DESIGN AND CONSTRUCTION OF A THREE HUNDRED kA BREECH SIMULATION RAILGUN by BRETT D. SMITH, B.S. in M.E. A THESIS IN -ELECTRICAL ENGINEERING Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN ELECTRICAL ENGINEERING Jtpproved Accepted December, 1989 ACKNOWLEDGMENTS I would like to thank Dr. Magne Kristiansen for serving as the advisor for my grad­ uate work as well as serving as chairman of my thesis committee. I am also appreciative of the excellent working environment provided by Dr. Kristiansen at the laboratory. I would also like to thank my other two thesis committee members, Dr. Lynn Hatfield and Dr. Edgar O'Hair, for their advice on this thesis. I would like to thank Greg Engel for his help and advice in the design and construc­ tion of the experiment. I am grateful to Lonnie Stephenson for his advice and hard work in the construction of the experiment. I would also like to thank Danny Garcia, Mark Crawford, Ellis Loree, Diana Loree, and Dan Reynolds for their help in various aspects of this work. I owe my deepest appreciation to my parents for their constant support and encour­ agement. The engineering advice obtained from my father proved to be invaluable. 11 CONTENTS .. ACKNOWLEDGMENTS 11 ABSTRACT lV LIST OF FIGURES v CHAPTER I. INTRODUCTION 1 II. THEORY OF RAILGUN OPERATION 4 III. DESIGN AND CONSTRUCTION OF MAX II 27 Railgun System Design 28 Electrical Design and Construction 42 Mechanical Design and Construction 59 Diagnostics Design and Construction 75 IV. MAX II OPERATION 89 v. EXPERIMENTAL RESULTS 97 VI. CONCLUSIONS 118 LIST OF REFERENCES 120 111 ABSTRACT The objective of this project was to build a rail gun materials test bed which could be used for the relatively quick and inexpensive testing of promising rail and insulator materials. This report discusses the design, construction, operation and testing of the rail- gun facility. The facility is called MAX II which stands for Moving Arc Experiment II. The basic design requirements of the railgun system were decided upon first. These requirements included, among others, a minimum peak rail linear current density of 300 .kNcm and projectile velocities in the range from 500-2,000 m/s. A crowbarred RLC cir­ cuit was chosen as the power system for driving the rail gun. A model of the power sys­ tem and the railgun ballistics was developed and used to determine appropriate system parameters. Each component of the system was then carefully designed to withstand the large magnetic forces which exist in the railgun system. Upon completion of the con- struction of the facility, a series of ten test shots were made in order to determine the abil- ity of the system to meet the design requirements. It was found that the system could meet these design requirements. Improvements to the system were also recommended. The materials problems which presently plague railgun technology must be addressed in order for the use of rail guns to become practical. The testing of new rail and insulator materials is therefore essential in the development of rail gun technology. The MAX II facility should prove to be a helpful tool in the testing and development of these new materials. IV LIST OF FIGURES 2.1 Railgun System Diagram 5 2.2 Ideal Railgun 7 2.3 Railgun Circuit Model 12 2.4 Railgun With RLC Power Circuit 14 2.5 Railgun With Crowbarred RLC Power Circuit 16 2.6 Rogowski Coil Diagram 20 2. 7 Rogowski Coil Circuit Model 21 2.8 Rogowski Coil Circuit Model With Integrator 23 2.9 B Dot Probe Configuration 25 3.1 Railgun Bore Configuration 30 3.2 Circuit Diagram For Simplified Model 35 3.3 Sample Model Armature Current 39 3.4 Sample Model Projectile Velocity 40 3.5 Sample Model Projectile Displacement 41 3.6 Picture Of Capacitor Bank 45 3. 7 Picture Of Capacitor Bank Fault Protection 46 3.8 Elementary Ignitron 47 3.9 lgnitron Trigger Generator Schematic 49 3.10 Ignitron Pulse Generator Schematic 50 3.11 Ignitron Trigger Circuit Block Diagram 51 v 3.12 Picture Of Voltage Probe And Pulse Transformer For Ignitron Trigger 52 3.13 Picture Of Trigger Generator And Pulse Generator 53 3.14 Ignitron Tube Configuration 54 3.15 Picture Of Ignitron Tube Setup 55 3.16 Schematic Of Parallel Plate Railgun Connections 57 3.17 Picture Of Parallel Plate Railgun Connections 58 3.18 Railgun System Equivalent Circuit 60 3.19 Simulated Capacitor Bank Voltage For VP(O) = 4.2 kV (Uncrowbarred) 61 3.20 Simulated Armature Current For VP(O) = 4.2 kV (Uncrowbarred) 62 3.21 Simulated Capacitor Bank Voltage For Vp(O) = 5.8 kV (Uncrowbarred) 63 3.22 Simulated Armature Current For Vp(O) = 5.8 kV (Uncrowbarred) 64 3.23 Simulated Capacitor Bank Voltage For VP(O) = 4.2 kV (Crowbarred) 65 3.24 Simulated Armature Current For VP(O) = 4.2 kV (Crowbarred) 66 3.25 Simulated Capacitor Bank Voltage For Vp(O) = 5.8 kV (Crowbarred) 67 3.26 Simulated Armature Current For Vp(O) = 5.8 kV (Crowbarred) 68 3.27 Drawing Of Muzzle End View Of Rail gun 70 3.28 Side View Picture Of Railgun 71 3.29 Rail And Insulator Sample Drawing 72 3.30 Picture Of Breech Flange 73 3.31 Picture Of Muzzle Flange 74 3.32 Picture Of Parallel Plate Support Structure 76 3.33 Picture Of Rogowski Coil 77 Vl 3.34 Integrator Simulation Circuit 79 3.35 Simulated Armature Current For Integrator Test 80 3.36 Simulated Measured Armature Current For Integrator Test 81 3.37 Picture Of B Dot Probes For Sensing Rail And Armature Current 82 3.38 Picture Of B Dot Probes For Sensing Armature Current 83 3.39 B Dot Probe Mounting Detail 84 3.40 Break-wire Schematic Representation 86 3.41 Break-wire Circuit 87 3.42 Picture Of Break-wire System 88 4.1 Picture Of Hydraulic Stud Tensioners 90 4.2 Picture Of Hydraulic Pump 91 4.3 Projectile Drawing 93 4.4 Picture Of Projectile With Fuse Strip In Place 94 4.5 Picture Of Catch Tank 96 5.1 Capacitor Bank Voltage Trace For Fourth Shot 98 5.2 Armature Current Trace For Fourth Shot 99 5.3 Armature Current Trace For Fifth Shot 101 5.4 Composite Armature Current And B Dot Traces For Fifth Shot 102 5.5 Break-wire Trace For Seventh Shot 103 5.6 Armature Current Trace For Ninth Shot 105 5.7 Composite Armature Current And B Dot Traces For Ninth Shot 106 5.8 Break-wire Trace For Ninth Shot 107 • 0 Vll 5.9 Armature Current Trace For Tenth Shot 109 5.10 B Dot Probe #1 Trace For Tenth Shot 110 5.11 B Dot Probe #2 Trace For Tenth Shot 111 5.12 B Dot Probe #3 Trace For Tenth Shot 112 5.13 Composite Armature Current And B Dot Traces For Tenth Shot 113 5.14 Break-wire Trace For Tenth Shot 114 Vlll CHAPTER I INTRODUCfiON The use of electromagnetic forces to accelerate projectiles is an attractive technol­ ogy with several practical applications. The railgun is one of these applications. The rail- ..... gun uses the Lorentz (J x -B) force to accelerate projectiles, unlike conventional guns which use the expansion of combustion products. Because of inherent velocity limits in the expansion of gases, projectiles fired from conventional guns are limited in velocity to the 500-1300 m/s range [1]. Railguns, however, do not suffer from this limitation. Muzzle velocities as high as 20,000-50,000 m/s have been theorized as obtainable while velocities in the 6,000-7,000 m/s range have been reported [2]. The relatively high veloci­ ties obtainable by railguns make them a promising means for the advancement of gun technology. Problems, however, have been encountered in the development of rail guns. One such problem is poor efficiency. It has been shown that under ideal conditions only half of the energy delivered to the railgun goes into kinetic energy of the projectile [3] while experimental results show typic-al efficiencies of existing railguns to be less than 30 per cent (usually less than 15 per cent). This poor efficiency has hurt the chances of rail guns to be deployed in space as part of the SDI program. Another problem encountered in the development of rail guns is that the high veloci­ ties predicted early in the development have not been achieved. One explanation offered 1 2 on this problem described the arc restrike well behind the projectile as the major cause of velocity restrictions [2]. This arc restrike is in tum blamed on bore material ablation. There are, however, promising approaches under investigation for resolution of this prob­ lem. The bore materials, two conducting rails and two side wall insulators, used in rail­ guns present another problem which needs to be solved before railgun technology can become practical. The railgun bore environment is a harsh one. Bore pressures can be as high as 414 MPa (60,000 psi) with plasma temperatures as high as 30,000° K [2]. Materi­ als used in railgun bores must not only withstand mechanical and thermal loadings induced by this environment, but must also retain good electrical properties during operation. Material ablation causes the need for most existing railgun bores to be either honed or taken apart and cleaned after only a very few shots. This mode of operation is not satisfactory for practical use. New materials must be found which can survive the mechanical loads while resisting material ablation and maintaining good electrical prop­ erties.