Magnetron Design Research Articles

High growth rate magnetron sputter epitaxy of GaN using a solid Ga target

High growth rate magnetron sputter epitaxy of GaN using a solid Ga target

Operation characteristics of a ten-cavity magnetron with TE11 mode extracted through compact diffraction output

We present the design of a ten-cavity magnetron extracting TE11 mode through compact diffraction output (DO). The effect of the DO length and the depth of the vane on the performance of the ten-cavity magnetron are investigated to design a compact diffraction structure. By adjusting the length of DO and the depth of the tapered cavities to provide a proper Qe, the output power and power conversion efficiency have been improved. Simulation results of the magnetron with compact DO (the length of the DO is about half an operation wavelength) show that the microwave power of 3.0 MW with a high conversion efficiency of 62% at 2.4 GHz is achieved under an applied voltage of 56 kV and a fixed axial magnetic field of 0.24 T. In addition, the length of the anode block is designed longer than the cathode to arrange the permanent magnet, which has been preliminary designed.

Effect of tilted closed-field magnetron design on the microstructure and mechanical properties of TiZrNbTaN coatings

A common design of sputtering systems is to integrate many magnetron sources in a tilted closed-field configuration, which can drastically affect the magnetic field in the chamber and thus plasma characteristics. To study this effect explicitly, multicomponent TiZrNbTaN coatings were deposited at room temperature using direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) with different substrate biases. The coatings were characterized by x-ray diffraction, scanning electron microscopy, nano-indentation, and energy dispersive x-ray spectroscopy. Magnetic field simulations revealed ten times higher magnetic field strengths at the substrate in single-magnetron configuration when compared to the closed-field. As a result, the substrate ion current increased ∼3 and 1.8 times for DCMS and HiPIMS, respectively. The film microstructure changed with the discharge type, in that DCMS coatings showed large sized columnar structures and HiPIMS coatings show globular nanosized structures with (111) orientation with a closed-field design. Coatings deposited from a single source showed dense columnar structures irrespective of the discharge type and developed (200) orientation only with HiPIMS. Coatings deposited with closed-field design by DCMS had low stress (0.8 to −1 GPa) and hardness in the range from 13 to 18 GPa. Use of HiPIMS resulted in higher stress (−3.6 to −4.3 GPa) and hardness (26–29 GPa). For coatings deposited with single source by DCMS, the stress (−0.15 to −3.7 GPa) and hardness were higher (18–26 GPa) than for coatings grown in the closed-field design. With HiPIMS and single source, the stress was in the range of −2.3 to −4.2 GPa with a ∼6% drop in the hardness (24–27 GPa).

Study on Flake Graphite Cathode Surface Microstructure in Relativistic Magnetrons

Flake graphite has excellent explosive electron emission performance for its plenty surface micro-bulges and high graphitization degree, but its advantages have rarely been studied in relativistic magnetrons. In this paper, flake graphite cathodes with different fineness were used in coaxial diodes and relativistic magnetrons, and the influence of the surface microstructure of the flake graphite cathode on the relativistic magnetron performance is demonstrated for the first time. The result showed that the graphite microstructure mainly affected the initiation stage of explosive emission. Moreover, the delay time is determined by the degree of graphitization and the surface microstructure of graphite, and the surface microstructure plays a major role. Under the applied voltage of ~330kV-~490kV, The finer flake graphite possessed a shorter emission delay and facilitated the microwave excitation. The excitation time of finer flake graphite is ~3ns, and ~5ns for lager flake graphite. After several operations of the relativistic magnetron, the edges of flake graphite were blunted, and the surface of the flake graphite appeared droplet-like areas formed by anode atom sputtering. This work reveals the advantages of the finer flake graphite cathode in the fast priming of the relativistic magnetron, thus shedding new light on cathode design of the relativistic magnetron.

Design and implementation of a X Band 9 GHz cavity magnetron for microwave applications

• A new type cavity magnetron design and implementation are performed. • Dual band characteristics has been observed around 10 GHz. • Double cavities in cathode and anode yield to different frequencies. • Power density of P = 108 W/m 2 has been achieved. Design and implementation of a new magnetron are performed. A comparison between standard cavity and anode/cathode cavities is examined. The magnetron has 8 cavities in anode and cathode. The operation frequency, radius, height, voltage and magnetic field density are calculated. The simulations are realized by finite element analysis. Eigen-frequencies, particle tracking and particle-in-cell analyses are studied. The proposed cathode cavity exhibits dual band characteristics in X-band (i.e. 9.108 GHz; 11.656 GHz) for specific excitation parameters. While the frequency of the D1 magnetron at 50 kV and 0.075 T is observed as 10.264 GHz, 9.1 GHz is obtained for D2 magnetron. In the experiments, maximum field and power densities are found as 129 V/m and 108.3 W/m 2 , respectively. The hallow cavity cathode gives an electron temperature 26.55 eV in the magnetized plasma media with an electron density 7.6 × 10 10 m −3 under 10 -5 mbar vacuum conditions.

Partly Semiconductor Covered Vane Fast Magnetron

Alterations in the structure of a magnetron, e.g., the A6 relativistic magnetron, are proposed, which considerably increase the device’s build-up speed. We cover the magnetron vane surfaces with semiconductor layers of nonzero electric conductivity, with an exact geometrical design. Semiconductor layers with considerable mechanical strength also provide excellent shielding for the vanes against the high-energy relativistic electrons’ bombardment. The novel structure introduces several new free parameters to the magnetron design procedure and considerably increases the design flexibility. A multistage exact optimization procedure, performed by extensive computer simulations, shows that applying silicon carbide layers with proper geometrical design doubles the build-up speed. In a general trend, we also indicate that adding semiconductor layers with nonzero electric conductivity to the magnetron vanes’ surfaces typically fastens the system by reducing the build-up transient time. It is verified that the insertion of conductivity to the vanes’ bodies with the proper design of shape and depth can increase the mode frequencies, build-up speed, and strength against electrons bombardment, saving the output amplitude. Finally, as shown by the simulation results data, the system behavior is analyzed theoretically.

A New Approach for High-Power Coaxial Magnetron Using Stacked Anode Resonators

A novel design of the ${X}$ -band megawatt-class coaxial magnetron using multiple-anode resonators placed in a stacked configuration is presented. The proposed design enhances the output power of a coaxial magnetron substantially without requiring external circuitry for power combining. The coaxial magnetron design is presented with two different cathode arrangements: one with separate cathodes and the other with connected cathodes. This article presents a new way for the generation of high-power microwaves by combining powers generated by multiple-anode resonators within a coaxial magnetron itself. The proposed coaxial magnetron is analyzed using the particle-in-cell (PIC) simulations. The output power of double-anode resonator magnetron is found to increase about 2.73 times compared with the coaxial magnetron with a single-anode resonator. The peak output power of 5.78 MW with 49.4% efficiency is obtained at 9.2906 GHz when a separate cathode arrangement is used, and both cathodes are excited simultaneously. The circuit efficiency and electronic efficiency are obtained as 83% and 59.5%, respectively. A wide frequency tuning range of 30.5 MHz is obtained, from 9.2840 to 9.3145 GHz. When only one cathode is excited, a different power level can be obtained. The output power can be enhanced further if more than two anode resonators are used in the connected cathode arrangement. The peak output power of 7.8 MW with 52% total efficiency is obtained with three anode resonators. The output performances of both the designs having different cathode arrangements are compared.

Magnetron High Power System Design

This paper describes the design of an X-Band Magnetron to Linear Accelerator (LINAC) High Power Transfer System consisting in an 8 resonant cavities Magnetron connected to a dedicated vacuum Dielectric Window (DW). A main analytical design of devices is shown with compact formulas and is followed by numerical optimization. Electromagnetic and Thermomechanical coupling between these devices is described, particular attention has been given to the Magnetron power coupling and DW matching. A Multiphysics modeling is proposed to consider thermal-structural effects due to the cathode heating for the Magnetron and the Joule effect for the DW. Thermal induced degradation of the device performances are estimated and proper materials and shapes are chosen in order to ensure the desired behavior of the system in operative conditions. The proposed study provided the evaluation of the Magnetron Working Points and DW Scattering parameters in Thermo-mechanical operative conditions. Technological strategies for device coupling are shown.

Machine Learning Investigation of the Rising Sun Magnetron Design and Operation

Many emerging applications of high-power microwave sources require operation at new and higher frequencies. Computer modeling is the main tool for the design and optimization of these sources, such as magnetrons. However, when designing a new source, the parameter space to scan can be too large to study with traditional techniques. We apply machine learning (ML) (supervised learning in particular) to search this parameter space automatically. We demonstrate this technique by optimizing the operation of a magnetron at 4 GHz, investigating selected parameters tradeoff and predicting operation space characteristics for the discovered device based on a limited amount of measurements. The combination of ML and optimization techniques that we demonstrate here has wide applicability for virtual prototyping and design of problems with sophisticated computer models and allows us to fundamentally reimagine the role of the human in the design workflow.

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.

Overview on recent progress in magnetron injection gun theory and design for high power gyrotrons

The magnetron injection gun (MIG) is one of the most critical subcomponents in gyrotrons. The electron beam, which has the primary role on the gyrotron operation, is generated and configured at this part of the tube. The electron beam properties determine the excitation mode in the cavity, the power of the generated microwaves and the gyrotron efficiency. The operation of MIGs could be influenced by several factors such as trapped electrons, manufacturing tolerances, roughness of the emitter ring, emitter temperature inhomogeneity, electron beam neutralization effect, etc. The influence of many of these factors on the electron beam quality has been systematically investigated during the last years. Several novelties have been proposed in order to limit the influence of these factors on the gyrotron operation. In particular, new design criteria have been proposed for the suppression of electron trapping mechanisms, a new type of the emitter ring has been proposed to minimize the influence of the manufacturing tolerances and edge effects on the beam quality, alternative MIG design approaches have been proposed, etc. An overview of all these works will be presented here.

Spatial-Harmonic Magnetrons with Cold Secondary-Emission Cathode: State-of-the-Art (Review)

Spatial-harmonic magnetrons with cold secondary-emission cathode are efficient high-power sources throughout the millimeter wavelength band. In this paper, resent advances in design, modeling, and fabrication of such magnetrons are described. Low-voltage magnetrons, sub-THz tubes, and magnetrons with metamaterial anode structure are described to illustrate these advances. The issue of the lifetime of the magnetrons with a cold secondary-emission cathode is also addressed. The main problems related with the usage of an auxiliary cathode in such tubes are considered and alternative solutions are discussed. Potentials for further improving the performance of spatial-harmonic magnetrons are analyzed as well.

Low-current cathode spatial harmonic magnetrons: analysis and realization based on metamaterial loaded slow wave structures

AbstractThis paper provides an overview of theory, design, simulation, and fabrication of novel spatial harmonic magnetrons (SHMs). An approximate analysis which provides the guidelines for the design and predicts the important characteristics of these devices will be presented. This analysis shows that the metamaterial loaded SHMs can start generating power with very small cathode current densities which is very important for designing THz sources based on SHMs. A design example with the operation frequency of 43 GHz together with the design procedure, PIC simulations, and measurement results will be examined.

Optical band engineering of metal-oxynitride based on tantalum oxide thin film fabricated via reactive gas-timing RF magnetron sputtering

Abstract In this paper, we demonstrate a novel technique, as called reactive gas-timing (RGT) RF magnetron sputtering, to control and design an optical band engineering of TaON thin films without an external heating substrate temperature and post annealing treatment process. The influence of the oxygen intervals ranged from 5 to 60 s on deposition rate, chemical composition and optical properties of TaON thin films were investigated. The chemical composition was characterized by auger electron spectroscopy (AES). The optical properties were determined by UV–Vis spectrophotometer and spectroscopic ellipsometry. The nitrogen atomic concentration of the TaON thin films deposited by RGT decreased when the oxygen gas-timing intervals increased. In addition, the RGT sputtered TaON films could be demonstrated band gaps engineering from 1.90 to 2.15 eV.

Factors determining the efficiency of magnetron sputtering. Optimization criteria

We report on the results of experimental study of the dependence of sputtering energy efficiency Kw in a dc planar magnetron sputtering setup on the discharge power, working gas pressure, magnetic field, cathode erosion depth, and the structure of the gas puffing system and anode. We propose that this parameter be used for comparing the degree of perfection of the magnetron design irrespective of the magnetron size and structural features. The results of measurements of Kw in sputtering of Al, Ti, Cr, Cu, Zn, Zr, Nb, Mo, Ag, In, Sn, Ta, W, Pt, and Au are considered. The optimization criterion is worked out for the magnetic system of the magnetron, which ensures the minimal working pressure and the maximal sputtering rate for the cathode. The results are analyzed theoretically.

Design of a Novel UWB Omnidirectional Antenna Using Particle Swarm Optimization

A UWB E-plane omnidirectional microwave antenna is designed and fabricated for IEEE 802.11a communication system and microwave magnetron source system as a radiation monitor. A cooptimization method based on particle swarm optimization (PSO) algorithm and FDTD software is presented. The presented PSO algorithm is useful in many industrial microwave applications, such as microwave magnetron design and other techniques with a high power level. The maximum measured relative bandwidth of 65% is achieved for the proposed antenna after a rapid and efficient optimization. Furthermore, the measured antenna polarization purity reaches about 20 dB at the communication C band. The PSO algorithm is a powerful candidate for microwave passive component design.

Tutorial on the Design of Hole-Slot-Type Cavity Magnetron Using CST Particle Studio

We present a simple design method for the hole-slot-type cavity magnetron. Our design model includes all principal parts of magnetron, namely, the cathode, the resonant system, the interaction space, and the magnetic circuit. We first find structural, electrical, and magnetic parameters using empirical formulas. Then, using empirical values as initial guesses, we build and simulate the 3-D model of magnetron in CST Particle Studio. In CST, we show that the eigenmode solver is essential for proper mode excitation; then, we use particle tracking and particle-in-cell simulations for the desired magnetron operation. For a fast convergent result, we study the impact of design parameters on the magnetron performance. We apply this design procedure to an X-band hole-slot-type magnetron with eight resonators. We believe that our method provides designers a simple, fast, and reliable tool for hole-slot-type magnetron design.

A High-Efficiency Megawatt-Class Nonrelativistic Magnetron

Numerical simulations of a prototype conventional magnetron capable of an RF output power exceeding 1.3 MW at peak efficiency greater than 87% for relatively low diode voltages of ~ 40 kV are presented. Virtual prototyping of the magnetron design is carried out on massively parallel architecture utilizing the 3-D improved concurrent electromagnetic particle-in-cell code. Simulations demonstrate that the magnetron is capable of stable and robust oscillations in the π mode at saturation with negligible mode competition at 912 MHz over a range of magnetic fields extending from B = 0.18 T to B = 0.275 T and voltages ranging from 37-56 kV. RF Output power ranged from 400 kW-1.5 MW over these voltages with efficiencies typically above 85%. Oscillations in the π mode follow the Buneman-Hartree resonance curve for all magnetic fields sampled with a window of π-mode oscillations typically extending over 6 kV. Electron back bombardment of the cathode as well as collisions with the slow wave structure acted as major loss mechanisms.

Design and Simulation of a Mega-Watt Class Nonrelativistic Magnetron

Numerical simulations of a prototype conventional magnetron capable of an RF output power exceeding 1.0 MW are presented. Magnetron design evaluation is carried out via numerical simulation using the 3-D Improved Concurrent Electromagnetic Particle-in-Cell code. The magnetron was capable of oscillating in the π mode with little mode competition at 655 MHz over a range of magnetic fields extending from B = 0.186 to B = 0.261 T and voltages ranging from 40 to 64 kV. RF Output power ranged from 400 kW to 2.1 MW over these voltages with efficiencies typically at 60%. RF power propagation upstream was identified as a major source of loss in the design.

마그네트론 구조의 열특성에 관한 해석

Magnetron is applied in microwave ovens for generating microwaves. It is composed of r-fin, yoke, A/F seals, gasket base, filter box. The temperature is occurred highly, when magnetron operate in its systems. Therefore the thermal characteristics must be considered in the design of magnetron. Because of its geometric complex, it is difficult to analysis the thermal characteristics. In this paper, temperature analysis is performed for all components. The commercial software ANSYS is used to consider both conduction and convection. The analysis is carried out by adding each component. An experiment on the thermal characteristics is performed to verify the reliability for simulation.