Mikhail I. Fuks

70% Efficient Relativistic Magnetron With Axial Extraction of Radiation Through a Horn Antenna

At the Nagaoka University of Technology (Japan), Daimon and Jiang used particle-in-cell (PIC) code simulations to demonstrate that the electronic efficiency of the A6 magnetron with axial extraction can be increased from 3% up to 37% applying different diffraction outputs, from tapered cavities in a conical horn antenna to modified expanded ones that improve magnetron matching with the antenna. This paper presents PIC code simulation results for the modified magnetron design using a transparent cathode, in contrast with Daimon and Jiangs simulations that used a solid explosive emission cathode. Furthermore, by further optimizing the magnetron parameters, we demonstrate an efficiency approaching 70% with gigawatt radiation power for an applied voltage of 400 kV. By maintaining a synchronous interaction of electrons with the operating wave, we found that the radiation power increases as the square of the diode voltage up to a diode voltage of 800 kV with short rise time that does not exceed 20 ns. In addition, we show that using a transparent cathode promotes avoiding the regime of hard excitation of magnetrons.

Mode conversion in a magnetron with axial extraction of radiation

We demonstrate the ability to form simple radiation patterns from a relativistic magnetron with axial extraction. This is achieved by tapering onto a conical antenna only those cavities of the anode block that correspond to the symmetry of the radiated modes. The efficiency of mode conversion of the operating pi-mode into a radiated mode using this method is demonstrated using computer simulations of a six-cavity magnetron

Pulsed power-driven high-power microwave sources

The advent of pulsed power technology in the 1960s has enabled the development of very high peak power sources of electromagnetic radiation in the microwave and millimeter wave bands of the electromagnetic spectrum. Such sources have applications in plasma physics, particle acceleration techniques, fusion energy research, high-power radars, and communications, to name just a few. This article describes recent ongoing activity in this field in both Russia and the United States. The overview of research in Russia focuses on high-power microwave (HPM) sources that are powered using SINUS accelerators, which were developed at the Institute of High Current Electronics. The overview of research in the United States focuses more broadly on recent accomplishments of a multidisciplinary university research initiative on HPM sources, which also involved close interactions with Department of Defense laboratories and industry. HPM sources described in this article have generated peak powers exceeding several gigawatts in pulse durations typically on the order of 100 ns in frequencies ranging from about 1 GHz to many tens of gigahertz.

rf mode switching in a relativistic magnetron with diffraction output

The relativistic magnetron with diffraction output (RMDO) has demonstrated nearly 70% efficiency in recent simulations. This letter reports a rapid mode switching technique in the RMDO using a low power, short-pulse, external single frequency signal. The MAGIC electromagnetic finite-difference-time-domain particle-in-cell code used in simulations demonstrated that an input signal of 300 kW is sufficient to switch neighboring modes in a gigawatt output power A6 RMDO with a transparent cathode, whereas for the original A6 magnetron configuration with radial extraction driven by a transparent cathode 30 MW is required. This frequency agility adds additional versatility to this high power microwave source.

An X-band gigawatt amplifier

In an X-band Cerenkov amplifier driven by a 0.8-MeV 6-kA electron beam, a gigawatt-level of power radiated in a Gaussian pattern in a 70-ns pulse duration has been demonstrated. The coherence of the output radiation is provided by dividing the oversized interaction space into separate sections with different azimuthal symmetry that couples only with the electron beam. A large gain of 47 dB and an efficiency of 23% are obtained using a regenerative amplification of a backward-wave amplifier (BWA) that produce a modulation of the electron beam. The efficiency of this device is 27% when the BWA-modulator operates in the regime of auto oscillations.

Optimization of the parameters of a relativistic magnetron with diffraction output

We consider a magnetron with diffraction output as the most natural variant of magnetrons for relativistic electron energies because of the unique combination of such favorable properties as high output power, compact design, high resistance to microwave breakdown, the ability to work with extremely high currents, and the possibility to form desirable output radiation patterns. This paper presents preliminary parameters for the design of such a high power microwave generator, and contrasts its features with magnetrons of the traditional design.

Compact Relativistic Magnetron With Gaussian Radiation Pattern

A compact A6 relativistic magnetron is proposed which operates in the π-mode and whose radiation is extracted axially as a TE11 mode through a cylindrical waveguide with the same cross section as that of the anode block. This radiated mode is similar to a Gaussian microwave beam. The advantages of this magnetron include the minimal volume of the applied magnetic field and, as a consequence, the proximity of the electron dump to the anode block for the electrons leaking from the interaction space that minimizes both the diameter and the axial length of the magnetron. By using MAGIC particle-in-cell (PIC) simulations, we demonstrate the possibility of generating a Gaussian radiation pattern with power of about 0.5 GW when the applied voltage is 350 kV. This compact magnetron is easier to implement than the magnetron with diffraction output (MDO), although with reduced efficiency.

Frequency Switching in a 12-Cavity Relativistic Magnetron With Axial Extraction of Radiation

The possibility of mode switching from one pulse to another in a 6-cavity gigawatt magnetron with axial extraction of radiation through a horn antenna (such a magnetron is known as the MDO, i.e., magnetron with diffraction output) using a weak (200-300 kW), short (15-ns), and single-frequency RF signal was demonstrated using particle-in-cell simulations in our earlier work. This mode switching exploits the symmetric nature of the MDO that facilitates the use of any eigenmode as the operating mode. All scenarios of mode switching were considered using common properties of dynamical systems with two stable states separated by an unstable saddle point. In this paper, we continue to study the problem of mode switching, but this time for a 12-cavity MDO, for which we found splitting of the radiation frequency for each eigenmode owing to its different longitudinal distributions. Since splitting manifests as a bifurcation of frequency for definite values of the applied axial magnetic field, scenarios of frequency switching for this 12-cavity magnetron are considered.

Selective multichannel feedback

A simple and effective method of mode selection in oversized electrodynamic systems is described. The method is based on forming a solitary resonant combination of eigenmodes by a system of Bragg reflectors having a different azimuthal symmetry at the ends of the electrodynamic system. Application of this method to a resonant traveling-wave tube is considered.

Operation Characteristics of 12-Cavity Relativistic Magnetron With Single-Stepped Cavities

The possibility of using single-stepped cavities to replace the common tapered cavities was studied using particle-in-cell simulations in an A6 magnetron with diffraction output (MDO). The replacing of the tapered cavities by the single-stepped cavities in a 12-cavity MDO increases the interaction space where the charged particles interact with the induced RF waves. The electronic efficiency of the 12-cavity MDO with single-stepped cavities driven by the transparent cathode [2] of GW output power level can be as high as 73% for α = 18.2°, 74% for α = 17.5°, and 72% for α = 12.5° at β = 32°, where α is the angle between the outer wall and z-axis, and β is the angle between the inner wall and z-axis. The depth of single-stepped cavities is changed when α is changed, which results in different frequency range of magnetron operating modes. When a 400-kV voltage pulse of 10-ns duration is applied to a transparent cathode or a solid cathode, the output power can be as high as 1 GW. Without loss of generality, for α = 12.5° at β = 32°, the peak efficiency around 70% of 12-cavity MDO with single-stepped cavities design occurs at the voltage (V ~ 400 ± 50 kV). The results presented in this paper provide references for relativistic magnetron mode selection or mode switching experiments when choosing the input parameters (magnetic field and accelerating voltage) allowing the magnetron to operate in the desired operation mode.