The cavity magnetron is the most compact, efficient source of high-power microwave (HPM) radiation. The imprint that the magnetron has had on the world is comparable to the invention of the nuclear bomb. High- and low-power magnetrons are used in many applications, such as radar systems, plasma generation for semiconductor processing, and—the most common—microwave ovens for personal and industrial use. Since the invention of the magnetron in 1921 by Hull, scientists and engineers have improved and optimized magnetron technology by altering the geometry, materials, and operating conditions, as well as by identifying applications. A major step in advancing magnetrons was the relativistic magnetron introduced by Bekefi and Orzechowski at MIT (USA, 1976), followed by the invention of the relativistic magnetron with diffraction output (MDO) by Kovalev and Fuks at the Institute of Applied Physics (Soviet Union, 1977). The performance of relativistic magnetrons did not advance significantly thereafter until researchers at the University of Michigan and University of New Mexico (UNM) independently introduced new priming techniques and new cathode topologies in the 2000s, and researchers in Japan identified a flaw in the original Soviet MDO design. Recently, the efficiency of the MDO has reached 92% with the introduction of a virtual cathode and magnetic mirror, proposed by Fuks and Schamiloglu at UNM (2018). This article presents a historical review of the progression of the magnetron from a device intended to operate as a high-voltage switch controlled by the magnetic field that Hull published in 1921, to the most compact and efficient HPM source in the twenty-first century.

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Laboratory. As an experimentalist, he understood my preferences for not coding and computer simulation, although he introduced me to CST and PIC simulator. After 6 months of polishing bits and bytes first results came out. Today, one year and 11 months later I do recognize the importance of computational tools. I would like to thank my committee members, Professors Mark Gilmore and Ahmed Elfrgani for joining Dr. Schamiloglu for their good advice and suggestions. I would like to acknowledge the financial support of the Electrical and Computer Engineering Department of the University of New Mexico and the Brazilian Government for providing me the necessary financial support throughout my thesis work. I especially would like to thank my advisor for the schollarship provided to support my studies. I am very much indebted to Mr. Bill Moeney, who provided deep conversation and thoughts about pulsed power regarding electron accelerators. v I am very much indebted to Dr Jane Lehr, who helped me in the modelling and simulaton of pulsed power systems and good conversations about high power electromagnetic fields. This thesis would not have been possible without the help, support, and patience of my lab mates Dmitrii Andreev (the Red October), Artem Kuskov (AK), Braulio Martinez, Stacie Hernandes, Joe, Raul, Bi, Jacob, Max, and the 5 new undergraduate students Chris, Eli, Cameron, Ethan, and Anna who drove me crazing with questions around the lab. It would have been a very lonely lab without all of them. I would like to thank staff members Mrs. Yvoné Nelson and Cornelia Platero who provided academic and administrative support for my thesis work.

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We report the successful operation of an advanced relativistic magnetron made up of separate anode segments and fed by a split cathode as suggested by Leopold et al. [Phys. Plasmas 27, 103102 (2020)]. A split cathode has the advantage that the emitter is placed outside the interaction region so that the cathode plasma does not cause pulse shortening. We find that the split cathode-fed magnetron performs as well as a common explosive emission plasma cathode but without the appearance of microwave pulse shortening during ∼200 ns while the pulsed generator is at its maximum power. The angular magnetron segments facilitate longitudinal slits in the magnetron's anode block, which allows for fast magnetic field penetration. This drastically decreases the power requirements of the pulsed generator feeding the axial insulating magnetic field producing solenoid and does not affect the operation of the magnetron. This results not only in a compact system but also in overall high electrical efficiency and the possibility to operate the relativistic magnetron in a repetitive mode.

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