Power Systems - Explosively Driven Pulsed Power - Helical Magnetic Flux Compression Generators - Engineering Assignment Help

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Preface 

This book presents a snapshot in time of the status of university research on exploY siveYdriven pulse power with an emphasis on helical flux compression generators, FCGs, in the United States in collaboration with the U.K. circa 2004. The focus of this book is on the pulsed power output of explosive systems that are comparably small in size and can compete with conventional pulsed power. This book summaY rizes the research effort started by the 5Yyear Multi Disciplinary University ReY search Initiative, MURI, on Explosively Driven Pulsed Power covering the time period from March 1998 to April 2003. Research in the area of explosive pulsed power is at the present time, 2005, ongoing at the MURI partners? laboratories. 

Under the auspices of the MURI program, which was managed by Robert J. Barker, scientists at 3 U.S. universities and one collaborating U.K. university have been conducting research that had its strength in the synergism of the wide range of topics needed to tackle the task. Under the consortium leadership by Magne Kristiansen scientists with Electronic & Electrical Engineering, Physics, MechaniY cal Engineering, and Explosives and Metallurgy background worked closely toY gether to produce the results presented in this book. Funded at a rate of U.S. $1M/year, the participating universities and departments were  ?The Center for Pulsed Power and Power Electronics° at Texas Tech University (represented by James C. Dickens, Hermann Krompholz, and Andreas A. Neuber), the Mechanical Engineering Department at Texas Tech University (Jahan Rasty), the Explosives Research / School of Mines and Metallurgy at the University of MissouriYRolla (Jason Baird and Paul Worsey), and Texas A&M University (Bruce L. Freeman). Additionally, the continuing collaboration of Texas Tech University and the UniY versity of Loughborough, UK, (Bucur M. Novac and Ivor R. Smith) has resulted in Chap. 6 of this book. Texas Tech as the lead university and UMR were the original proposers, Texas A&M was added to the effort at a later time. 

We briefly introduce in Chap. 1 explosive driven pulsed power and discuss baY sic FCG operation. We will address in Chap. 2 the operating principle of helical FCGs in more depth and present some theoretical aspects of it. Chap. 3 will eluciY date why a real FCG is always exhibiting less than ideal performance. In the folY lowing Chaps. 4 and 5, we will focus on mechanical aspects of explosively deY formed conductors and the physics of FCG operation. Starting with a simple PSpice model, Chap. 6 presents details on stateYofYtheYart generator performance modeling. We address power conditioning, the link between FCG and load, in Chap. 7 and give an overview of practical seed energy sources in Chap. 8. We fiY nally present an example of a practical explosive Pulsed Power System, PPS, and compare its performance with a conventional PPS in Chap. 9. 

Acknowledgements 

This book brings together contributions from each of the participants in, and colY laborating research groups with, the explosive driven pulsed power MURI proY gram. It is the written contributions of the individual coauthors that have given this book its valuable substance and archival content. 

The research leading to this book would not have been possible without the graduate students that were involved in the research over the years. They are in alY phabetical order: Daniel J. Dorsey, Troy L. Guy, Tammo Heeren, David J. HemY mert, Thomas A. Holt, Eric Kristiansen, Le Xiaobin, JuanYCarlos Hernandez Llambes, Mark Schmidt, and Teresa E. Tutt. 

Finally, special thanks go to Magne Kristiansen and Lynn Hatfield of Texas Tech University for their invaluable input and carefully reading the manuscript. 

Introduction 

This book summarizes the research effort started by the 5Yyear Multi Disciplinary University Research Initiative, MURI, on Explosive Driven pulsed power1 coverY ing the time period from March 1998 to April 2003. Research in the area of exploY sive pulsed power is at the present time, 2005, ongoing at the MURI partners? laboratories. The participating MURI universities and departments were  ?The Center for pulsed power and power Electronics° at Texas Tech University, the Mechanical Engineering Department at Texas Tech University, the Explosives Research / School of Mines and Metallurgy at the University of MissouriYRolla, UMR, and Texas A&M University. Additionally, the continuing collaboration of Texas Tech University and the University of Loughborough, UK, has resulted in Chap. 6 of this book. Texas Tech as the lead university and UMR were the origiY nal proposers, Texas A&M was added to the effort at a later time. 

Magnetic flux compression generators were conceived in the early 50s, one of the fathers was Andrey D. Sacharov, who proposed transforming the energy of explosives into the energy of a magnetic field in January of 1952. His suggestions were followed in the spring of 1952 with the start of early MKY1 experiments at VNIIEF (Russian Federal Nuclear Center Y AllYRussia Research Institute of ExY perimental physics). Max Fowler in the United States fired his first plate generator in 1952 using the pole pieces of a magnetron for the initial magnetic field. Many countries have since then joined in the research on Flux Compression Generators, or short FCGs (also known as Magneto Cumulative Generators, MCGs, in RusY sianYspeaking areas), with the US and Russia starting in the early 1950s. Russian work has been ongoing continually with large staffing since the late 1950?s, while the US has had on average much less effort committed during the same time peY riod. Amongst the countries that are currently using or conducting research on FCGs are: Russia, USA, China, Germany, United Kingdom, France, Sweden, ItY aly, Romania, poland, and South Africa. 

From the beginning, the major interest in the FCGs has been based on the unique properties of the High Explosives, HE, driving these devices. A glance at Fig. 1.1 reveals the uniqueness of HE as far as its specific energy is concerned. However, only the combination with the relatively short  ?discharge time° makes it 

1 This work was primarily funded by the ExplosiveYDriven power Generation MURI proY gram funded by the Director of Defense Research & Engineering (DDR&E) and manY aged by the Air Force Office of Scientific Research (AFOSR). 

Introduction 

an excellent choice as part of a pulsed power System, ppS. pulsed power in genY eral has an extremely wide range of applications in the defense related, medical, and civil world: Radar, tooth/eye/blood vessel treatment, XYray, oil well exploraY tion, etc. The challenge is always developing  ?the best° pulsed power system, ppS, for driving a given load. Depending on the set of conditions the ppS and load have to work in, the choice of  ?best° is not always immediately obvious. HowY ever, if a single (oneYtime) large electrical pulse or a pulse train in a remote locaY tion without direct access to external power sources is required, and further, if we wanted to make everything as compact//lightweight as possible, then an explosive ppS based on the FCG is the probable choice for the power source. 

A word of caution seems to be appropriate at this point. The energy densities given in Fig. 1.1 do not include the efficiency of converting the available energy into useable output energy. For instance, the capacitors and rotating machinery are very efficient (y 80%), whereas an inductive based system may only be 10 % effiY cient. The chemical energy stored in HE can indeed be released in microseconds, however due to the small conversion efficiency, it is more realistic to expect that an FCG based ppS has an H 10 times higher energy density than a capacitor based ppS. Of course, this number depends on many factors and changes continually as breakthroughs are being made on many frontiers. Nevertheless, a factor 10 proY vides us with some guidance as we look at many different ppS. 

Two important aspects of FCGs are that they are current/energy amplifiers, and require some seed energy. They work best into small inductive loads. Simply speaking, the initially established (seeded) magnetic flux in an FCG is moved into the load, while being conserved.

Operating Principle 

If magnetic field lines are cut or the magnetic field itself is compressed, work has been done on the system, and energy will be transferred from the mechanical sysY tem to the electrical system. In particular, the compression of the magnetic field by the action of an explosively driven piston is generally referred to as explosively driven magnetic flux compression. If the device is able to use this magnetic flux either directly or as electrical output to drive a remote load, then we have an exY plosiveYdriven magnetic flux compression generator or FCG, see Fig. 2.1 for a cyY lindrical FCG, which has no stator helix. In this instance, the chemical energy of the explosive is transferred into the kinetic energy of the armature, and subseY quently into electrical energy. In extreme cases, the output of the FCG is limited by the kinetic energy available to transfer into electrical energy. 

As a practical matter, the assessment of the generator performance based on the efficiency of converting explosive energy into electrical energy is neither a desirY able viewpoint nor a useful way to design these devices. 

Helical Flux Compression Generator 

Thus far, we have mostly used the cylindrical generator as a model for our considY erations of FCG performance because of the geometrical simplicity of this style generator, cf. Fig. 2.1. However, the generator type that is of most interest generY ally is the spiral or helical flux compression generator, cf. Fig. 2.4. The reason is that the helical FCG may have a very large initial inductance, so the ideal gain from one of these units may be very large. Conceptually, a helical flux compresY sion generator is shown in Fig. 2.7 a.) before the explosive is initiated and in Fig. 2.7 b.) after the explosive has been detonated. The spiral winding of the stator provides inductance proportional to the number of turns squared. While there are several formulations for the inductance of a helical FCG, a very useable one is presented by Fowler [Fow75] as;

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