Springer Theses Recognizing Outstanding Ph.D. Research Dimitry Mikitchuk Investigation of the Compression of Magnetized Plasma and Magnetic Flux Springer Theses Recognizing Outstanding Ph.D. Research Aims and Scope The series “Springer Theses” brings together a selection of the very best Ph.D. theses from around the world and across the physical sciences. Nominated and endorsed by two recognized specialists, each published volume has been selected for its scientific excellence and the high impact of its contents for the pertinent field of research. For greater accessibility to non-specialists, the published versions include an extended introduction, as well as a foreword by the student’s supervisor explaining the special relevance of the work for the field. As a whole, the series will provide a valuable resource both for newcomers to the research fields described, and for other scientists seeking detailed background information on special questions. 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More information about this series at http://www.springer.com/series/8790 Dimitry Mikitchuk Investigation of the Compression of Magnetized Plasma and Magnetic Flux Doctoral Thesis accepted by the Weizmann Institute of Science, Rehovot, Israel 123 Author Supervisor Dr. Dimitry Mikitchuk Prof. Yitzhak Maron Department of Physics of Complex Systems Faculty of Physics Weizmann Institute of Science Weizmann Institute of Science Rehovot, Israel Rehovot, Israel ISSN 2190-5053 ISSN 2190-5061 (electronic) Springer Theses ISBN 978-3-030-20854-7 ISBN 978-3-030-20855-4 (eBook) https://doi.org/10.1007/978-3-030-20855-4 © Springer Nature Switzerland AG 2019 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Supervisor’s Foreword It is my pleasure to introduce Dr. Dimitry Mikitchuk’s Ph.D. research for publi- cation in the Springer Thesis series. Dr. Mikitchuk was awarded his Ph.D. from the Weizmann Institute of Science in January 2017 for the research presented in this book. The main subject of his experimental study is the investigation of the compression of magnetized plasma and magnetic field by plasma implosion. This subject is relevant to the Magnetized Liner Inertial Fusion and likely to astro- physical plasmas, such as sunspots or other astrophysical objects where the mag- netic flux is frozen in an imploding plasma. Here, the magnetized plasma and magnetic flux compression are achieved by using a Z-pinch configuration with preembedded axial magnetic field. A pulsed axial current is driven through the plasma column generating an azimuthal magnetic field that through the Lorentz force compresses the magnetized plasma and the magnetic flux. The diagnostics of the magnetic fields are performed using a noninvasive spectroscopic technique based on the polarization properties of the Zeeman components of different atomic (or ionic) transitions, which enhances the sensitivity of the measurement. In his Ph.D. research, Dr. Mikitchuk made a highly important contribution to the understanding of the physics involved in magnetized plasma compression by the successful determination of the magnetic-field and current-density distributions in the non-equilibrium, transient plasmas. Specifically, his measurements include: (i) Development and implementation of localized magnetic-field spectroscopic diagnostics for pulsed-power systems based on the polarization properties of the Zeeman effect and using dopant species introduced by laser ablation. (ii) Direct measurement, for the first time, of the compressed axial magnetic field evolution and distribution during the implosion and stagnation in a Z-pinch with preembedded axial magnetic field utilizing noninvasive spectroscopic methods. (iii) Simultaneous measurement of the axial and azimuthal magnetic fields revealing unexpected results of the current distribution and the nature of the pressure balance of the axial and azimuthal fields. v vi Supervisor’s Foreword (iv) Investigation and demonstration of the mitigating effects of preembedded axial magnetic fields on magneto-Rayleigh-Taylor instabilities in Z-pinch implo- sions, using interferometric and imaging methods. These measurements are basic and essential for the advancement of the under- standing of complex plasma systems, both in laboratory and in nature. Since the magnetic field is a key factor in magneto-hydrodynamics modeling, the results are highly important for examining simulations, as well as for designing plasma con- figurations that are particularly relevant to the presently central Magnetized Liner Inertial Fusion approach. Rehovot, Israel Prof. Yitzhak Maron January 2019 Abstract In this research, I investigated fundamental phenomena occurring as magnetic-field flux and magnetized plasma are compressed by applied azimuthal magnetic fields. This subject is relevant to numerous studies in laboratory and space plasmas. Recently, it has gained particular interest due to the advances in producing plasmas of high temperature and density in experiments based on the approach of magne- tized plasma compression [1]. Many in the plasma physics community consider this approach to be the most promising for achieving controlled nuclear fusion. To advance this approach, it is essential to study experimentally the governing physical mechanisms that take place during the compression. Performing the required sys- tematic experiments is impractical in large-scale facilities designed for fusion demonstration. In our experiment, we employ a cylindrical (Z-pinch) configuration, in which a current (300 kA, rise time 1.6 ls) driven through a cylindrical plasma causes implosion of the plasma under the self-generated azimuthal magnetic fields (Bh). However, our cylindrical plasma is initially embedded in an axial magnetic field Bz. The field is quasi-statically applied prior to the high-current discharge, with a value of 0.4 T. Here, for the first time in these researches, Zeeman-splitting observations are used to measure the evolution and spatial distribution of Bz and Bh during the implosion and stagnation stages. The two fields are measured simultaneously, which is rather important due to the irreproducibility that characterizes such experiments of high-current pulses. The difficulties in these measurements are due to (1) the high electron densities in the plasma giving rise to large Stark broadening that smears out the Zeeman pattern, (2) the difficulty in distinguishing between Bz and Bh, and (3) the absence of light emission from the center of the plasma column. Indeed, in previous studies, under similar conditions, the B-fields were only indi- rectly estimated from the plasma radius. These challenges were achieved by employing a novel spectroscopic technique based on the polarization properties of Zeeman split emission, combined with a laser-generated doping technique that provided mm-scale spatial resolution. vii viii Abstract Systematic measurements were performed for different initial conditions of Bz and gas loads. The measurements showed that estimates of the B-fields based on the plasma radius are subjected to large errors and thus unreliable. Indeed, the simul- taneously measured Bz and Bh, together with the plasma radius and the discharge current, showed that the application of an initial Bz has