Gigawatt Pulsed Power Technologies and Applications Patrik Appelgren Doctoral Thesis School of Electrical Engineering Space and Plasma Physics Royal Institute of Technology Stockholm, Sweden 2011 KTH School of Electrical Engineering Space and Plasma Physics TRITA-EE 2011:034 Royal Institute of Technology ISSN 1653-5146 SE-100 44 Stockholm ISBN 978-91-7415-962-2 Sweden Akademisk avhandling som med tillstånd av Kungl Tekniska Högskolan framlägges till offentlig granskning för avläggande av teknologie doktorsexamen i fysikalisk elektroteknik den 20:e maj 2011 kl. 10.00 i sal F3, Lindstedtsvägen 26, Kungliga Tekniska Högskolan, Stockholm. © Patrik Appelgren, maj 2011 Tryck: Universitetsservice US AB iii Gigawatt Pulsed Power Technologies and Applications Patrik Appelgren Abstract This thesis summarizes work on electrical pulsed power technologies and applications of very high electric power, of gigawatt levels, and involving high explosives. One pulsed power technology studied utilizes high explosives to generate electromagnetic energy while one application studied uses electromagnetic energy to disrupt fast-moving metal jets created using high explosives. The pulsed power source studied is a helical explosively driven magnetic flux compression generator. This kind of device converts the chemically stored energy in a high explosive into electromagnetic energy in the form of a powerful current pulse. Two generators were studied in order to investigate their performance and to understand their operation. An electrical circuit model was used to simulate the electrical behaviour and a hydrocode was used to simulate the explosion and mechanical deformation of the device. The experimental results obtained were peak currents of 269 kA and 436 kA corresponding to current amplification ratios of 47 and 39. The general shape of the measured and simulated current pulses was in good agreement and the simulated peak currents did not deviate more than 1 % from the measured peak currents. The other application studied is a protection technology against anti-tank warheads with shaped charges. A shaped charge is a device that creates a metal jet travelling at high velocity capable of penetrating several decimetres of steel armour. A powerful current pulse may be passed through the jet and due to iv heating and magnetic forces, the jet may be disrupted and its penetrative capability significantly reduced. A series of experiments has been performed to investigate the physical phenomena and a disruption process is suggested. Descriptors Magnetic Flux Compression, Explosives, Pulsed Power, Shaped Charges, Electric Armour, Circuit Simulations, Hydrodynamic simulations v Preface This work was carried out at the Swedish Defence Research Agency, FOI, Division of Defence & Security, Systems and Technology. Part of the work was performed within a research program on pulsed power technology for electromagnetic weapons, and part was performed within a research program on future armour protection. The work was funded by the Swedish Armed Forces. vi vii Acknowledgements First of all I would like to thank Gert Bjarnholt. He was the designer of the explosive flux compression generator and was managing the FOA (now FOI) project in this research area. Fortunately, for me, only one of the three generators manufactured was exploded. Two generators remained unused and during the last year before his retirement, Gert and I fired the two generators, covered with various measurement devices, very successfully. The second part of my doctoral work was research on electric armour, a novel technology for protection of military vehicles against shaped charge warheads. Thank you, Melker Skoglund - our work on electric armour would not have been such a success without your technical skills, innovative ideas and support. Thank you, Dr. Patrik Lundberg for your support, encouragement and technical expertise. I would like to thank Prof. Nils Brenning and Prof. Anders Larsson, my supervisors at KTH and FOI for their encouragement, support and help in analysing results and writing the papers. Thank you, Dr. Torgny Carlsson, FOI, for encouraging me to begin the PhD-studies, and for your support. A special thanks to you Dr. Bucur Novac, Loughborough University, UK, for your help with the modelling, the analysis of the experiments, and the interpretation of the results from the flux compression generator experiments. Thank you, Dr. Andreas Helte for setting up and performing the hydrodynamic simulations of the explosion process in the flux compression generator, providing valuable input to the electric armour research, and for guiding me into the area of detonics. Dr. Tomas Hurtig and Lars Westerling, it has always been a pleasure to discuss the complex physics observed in the experiments and in the output from your numerical calculations. Other colleagues at FOI that have been supportive and contributed to this work in different ways are Dr. Mose Akyuz, Mattias Elfsberg, Cecilia Möller and Sten Nyholm. My gratitude to the workshop and construction service at FOI Grindsjön for their assistance and help in manufacturing all the necessary auxiliary equipment required when performing these experiments. Finally I would like to thank Anna, my parents Berit and Åke, family and friends for their support, encouragement and patience. viii To Anna and my son Linus x 1 List of papers The work on explosively driven magnetic flux compression generators was thoroughly presented in the licentiate thesis 1. Patrik Appelgren, “Experiments with and modelling of explosively driven magnetic flux compression generators”, Licentiate thesis, TRITA-EE 2008:53, KTH, November 2008 This thesis is based on the work presented in the following journal and conference papers. On explosively driven magnetic flux compression generators: I. P. Appelgren, G. Bjarnholt, N. Brenning, M. Elfsberg, T. Hurtig, A. Larsson, B. M. Novac, and S. E. Nyholm, “Small Helical Magnetic Flux Compression Generators: Experiments and Analysis”, IEEE Transactions on Plasma Science, Vol. 36, No. 5, pp. 2673-2683, October 2008 II. P. Appelgren, N. Brenning, T. Hurtig, A. Larsson, B. M. Novac, and S. E. Nyholm. ”Modeling of a Small Helical Magnetic Flux Compression Generator”, IEEE Transactions on Plasma Science, Vol. 36, No. 5, pp. 2662-2672 , October 2008 III. P. Appelgren, A. Larsson and S. E. Nyholm, “Numerical Simulations of Flux Compression Generator Systems”, proceedings of the 20th IET Pulsed Power Symposium 17-19 September 2007, Oxfordshire, UK pp. 123-127 IV. B.M. Novac, M. Istenič, J. Luo, I.R. Smith, J. Brown, M. Hubbard, P. Appelgren, M. Elfsberg, T. Hurtig, C. Nylander, A. Larsson and S.E. Nyholm, “A 10 GW Pulsed Power Supply for HPM Sources”, IEEE Transactions on Plasma Science, Vol. 34, No. 5, pp. 1814 - 1821 , October 2006 2 On electric armour: V. Patrik Appelgren, Melker Skoglund, Patrik Lundberg, Lars Westerling, Anders Larsson, Tomas Hurtig, “Experimental Study of Electro- magnetic Effects on Solid Copper Jets”, Journal of Applied Mechanics, Vol. 77, No.1, pp. 011010-1 -- 011010-7, January 2010 VI. Patrik Appelgren, Torgny E. Carlsson, Andreas Helte, Tomas Hurtig, Anders Larsson, Patrik Lundberg, Melker Skoglund and Lars Westerling, ”Interaction between Solid Copper Jets and Powerful Electrical Current Pulses”, Journal of Applied Mechanics, Vol.78, No.2, pp. 021006-1 -- 021006-7, March 2011 VII. Patrik Appelgren, Melker Skoglund, Patrik Lundberg, Lars Westerling, Anders Larsson, Tomas Hurtig, ”Disruption Mechanisms in Electrified Solid Copper Jets”, Journal of Applied Mechanics, Vol.78, No.2, pp. 021014-1 -- 021014-5, March 2011 VIII. P. Appelgren, A. Larsson, P. Lundberg, M. Skoglund, L. Westerling, “Studies of Electrically-Exploded Conductors for Electric Armour Applications”, Acta Physica Polonica A, Vol. 115, No. 6, pp. 1072- 1074, 2009 IX. P. Appelgren, L. Westerling, M. Skoglund, P. Lundberg, T. Hurtig, A. Larsson, “Radial Jet Dispersion due to Current Interaction in an Electric Armour Application”, 24th International Symposium on Ballistics, New Orleans, LA, 22-26 September 2008 X. P. Senior, I. R. Smith, P. Appelgren, M. Elfsberg, P. Lundberg, M. Skoglund, “A 400kJ Mobile Pulsed Power System with Variable Pulse Forming”, Proceedings of Megagauss XI, pp 257-261, London, UK, 2006 My contributions to the included publications: Paper I-III: These papers present the experimental work with, and numerical simulations of, explosives driven flux compression generators. The generators were designed and constructed at FOA in 1994-1995. My contribution was to modify, plan and perform the experiments with two remaining generators and to adapt and implement a generator model, developed by Dr. Bucur Novac, into Matlab-Simulink and perform various simulations and parametric studies. I performed the analysis of the experimental data and simulation results and wrote the papers with the support by the co-authors. 3 Paper IV: This paper presents a 10 GW pulsed power supply designed to power a high power microwave (HPM) source. The system was developed by Loughborough University and in order to demonstrate the operation with a microwave source, FOI brought a vircator to Loughborough and mounted the systems together. My contribution was to adapt the FOI vircator to the 10 GW system, participate in the experiments and contribute in writing the paper. Paper V-VII: These papers present the experimental work, results and analysis performed to study the various phenomena occurring when a high velocity metal jet is electrified when passing