Review of the relativistic magnetron

Abstract

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.

Emission Uniformity of an Annular Graphite Cathode With a Focusing Electrode in a High Power Vacuum Diode

“…As high power microwave (HPM) sources have gradually matured for at least four decades [1]- [7], HPM technology entered widespread civilian and military use. An annular explosive emission cathode (EEC) is widely utilized in the HPM devices to generate an intense relativistic electron beam (IREB).…”

Experimental Testing of a 3-D-Printed Metamaterial Slow Wave Structure for High-Power Microwave Generation

“…printed SWSs fully in metal [5]. Due to the dimensions of the device that was ultimately selected, 3D printing in metal was not possible because of the wall thickness.…”

Highly efficient compact gigawatt‐level microwave source using relativistic electrons: radial relativistic magnetron

“…Among all, the relativistic magnetron (RM) is one of the most attractive high‐power microwave (HPM) sources, due to its compactness and high efficiency. Since the first RM is experimentally developed by Bekefi and Orzechowski at MIT in 1976 [9], lots of efforts have been made to improve the efficiency and the compactness [4]. A good review of magnetrons can be found in recent literature [4].…”

“…The term 'relativistic' refers to velocities closer to the speed of light where the electron beams with high voltage of hundreds of kV and high current of tens kA are used. The progress results from three main developments: conventional microwave devices such as klystrons [1], backward-wave oscillators [2,3] and magnetrons [4] with the use of higher currents and voltages; high current devices such as vircators [5] and magnetically insulated local oscillators without external magnetic field [6]; and fast-wave devices such as gyrotrons [7] and free-electron lasers [8] which can generate higher powers at higher frequencies than conventional devices making use of relativistic effects. Among all, the relativistic magnetron (RM) is one of the most attractive high-power microwave (HPM) sources, due to its compactness and high efficiency.…”

“…When the phase velocity decreases and the most effective π-mode is chosen in all the magnetrons, the circuit becomes highly dispersive leading to the mode competitions. To overcome the issue of the mode competition, various technical approaches such as cathode priming, magnetic priming and strapping have been successfully carried out for the stable operation (see [4]). However, there exists a continuing need to stabilise the magnetron interaction at the operating mode without sacrificing the compactness.…”