................................................................................... 9 1.4 Objectives and Approach...................................................................................... 10 Chapter 2: Helicon Modeling...................................................................................................12 2.1 Plasma Theory ...................................................................................................... 12 2.1.1 The Helicon Wave .................................................................................... 12 2.1.2 Modal Structures....................................................................................... 14 2.1.3 Antenna Coupling ..................................................................................... 15 2.1.4 Polarization ............................................................................................... 15 2.2 Helicon Waves in Confined Plasmas.................................................................... 16 2.2.1 Eigenmodes............................................................................................... 16 2.2.2 Landau Damping....................................................................................... 18 2.2.3 Trivelpiece-Gould Modes ......................................................................... 19 2.3 Current-Free Layers.............................................................................................. 22 2.3.1 Double Layer ............................................................................................ 22 2.3.2 Single Layer (Free-Standing Plasma Sheath) ........................................... 23 2.4 Loss Mechanisms and Efficiency ......................................................................... 25 2.4.1 Bremmstrahlung Radiation ....................................................................... 26 2.4.2 Ionization .................................................................................................. 27 2.4.3 Excitation .................................................................................................. 29 2.4.4 Ambipolar Diffusion................................................................................. 30 2.4.5 Efficiency.................................................................................................. 32 2.5 Summary of Chapter 2: Helicon Theory............................................................... 33 Chapter 3: Design of Experiment ............................................................................................34 3.1 Helicon Source Dimensioning .............................................................................. 34 3.2 Antenna Design..................................................................................................... 36 3.3 Magnet Design...................................................................................................... 38 3.4 Facility Setup ........................................................................................................ 42 v 3.4.1 RF Power Supply and Matching Network................................................ 43 3.4.2 RF Feedthrough ........................................................................................ 45 3.4.3 Electromagnetic Radiation........................................................................ 46 3.5 Retarding Potential Analyzer................................................................................ 47 3.5.1 Probe Description...................................................................................... 47 3.5.2 LabVIEW Interface................................................................................... 49 3.6 Langmuir Probe