Magnetron With Diffraction Output Research Articles

Preliminary Experimental Study on a Compact Relativistic Magnetron With Diffraction Output of TEM Mode

A compact relativistic magnetron with diffraction output (MDO) of TEM mode has been investigated experimentally by using the EPA-90 high-voltage electron accelerator. The purpose is to verify the diffraction output in low-order mode predicted by numerical simulations. The diagnostic results have indicated that the MDO with all cavity extraction realizes the TEM mode output. When the diode voltage is 480 kV and the axial magnetic field is 0.49 T, the MDO could generate a microwave at a frequency of 2.42 GHz, corresponding to 950-MW output power and 25.8% conversion efficiency. This work paths a way for MDO to realize the radiation with low-order mode.

Particle-In-Cell Simulations on Long Pulse Large Current Behavior of Magnetron With Diffraction Output

Relativistic magnetron is an important choice for high power microwave (HPM) source because it is relatively small compared with other HPM sources; in this respect, magnetron with diffraction output (MDO) is particularly attractive because its output port is already a horn. Previous experimental studies on MDO were conducted using a short pulse (~25 ns) SINUS-6 accelerator; here, we investigate the dynamical properties of an MDO under long pulse (~100 ns) and high monitored current (25–30 kA) conditions using a commercial particle-in-cell (PIC) code. The results show that MDO operation can be divided into two stages, and both are capable of HPM generation. At 450-kV applied voltage, the first stage happens between 0 and 35 ns when the transparent cathode rods emit electrons and they form spoke motion, and the dominant frequency is 4 GHz. The second stage happens after 35 ns, the spoke rotation in conventional magnetron region continues, but massive particles begin to flow toward the extended vanes region, and the dominant frequency is 2 GHz. If the applied voltage is higher, the stage transition happens sooner. Particle phase space plots show particle propagation toward the output port direction, which is a natural consequence of the pulsed power system and Lorentz force. Placing a cathode endcap on top of the cathode rods cannot stop the particles. The output power is well in the gigawatt (GW) realm and no pulse shortening is observed despite considerable particles are lost through contact with the anode wall in 100-ns pulse. The peak beam to microwave conversion efficiency is not as high as reported experimental value, but still a decent number close to 60%. Overall, the MDO is a suitable choice for certain applications that requires 100-ns pulse in GW range with high energy efficiency.

PIC simulations of a frequency agile multicavity relativistic magnetron using irregular ring metamaterials driven by a transparent cathode

The design of an agile 5° irregular ring metamaterial for a 24-cavity relativistic magnetron with diffraction output (MDO) using single-stepped cavities for frequency switching is presented. By inserting six pieces of 5° irregular ring metamaterials in place of the traditional 5° vanes of a slow wave structure, the operating frequency can be tuned. When U = 400 kV high voltage is applied, with an applied magnetic field B = 0.36 T, the operating mode can be switched from the TE41 mode with a frequency of 2.585 GHz to the TE31 mode with a frequency of 2.282 GHz. The 24-cavity anode block is an electromagnetic medium which can support the operating mode working under its cutoff frequency, and the insertion of the irregular ring metamaterials alters its dispersion relation. The results suggest a new technique to achieve frequency agility by changing the dispersion relation of the electromagnetic system using a metamaterial unit cell. This work seeks to design a compact high power microwave source for a narrowband directed microwave wave beam that is suitable for frequency agility.

A Rectangular Vane-Type Relativistic Magnetron With Diffraction Output

In this article, a GW-level and high-efficiency $S$ -band eight-cavity relativistic magnetron with diffraction output (MDO) is proposed. A rectangular profile vane-type anode block is adopted to increase the volume of resonators, which leads to a promising higher output power. In particle-in-cell (PIC) simulations, the proposed eight-cavity MDO generates 2.5 GW output power with a power conversion efficiency of 70% when the applied voltage is 460 kV and the axial magnetic field is 0.44 T. The operation mode, $\pi $ -mode, oscillates at 2.75 GHz. The proposed eight-cavity MDO generates an RF output power over 2 GW in a wide range of voltages and magnetic fields, which exhibits its reliable performance in $\pi $ -mode.

Review of the relativistic magnetron

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.

A “crab-like” 12-cavity relativistic magnetron with diffraction output driven by a transparent cathode

We present computer simulations of a “crablike” 12 resonator cavity relativistic magnetron with diffraction output (MDO) designed by doubling the number of cavities from our earlier 6 resonator cavity crablike MDO. This work aims to design a compact high-power narrowband microwave source with frequency switching capabilities. UNIPIC particle-in-cell computer simulations show that the crablike 12-cavity MDO with a transparent cathode radiates the TE11 mode with output power 1 GW and electronic efficiency as high as 41% when powered using a 400 kV voltage pulse and 0.41 T magnetic field. Computer simulations also demonstrate that the crablike 12-cavity MDO can radiate different modes, such as the TE21 mode, the TE31 mode, the TE41 mode, and the TE51 mode. The TE21 mode, in particular, can be radiated at three different frequencies, as low as 2.12 GHz, a median operating frequency of 2.4 GHz, and a higher operating frequency of 2.91 GHz, when different magnetic fields are used.

The Characteristics Research on A6 Relativistic Magnetron With Diffraction Output Operating in the Negative First Harmonic of $2\pi$ /3 Mode

The characteristics of A6 relativistic magnetron with diffraction output (MDO) operating in the negative first harmonic of $2\pi $ /3-mode are studied in detail by theory analysis and particle-in-cell (PIC) simulation. By comparison with the fundamental harmonic of $\pi $ -mode, it is found that the negative first harmonic of $2\pi $ /3-mode with lower phase velocity can be advantageous to improve the interaction efficiency, but its delay in the establishment is longer. Furthermore, the negative first harmonic of $2\pi $ /3-mode requires a larger axial magnetic field to satisfy the resonating condition under the same diode voltage. Therefore, the total power occupied by the MDO operating with the negative first harmonic of $2\pi $ /3-mode can be decreased in the same diode voltage condition. This can result in reduced RF power output. Employing a diode voltage of 400 kV in PIC simulation, the optimal magnetic field for the negative first harmonic of $2\pi $ /3-mode and the fundamental harmonic of $\pi $ -mode are 0.51 and 0.39 T, respectively. The conversion efficiency at the negative first harmonic of $2\pi $ /3-mode is improved by 16.2%, whereas the input dc power is decreased by 1.22 GW, and the output RF power decreases 0.23 GW. Meanwhile, the oscillation delays about 3–4 ns.

A “crab-like” A6 relativistic magnetron with diffraction output driven by a transparent cathode

We present the design of an A6 relativistic magnetron with diffraction output (MDO) which looks like a crab and we named it the “crab-like” A6 MDO. This article shows that the crab-like A6 MDO driven by a transparent cathode can radiate the TE11 mode with an output power of about 1 GW when an optimized applied voltage of U=440 kV and magnetic field of B=0.43 T are used. Its electronic efficiency, as obtained using UNIPIC particle-in-cell (PIC) simulations, can be as high as 44% in S-band. The UNIPIC PIC code used in simulations also demonstrates that the crab-like A6 MDO can radiate both two electron spokes in the TE21 mode with an operating frequency of 2.1 GHz and four electron spokes in the TE21 mode with an operating frequency of 2.5 GHz when different magnetic field amplitudes are used for an applied voltage of U=400 kV. This result suggests that this configuration is favorable for mode switching. This work seeks to design a compact high power microwave source for a narrowband directed microwave wave beam that is suitable for mode switching investigations.

Optimizing the Parameters of a 12-Cavity Rising-Sun Relativistic Magnetron With Single-Stepped Cavities for $\pi $ -Mode Operation

We investigated the use of single-stepped cavities instead of typical tapered cavities in an A6 magnetron with diffraction output (MDO) and a 12-cavity MDO through particle-in-cell (PIC) simulations using MAGIC [1] and UNIPIC [2] in our earlier publications [3] – [5] . The interaction space, where the charged particles interact with the induced RF waves, was increased by replacing tapered cavities with single-stepped cavities in a 12-cavity rising-sun relativistic magnetron with diffraction output (RMDO) that the electronic efficiency of $\pi $ -mode generation in a 12-cavity rising-sun RMDO with single-stepped cavities driven by a transparent cathode [6] with gigawatt output power level can be as high as 83% for $\alpha = 12.5^{\circ }$ , 79% for $\alpha = 17.5^{\circ }$ , and 82% for $\alpha = 18.2^{\circ }$ at $\beta = 32^{\circ }$ , where $\alpha $ is the angle between the inner wall and the $z$ -axis, and $\beta $ is the angle between the outer wall and the $z$ -axis. When $\alpha $ , the angle between the inner wall and the $z$ -axis, is changed, the depth of single-stepped cavities was changed. This would lead to the coupling between deep cavities and shallow cavities in the 12-cavity rising-sun MDO changing too, and which finally results in different frequencies of magnetron operation in the $\pi $ -mode. As we know, gigawatt nanosecond output power pulse is useful for the nanoradar system, and our PIC simulations found that when a 400-kV voltage pulse of 10-ns duration is applied to a 12-cavity rising-sun MDO driven by a transparent cathode or a solid cathode, the output power of the $\pi $ -mode can be as high as 1.5 GW. Without loss of generality, for $\alpha = 12.5^{\circ }$ and $\beta = 32^{\circ }$ , the peak efficiency of $\pi $ -mode generation in a 12-cavity rising-sun MDO with single-stepped cavities design is around 82% and occurs for voltage $V\sim 400$ kV ± 50 kV. This paper describes optimizing the parameters in a 12-cavity rising-sun RMDO for the desired $\pi $ -mode operation.

Efficient Magnetron With a Virtual Cathode

We use particle-in-cell (PIC) computer simulations to demonstrate high-efficiency operation of a magnetron with diffraction output (MDO) that uses a virtual cathode in the interaction space instead of a physical cathode. The cathode generating the electron beam is external to the MDO interaction space and, therefore, is immune from electron bombardment, pulse shortening, decreasing electron efficiency, and frequency shift attributed to expanding cathode plasma. Electronic efficiencies comparable to those achieved with the MDO with a transparent cathode have been achieved in the simulations.

Particle-in-cell based parameter study of 12-cavity, 12-cathode rising-sun relativistic magnetrons for improved performance

Particle-in-cell simulations are performed to analyze the efficiency, output power and leakage currents in a 12-Cavity, 12-Cathode rising-sun magnetron with diffraction output (MDO). The central goal is to conduct a parameter study of a rising-sun magnetron that comprehensively incorporates performance enhancing features such as transparent cathodes, axial extraction, the use of endcaps, and cathode extensions. Our optimum results demonstrate peak output power of about 2.1 GW, with efficiencies of ∼70% and low leakage currents at a magnetic field of 0.45 Tesla, a 400 kV bias with a single endcap, for a range of cathode extensions between 3 and 6 centimeters.

Operation Characteristics of a 12-Cavity Relativistic Magnetron When Considering Secondary and Backscattered Electrons’ Emission

The particle-in-cell (PIC) simulation of an A6 magnetron with diffraction output (MDO) in our earlier work shows the peak output power (especially the short power pulse with several nanoseconds duration) is lowered when electrons with high energy strike the anode block, which leads to the emission of secondary and backscattered electrons. In addition, the PIC simulation for a 12-cavity MDO also shows when secondary electron emission occurs, the boundary for neighboring modes becomes more complicated than before. Replacing tapered cavities by single-stepped cavities in a relativistic MDO increases the interaction space where the charged particles interact with the induced RF waves. The electronic efficiency of the A6 relativistic MDO as well as the 12-cavity MDO with single-stepped cavities driven by the transparent cathode can be over 70% with gigawatts output power level. And with single-stepped cavities, the distance between the cathode and the wall of relativistic MDO is increased such that the possibility for electrons with high energy striking on the wall is decreased, which results in less emission of secondary and backscattered electrons under the same applied voltage. The PIC simulation demonstrated that in the 12-cavity MDO with single-stepped cavities driven by the transparent cathode with 400-kV applied voltage, the electrons with above 500 eV from cathode under the crossed electromagnetic field can strike on the anode block of MDO, resulting in a secondary and backscattered electron current that can cause different modes to be prevalent or stop the designed mechanism from working. Especially when applied with short voltage pulse with 10-ns duration, the output power pulse is shorted with peak power lowered. The simulation results presented in this paper possibly provide references for multicavity resonator when considering mode selection or mode switching experiments.

Simulation of Secondary Electron and Backscattered Electron Emission in A6 Relativistic Magnetron Driven by Different Cathode

Prticle-in-cell (PIC) simulations demonstrated that, when the relativistic magnetron with diffraction output (MDO) is applied with a 410 kV voltage pulse, or when the relativistic magnetron with radial output is applied with a 350 kV voltage pulse, electrons emitted from the cathode with high energy will strike the anode block wall. The emitted secondary electrons and backscattered electrons affect the interaction between electrons and RF fields induced by the operating modes, which decreases the output power in the radial output relativistic magnetron by about 15% (10% for the axial output relativistic magnetron), decreases the anode current by about 5% (5% for the axial output relativistic magnetron), and leads to a decrease of electronic efficiency by 8% (6% for the axial output relativistic magnetron). The peak value of the current formed by secondary and backscattered current equals nearly half of the amplitude of the anode current, which may help the growth of parasitic modes when the applied magnetic field is near the critical magnetic field separating neighboring modes. Thus, mode competition becomes more serious.

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.

Experimental investigation of a relativistic magnetron with diffraction output on a repetitive short pulse generator

An experimental investigation of a relativistic Magnetron with Diffraction Output (MDO) on a short voltage pulse generator, which has maximum repetition rate of 100 Hz and plateau of 2.5 ns, is detailed in this paper. Compared to the conversional solid cathode, a direct Density Modulation Cathode is capable for desired microwave radiation. When applied voltage is 200 kV and axial magnetic field is ∼0.12 T, the MDO radiates 120 MW of microwave with 2.3 GHz of central frequency. Power conversion efficiency reaches 22%. Pulse duration is 3 ns. At repetition rates of 50 Hz and 100 Hz, output microwave powers range from 90 MW to 120 MW. Life time is up to 104 shots.

Experimental investigations on the relations between configurations and radiation patterns of a relativistic magnetron with diffraction output

The relations between configurations of a relativistic magnetron with diffraction output (MDO) and radiation patterns obtained by experimental investigations are presented in this paper. A fluorescent lamps array is used to snap microwave patterns radiated from an A6 type MDO. Experimental results are well in agreement with computer simulations. Conclusions obtained from experiments are that (1) when an MDO operates at 2π mode, with all cavities tapered onto the output port, the MDO can directly radiate TE01 mode. (2) TEn1 (n > 0, n is integer) modes can be radiated from a π mode operating MDO with 2n azimuthally symmetric cavities tapered onto the output port. (3) By inserting optimal transition sections into tapered cavities, a pure TE11 microwave can be obtained.

Frequency agile characteristics of a dielectric filled relativistic magnetron with diffraction output

This paper reports the investigations of a dielectric filled relativistic magnetron with diffraction output (MDO) on frequency agile. The mechanism of frequency agile is theoretically analyzed. Particle-in-cell simulations and preliminary experiments prove the analytics. In experiments, under the working conditions, 605 kV and 0.3 T, a microwave with 1.98 GHz, 200 MW is radiated from an A6 type MDO when the 95% Al2O3 ceramics with the total thickness of 0.9 cm are filled. Compared with the microwave of 3.72 GHz, 240 MW obtained without the ceramics filled, the frequency agile from S band to L band is achieved.

Experimental investigations of the TE11 mode radiation from a relativistic magnetron with diffraction output

Directly radiating microwaves at TE11 mode, a relativistic magnetron with diffraction output (MDO) is experimentally investigated. Two important factors, transition section and working condition, significantly affecting the microwave powers, efficiencies, and pulse durations are analyzed. The experimental results on our designed MDO show that the optimized transition section with the parameters, 46 mm in height and 70 mm in length, is beneficial for producing high power TE11 mode microwaves. Under the low applied voltage condition (less than 650 kV), the power conversion efficiency will be higher than that obtained from the high applied voltage condition. ∼24 ns of the microwave duration is a typical value under the voltage duration of 56 ns. Pulse shortens will happen if the applied voltage is higher than 650 kV. When the applied voltage reaches 880 kV, the microwave duration is only just ∼12 ns. Impendence mismatch between the accelerator and the diode is the chief reason causing the pulse shortens.

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 TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> 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.

Investigation on the power combination of the relativistic magnetrons with axial extraction

The relativistic magnetron with axial extraction, also known as magnetron with diffraction output (MDO), is an important device for the miniaturization and compaetification of magnetron. It is also promising to be one of the most compact narrow band high power microwave sources. Based on the manners and traits of the MDO directly radiating the quasi-TE11 mode in axial direction, the investigation of the power combination of double MDOs with a horn antenna is carried out. After discussing the combination ways and results, a modified configuration is proposed for improving the radiation directivity. Finally, the results show that when the adjacent double MDOs have an open angle of 7 and the common horn antenna has the parameters of h = 600 mm and r = 340 mm, the mode reflection coefficient of the power combination system is 0.31, the maximum gain is 21.5 dB, the radiation mode is TE11.