Coaxial Cavity Research Articles

Beam dynamics optimization design of Rhodotron electron accelerator based on genetic algorithm and sensitivity analysis

The beam dynamics optimization study of Rhodotron electron accelerator for irradiation sterilization is introduced in this paper. The Rhodotron accelerator acceleration principle and the RF field distribution in the coaxial resonant cavity are described in detail. Beam dynamics in the Rhodotron accelerator are analyzed from both transverse and longitudinal directions. Beam dynamics of two kinds of Rhodotron electron accelerators with maximum beam energy of 10 MeV and 40 MeV were optimized based on multi-objective genetic algorithm. The key parameters of Rhodotron accelerators are determined, and the influence of some parameters on the overall acceleration effect is quantitatively analyzed. This paper provides some references for the research, manufacture, installation, and commissioning of this type of accelerator.

Dielectric properties of low moisture foods measured by open-ended coaxial probe and cavity perturbation technique

Dielectric properties of low moisture foods measured by open-ended coaxial probe and cavity perturbation technique

Theoretical Design of a Dual-Band TE01/TE02 Mode Gyrotron Traveling Wave Tube

A dual-band (K/Ka) TE01/TE02 mode gyrotron traveling wave tube is presented in this article. To suppress parasitic oscillations, a lossy-dielectric-loaded interaction circuit is employed. The particle-in-cell simulation results show that when it operates in K-band, the operating mode is the TE01 mode, with a peak output power of 87.1 kW, a saturated gain of 42.74 dB, and a −3 dB bandwidth of 0.7 GHz, and when it operates in Ka-band, the operating mode is the TE02 mode, with a peak output power of 62 kW, a saturated gain of 60.76 dB, and a −3 dB bandwidth of 2 GHz. Moreover, in the operating frequency range of the Ka-band, the overall gain is greater than 57 dB. To meet the requirements of dual-band operating, a dual-state magnetic injection gun is designed, a dual-mode coaxial cavity input coupler is proposed, and a dual-band output system is developed. All of these components showed excellent performance in simulations.

Simulation study for efficiency optimization of multi-beam klystron output cavity

Increasing klystron tubes’ efficiency is essential in developing new-generation colliders and free-electron lasers. Different factors can affect the efficiency of a multi-beam klystron. One of the significant factors is the electric field symmetry inside cavities, especially in the output section. In this research, two different types of couplers are investigated in the extraction cavity of a 40-beam klystron. The first approach is a single slot coupler, which is frequently utilized and easier to fabricate but disturbs the electric field symmetry inside the extraction cavity. The second method has a more complex structure with symmetric electric fields. In this design, the coupler consists of 28 mini slots on the inner wall of the coaxial extraction cavity. Both designs are evaluated via particle in cell simulations, and the results exhibit around 30% more power extracted from the structure with a symmetric field distribution. The symmetric structures can also decrease the number of back-streamed particles by up to 70%.

Theoretical designs and experiments on dual-band input coupler for gyrotron traveling wave tube

In this paper, a novel K/Ka dual-band input coupler for the gyrotron traveling wave tube is theoretically and experimentally investigated. This input coupler mainly consists of three modules, a Y-type power division coupler, a coaxial cavity coupler, and a Bragg reflector. When the dual-band coupler operates in K-band, the Y-type coupler couples out the TE11 mode, and simulation results show the −1 dB bandwidth is 3.3 GHz in the frequency range of 17.9–21.2 GHz. In Ka-band, the TE21 mode coupled out by the coaxial cavity coupler, the −1 dB bandwidth is 3.5 GHz within 33.7–37.2 GHz, and the reflection coefficient keeps a pretty low level. The prototype was fabricated and measured to further verify the designed dual-band input coupler's performance. The back-to-back cold test results show that the −3 dB bandwidth of the K-band is about 2.5 GHz, and the −3 dB bandwidth of the Ka-band is 2.44 GHz.

Yield surface for void growth and coalescence of porous anisotropic materials under axisymmetric loading

Ductile fracture in metallic alloys occurs by growth and coalescence of cavities. Growth, also referred to as homogeneous yielding, refers to rather diffuse plasticity around cavities, while coalescence, also termed as inhomogenous yielding, corresponds to the localization of plasticity along some planes or directions. Coalescence can develop in various patterns; three coalescence modes have been observed experimentally: internal necking, coalescence in columns and void sheeting. Plastic anisotropy of the material is known to have a significant effect on both homogeneous and inhomogeneous yielding. Therefore, in the present study, yield criteria accounting for the transition from homogeneous yielding to inhomogeneous yielding modes in anisotropic porous materials are obtained using kinematic limit analysis on a cylindrical unit-cell with a coaxial cylindrical cavity. Two types of plastic anisotropy are considered: Hill (1948) plasticity and crystal plasticity. The proposed analytical yield criteria are compared to numerical limit analysis computations and are found to qualitatively agree with simulations. In particular, plastic anisotropy, void shape effects and their coupling are well captured, especially regarding yield stresses and deformation modes. Finally, an homogenized model for Hill porous materials is obtained by supplementing evolution laws for microstructural parameters (void aspect ratio and ligament size ratios) derived from sequential limit analysis. Proposed evolution laws are then discussed in the light of numerical results and experimental evidence.

Parametric Model for Coaxial Cavity Filter with Combined KCCA and MLSSVR

Aiming at the problems of poor data effectiveness, low modeling accuracy, and weak generalization in the tuning process of microwave cavity filters, a parametric model for coaxial cavity filter using kernel canonical correlation analysis (KCCA) and multioutput least squares support vector regression (MLSSVR) is proposed in this study. First, the low-dimensional tuning data is mapped to the high-dimensional feature space by kernel canonical correlation analysis, and the nonlinear feature vectors are fused by the kernel function; second, the multioutput least squares support vector regression algorithm is used for parametric modeling to solve the problems of low accuracy and poor prediction performance; third, the support vector of the parameter model is optimized by the differential evolution whale algorithm (DWA) to improve the convergence and generalization ability of the model in actual tuning. Finally, the tuning experiments of two cavity filters with different topologies are carried out. The experimental results show that the proposed method has an obvious improvement in generalization performance and prediction accuracy compared with the traditional methods.

Intra-Cavity Cascaded Pumped 946/1030 nm Dual-Wavelength Vortex Laser Using a Spot-Defect Mirror

Due to their unique properties, vortex lasers have high application value in frontier fields such as optical micromanipulation, super-resolution imaging, quantum entanglement, and optical communication. In this study, we demonstrated a 946/1030 nm Laguerre-Gaussian (LG01) mode dual-wavelength vortex laser by using an intracavity cascade pumped structure and a spot-defect output mirror. Using a coaxial linear cavity structure, the 808 nm laser diode (LD) was used to end-pump the Nd:YAG crystal to generate a 946 nm laser and then use it to directly pump the Yb:YAG crystal in the cavity to generate a 1030 nm laser, and finally a 946/1030 nm dual-wavelength laser came out. By making a spot defect in the center of the output mirror to suppress the oscillation of the fundamental Gaussian mode laser and carefully adjusting the position of the laser crystals, the LG01 mode dual-wavelength vortex laser was output in single handedness. When the pump power was 40 W, the total output was 664 mW (356 and 308 mW at 946 and 1030 nm LG01 mode vortex lasers), and the total optical-optical conversion efficiency was 1.7%; the output power fluctuations of 946 and 1030 nm LG01 mode vortex lasers within 1 h were 3.43% and 3.13%, respectively; the beam quality factors M2 of 946 and 1030 nm LG01 mode vortex lasers were 2.35 and 2.40, respectively. It was proved that the generated dual-wavelength vortex laser had the wavefront phase expiϕ by the self-interference method.

Permittivity measurements for roasted ground coffee versus temperature, bulk density, and moisture content

For a large variety of food products, the moisture content can be indirectly determined by measuring their dielectric properties. In the case of coffee, the permittivity knowledge can be applied to determine the moisture content indirectly or for online moisture meters in automatic control of coffee dryers. However, there is little data on the dielectric properties of roasted ground coffee near the 2.45 GHz ISM band. In this contribution, the permittivity was measured versus temperature, bulk density, and moisture content. A resonant technique based on a coaxial microwave cavity was employed to obtain the complex permittivity as a function of those magnitudes near the 2.45 GHz ISM band. In addition, the permittivity of the coffee particle kernel has been estimated from a complex refractive index mixture equation, thus calculating the permittivity of the coffee particle kernel from the permittivity values of the mixture air-coffee (ground coffee) at different bulk densities. The results showed that both dielectric constant and loss factor increase for increasing temperature, bulk density, and moisture content values. Furthermore, expressions fitting the experimental data were provided, thereby facilitating the estimation of the values throughout the studied temperature, bulk density, and moisture content ranges.

An Easy Method to Determine the Effective Conductivity of Carbon Fiber Composites Using a Wall Perturbation Approach

Carbon-fiber-reinforced plastics (CFRPs) are of increasing popularity in a wide range of applications, and microwave curing promises significant reduction in processing times. However, for the design of an efficient microwave curing system, the composites' effective material parameters must be known. This work presents a measurement system using a wall perturbation approach with a coaxial cavity to determine the effective conductivity of a CFRP along the fiber direction.

Three-dimensional modeling and simulation of RF cavity for a transmitter with bandwidth of 40–100 MHz at 100-kilowatt level

A 1.5 MW final power amplifier is to be developed for ion cyclotron resonance heating (ICRH) system for the China fusion engineering testing reactor (CFETR) project. First, the feasibility of driver power amplifier with input matching circuit and output resonator cavity and a newly developed tetrode was cross-verified through three-dimensional (3D) simulations and experiments. A single coaxial cavity in parallel with the tetrode covered the frequency range of 40 to 100 MHz at a 100-kilowatt level. In contrast to the previous method of deducing matching parameters using RF circuit and transmission line theory, the use of 3D transmitter simulations provided more accurate matching parameters of tuning components at different operating frequencies. A new phenomenon of high frequency oscillation between the short strip inductor and the shield cavity was found in the input simulation results, which was subsequently verified by experiments. Specific reasons for dividing the output into two parts of high and low frequency were found through output circuit simulations. One is that the length of short stub decreases with the increase of operating frequency, thus decreasing the frequency resolution if all frequencies were using low frequency port. The other is that the coupling capacitor increases sharply with the increase of frequency due to parasitic effect in the low output. Further, the simulation facilitated the study of parasitic effects on matching parameters caused by strip-inductance, inter electrode capacitances of tetrode, and RF cavity. Thus, facilitating the design of final power amplifier in the future. Finally, the amplifier installed with the new tetrode DB968 achieved the design objectives in the test experiment with 150 and 110 kW power outputs at 48 and 100 MHz, respectively.

Theoretical Verification of Single-Reflector Compact Antenna Test Range With High Aperture Usage

In the reflector-based compact antenna test range (CATR), the aperture usage is one of our most concerned problems. Higher aperture usage means that in a CATR with the same aperture reflector, a larger quiet zone (QZ) can be generated to measure a larger aperture antenna. In this work, we theoretically derive a method to design a single-reflector CATR with high aperture usage. Specifically, the radiation function of the ideal feed for the offset-fed CATR is deduced. An offset-fed parabolic reflector CATR with this ideal feed can generate a QZ with 100% aperture usage analyzed by geometrical optics (GO). An offset-fed CATR with a 3 m side-length rectangular aperture parabolic reflector is designed and simulated by physical optics (PO) and physical theory of diffraction (PTD) in GRASP10. With the proposed feed, the aperture efficiency can reach about 74% at 100 GHz and over 86% from 200 to 500 GHz. The simulation results of the QZ field distribution in the system with an ideal feed and a manufactured coaxial cavity horn feed are presented and analyzed. Besides, we also summarize amplitude ripple, phase ripple, and cross-polarization isolation in the QZ to illustrate the performance of the single-reflector CATR.

Miniaturized Quad-Band Filter Design Using Substrate Integrated Coaxial Cavity

We propose a miniaturized quad-band filter (QBF), designed using substrate-integrated coaxial cavities (SICCs). The employed SICC structure consists of two vertically stacked substrates with a large circular patch embedded in between. The embedded patch is segmented unevenly into four pieces, which are shorted to the cavity's bottom wall through one or two blind vias. This SICC structure exhibits four independently controlled resonances with frequencies much lower than the frequency of its conventional SIW cavity counterpart, thus achieving size reduction. A sample quad-band filter is designed and fabricated for experimental measurement. Reasonably good agreement between measured and simulated data is observed.

Microwave Cavity Sensor for Measurements of Air Humidity under Reduced Pressure.

A high-sensitivity sensor for measuring moisture content in the air or air humidity under low pressure was designed on the basis of a half-wave coaxial microwave cavity. The method of measuring small variations in the signal phase at a cavity excitation frequency of 1.63 GHz was applied to detect low densities of water vapor. It allows the detection of variations in dielectric air permittivity in the seventh decimal place. A prototype of the sensor was tested in a vacuum chamber. It was calibrated by comparing the test results with the readings of a commercial pressure gauge and using the independent method of measuring the moisture content in rarefied air on the basis of the absorption of millimeter waves in the local line of water vapor at 183 GHz. The developed sensor can be used in laboratory experiments and full-scale geophysical research in the atmosphere onboard various aircrafts.

Iodine electron cyclotron resonance plasma source for electric propulsion

With the rapid development of commercial space in recent years, the low-power and low-cost propulsion systems are needed more and more urgently. Compared with conventional chemical propulsion, electric propulsion has a higher specific impulse. Compared with the conventional xenon propellant, iodine propellant that does not require high pressure storage, is cheap and close to the relative atomic mass and ionization energy of xenon. Electron cyclotron resonance source has the advantages of no internal electrode, low pressure ionization, high plasma density and compact structure, which is suitable for low power electric propulsion. Therefore, the study of low power iodine propellant electron cyclotron resonance plasma source is of great significance. In this study, a set of corrosion-resistant feed system with balanced and stable output of iodine vapor is designed. Then the iodine-corrosion-resistant electron cyclotron resonance thruster is designed completely. A corrosion-resistant coaxial cavity structure is used to feed the microwave to the thruster, and the channel magnetic field is changed into a cusped field to generate more electron cyclotron resonance (ECR) layers. Finally, the combined ignition experiment is successfully conducted, showing the first plasma source using electron cyclotron resonance to ionize iodine propellant that can be used for electric propulsion in the world. The analyses of experiments, static magnetic field, microwave electric field distribution show that the unstable plasma plume scintillation at low power and low flow is caused by the conversion between ordinary wave electron plasmon resonance heating mode and extraordinary wave electron cyclotron resonance heating mode. The decrease of ionization rate at a high flow rate is caused by electron loss, wall loss and electronegativity of iodine propellant. Based on this principle, an improvement scheme is proposed. The plasma source has no obvious damage after discharge, which indicates that it has the potential of long life. This work preliminarily proves that the low power electron cyclotron resonance electric propulsion scheme of low power iodine propellant is feasible.

Monolithically Integrated Coaxial Resonator-Based Filtennas Using SLA Three-Dimensional Printing

This letter reports on a new class of highly-miniaturized coaxial-resonator-based filtennas alongside a monolithic integration concept using digital additive manufacturing. The filtenna approach is based on the co-design of a coaxial cavity resonator and an annular slot antenna that collectively perform as a radiating resonating node within a coupled-resonator-based bandpass filter. Beam direction can be controlled by altering the position of the radiating slot. A stereolithography apparatus (SLA) monolithic integration concept is proposed for size compactness and reduced weight. For proof-of-concept validation purposes, first-, second-, and third-order filtennas were analyzed through electromagnetic simulations. Experimental validation was performed through the manufacturing and testing of a second-order top-slot filtenna, a second-order and a third-order side-slot filtenna with the following characteristics: center frequency: 4.75 GHz, 4.8 GHz and 4.6 GHz, fractional bandwidth: 7.4%, 8.3%, and 7.6% and realized gain: 5.5 dBi, 2.6 dBi, and 2.6 dBi.

Verification of the shaped beam feed for high aperture usage efficiency single offset parabolic reflector compact antenna test range

AbstractIn this letter, to verify that the shaped beam feed can enhance the aperture usage efficiency of a single‐offset parabolic reflector compact antenna test range (CATR), a shaped beam horn is proposed. First, we obtain the radiation intensity function of the feed. Then, a coaxial cavity horn feed with a half‐ring is designed to shape the illumination that reaches the main reflector. Measured results demonstrate that, with no edge treatment, the quiet zone size can be up to 75% of the main reflector diameter under 1.20 dB amplitude variations and 12° phase variations at 102.40 GHz, and 70% aperture usage efficiency ranging from 102 to 103 GHz with phase variations less than 12° and amplitude variations less than 1.40 dB. The design verifies that the shaped beam feed can enhance the aperture usage efficiency of a single‐offset CATR.

Design of a novel compact highly selective wideband bandstop RF filter using dual path lossy resonator for next generation applications.

This article presents the design of a wideband bandstop RF filter intending to improve selectivity and compactness. Conventional bandstop filter topology with finite unloaded quality factor produces degraded bandstop filter performance due to dissipation loss. In the proposed filter design, a novel dual path Capacitive Coupled Step Impedance Resonator (CCSIR) structure is used to obtain an infinite stopband attenuation. A uniform impedance resonator is used in Path 1, whereas Path 2 contains a resonator that is twice coupled to the transmission lines. The electrical length of both paths is chosen to be out of phase, resulting in a high rejection level at higher frequencies. It has been analyzed that the selectivity can be improved by increasing the order of the dual coupled step impedance resonator. The proposed design produces a wideband BSF centered at 5.25 GHz with a high rejection level of 104.3 dB and fractional bandwidth of 58.5%. The results have demonstrated that the resonant frequencies are regulated by varying the electrical length of CCSIR. Moreover, it has been realized that out of phase signal cancellation due to the dual path is involved in producing the finite frequency transmission poles, which further enhances the filter selectivity. However, the same electrical performance can only be achieved from coaxial cavities and waveguides due to the high-quality factor. The proposed topology is fabricated and measured on a high-frequency microstrip substrate having a low-quality factor with a compact output and better electrical performance compared to coaxial cavities or waveguides. Due to its high electrical performance and small size, the proposed BSF is appropriate for 4G and 5G (FR1) applications. The measurement shows good concurrence with the full-wave EM simulated results. The fabricated prototype of third order BSF has a compact size of (0.7 × 0.77)λg at 5.25 GHz.

Short-Length, High-Efficiency S-Band Coaxial Cavity Relativistic Multibeam Klystron Amplifier for Potential High Power Microwave Application

This letter reports the successful development of an S-band short-length, high-efficiency, coaxial cavity multi-beam relativistic klystron amplifier (CCMB-RKA). The simulation in one-dimensional genetic algorithm, capable of giving high-efficiency parameters, predicted 67% efficiency of CCMB-RKA, taking the interaction length as 600 mm, beam voltage as 420 kV, and beam current as 230 A. However, for accurate results, the CCMB-RKA was simulated again using three-dimensional code CHIPIC, taking RF input power, beam voltage, and beam current as 4.4 kW, 420 kV, and 3.22 kA ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$= {14} \times {230}$ </tex-math></inline-formula> A, 14 being the beam number), respectively, predicting the output power, gain, and efficiency of the device as 810 MW, 53 dB, and 60%, respectively. Finally, the designed CCMB-RKA was built and experimented with. Through 20 groups of the comparative experiments, the GW-level RF output power of the device, typically, 1.027 GW (peak), 60 ns pulse was demonstrated with 55% efficiency, 370 phase jitter, and 53 dB gain, taking the RF input power, beam voltage, and beam current as 4.8 kW, 453 kV, and 4.1 kA, respectively. The results establish the potential of the CCMB-RKA developed for high-power microwave applications.

Measurement of complex permittivity of liquids in the frequency range 100-1000MHz by using a re-entrant cavity.

For many liquid materials and biological media, their complex permittivity varies with frequency in the P-band (100-1000MHz). In this paper, a re-entrant coaxial cavity resonance test system with intensive multi-frequency points testing capability is designed for the P-band to realize the test of the complex permittivity of P-band materials. For this system, a test algorithm has been written, and on the basis of this system, a perturbation block has been designed, using stepper motors to control the up and down movement of the perturbation block to achieve frequency tunability of the cavity, enabling more P-band frequency test data to be obtained. The experimental results show that the system is suitable for testing the electrical parameters of P-band biological media and liquid materials and for testing solid materials in aerospace, electromagnetic shielding, and other fields where there is a great demand for P-band testing.