Input coupler for Ka band TE021 circular electric mode operation in a gyroklystron amplifier

An input coupler for the TE₀₂₁ circular electric mode in a gyroklystron amplifier through using TE₈₁₁ as a transition coupling mode in a coaxial cavity has been proposed and numerically simulated in a frequency range of Ka-Band with HFSS code. The coupling efficiency of the TE₀₂₁ mode and the suppression for the TE₈₁₁ mode in the main cylindrical cavity are deliberately considered by adjusting the position and size of coupling holes as well as the radius of the drift tubes. The numerical results show that the TE₀₂₁ mode can successfully be excited, and rational coupling efficiency and high mode purity for the TE₀₂₁ mode in the cylindrical cavity can be reached for the engineering application of gyroklystron amplifier study.     

激光脉冲驱动下双腔耦合系统的动力学特性

在外加激光控制下,研究了含有两能级量子比特的双腔耦合系统的动力学行为.基于系统的相互作用哈密顿量,得出了系统量子态激发概率的解析解.通过数值模拟讨论了3种特定情况下系统的动力学特性:外加脉冲与腔场发生近共振、比特与腔模大失谐条件下,腔模的最大激发概率小于0.07,腔模处于非激发状态,比特的激发概率出现瞬时衰减;比特与腔模强耦合条件下,腔模的激发概率近似0.5,腔模处于半激发状态,比特的激发概率出现高频振荡;腔场之间大跳跃条件下,腔模的最大激发概率小于0.07,腔模处于非激发状态,比特的激发概率出现高频振荡.     

Cold tests of A 10-GHz gyrotron cavity

Experiments have been conducted to characterize a gyrotron cavity designed to operate in theTE ₀₂₁ mode at 10 GHz. Cavity excitation was accomplished via a coupling hole introduced into the cavity wall and mode detection was carried out by means of two experimental arrangements. In the first, electromagnetic energy is coupled into a receiving waveguide through a small second hole drilled in the opposite side of the cavity. The other scheme uses a horn antenna to receive the power reradiated by the open resonator. Both schemes are discussed regarding mode detection, and measured data includes resonant frequency, loadedQ factor, axial electric field profile and farfield radiation pattern. Evaluation of the loadedQ factor is based on bandwidth measurements whereas standing-wave electric field profile is determined by using perturbation techniques. For severalTE modes, close agreeent between theory and experiment is found.     

Angular division multiplexer for fiber communication using graded-index rod lenses

An angular division multiplexer which uses graded-index (GRIN) rod lenses and a spatial modal filter (SMF) is described. Angular division multiplexing (ADM) uses selective excitation of mode groups " to multiplex signals in a transmission fiber. The GRIN-rod lenses collimate the input beams from two input fibers. The SMF selects particular mode groups from each input to be imaged on the transmission fiber. Design and construction of the device are described. Experimental results show that each signal is well confined to its designated mode groups. Crosstalk results are adequate for digital data transmission.     

A Single-Ridged Coaxial Hybrid TE011 Coupler with High Mode Purity

We design a single-ridged coaxial hybrid coupler which excites a TE₀₁₁ mode of high mode content in a cylindrical cavity, resonating at 28.2GHz. The coupler consists of a WR-28 rectangular waveguide, a coaxial TE_n11 cavity, and a cylindrical TE₀₁₁ cavity. Both TE₃₁₁ coaxial cavity and TE₄₁₁ single-ridged coaxial cavity are analyzed to examine the TE₀₁₁ mode purity in the central cavity. Mode purity analysis is performed by a field expansion method using Fourier-Bessel orthonormal basis functions. Numerical calculations predict that the TE₄₁₁ single-ridged coaxial cavity excites the TE₀₁₁ mode with mode purity of 98.6%, which is improved by 3% higher compared with the TE₃₁₁ coaxial cavity. Measurements on the single-ridged coaxial coupler show a resonant frequency at 28.078GHz and ohmic and external Qs of 1560, 473 respectively, which are in good agreement with the simulated results of a 3-D finite element electromagnetic code.     

Design and analysis of a coaxial coupler for a 35-GHz gyroklystronamplifier

A single rectangular TE₁₀ feed four-slot coaxial coupler is designed and built for excitation of a TE₀₁₁ cylindrical cavity mode for use in high-power millimeter-wavelength gyroklystron amplifiers. A high degree of mode purity is obtained and matching of the cavity to the input line is studied. A model based on the mode-matching technique and dipole radiators has been formulated to predict operation of this coupler. The resulting numerical code is capable of finding resonant frequency and cavity bandwidth in a small fraction of the time taken by more general finite-difference/finite-element design tools. The model can be extended to self-consistently include an electron beam, and the model is compared to a coupler design based on Hewlett-Packard's High-Frequency Structure Simulator code. The coupler has been successfully used in a high-power gyroklystron-amplifier experiment     

Analysis of a microwave power amplifier using a combiner/dividerwith circular cavities

Equations based on the discrete Fourier transformation developed for the analysis of a microwave power amplifier consisting of unit amplifiers and a power combiner/divider with circular cavities are presented. Equations of the mode voltages and currents of a power amplifier with some failed unit amplifiers are provided. The equations are obtained by taking into account the spurious-mode excitation to the cavity from the unit amplifiers, and are developed by using an analogous expansion by the discrete Fourier transformation (DFT). Equivalent circuits of the power amplifier for the various mode excitations are discussed, and load admittances for the spurious-mode excitations are applied to the equations for calculating the gain of the amplifier. The load admittance is analytically obtained using variational methods for a combiner with coaxial input/output ports. Numerical results for the power amplifier gain when there is a failed unit amplifier are shown. The effects of gain of the capability of suppressing spurious-mode waves using slits in the combiner are clarified     

CONCEPTUAL DESIGN STUDIES OF AN 84 GHz, 500 kW, CW GYROTRON

The feasibility of an 84 GHz, 500 kW, CW gyrotron for ECRH on an experimental tokamak will be presented in this paper. Mode competition and mode selection procedures are carefully investigated by considering various candidate modes and the TE_10,4 mode is chosen as the operating mode. A conventional cylindrical cavity resonator with weak input and output tapers and parabolic roundings is considered for interaction studies. Self-consistent, both single mode and time-dependent, calculations are carried out and power and efficiencies are computed for a typical set of beam parameters. The results show that an output power of well over 500 kW, CW and efficiency around 40% can be reached without a depressed collector.     

The Axially Modulated, Cusp-Injected, Slowly Varied Section Opened Cavity, Magnicon Amplifier

I introduce a novel hybrid microwave amplifier that utilizes the axial bunching mechanism of klystrons in conjunction with the energy extraction mechanism of cyclotron resonance masers on TM mode. A simpler analytic model is used to show the viability of the device configuration and to explore limitations of the scheme. An example of an 11.5 GHz, fourth harmonic amplifier is presented. Adopting a multi-particle in azimuth range of (0, π/2) whose divide thickness of beam into three share approach, numerical simulation are used to demonstrate bunching in physical space and to estimate system efficiency et al. It shall be shown that this configuration enables the design of eficient, high harmonic devices over a wide range of parameters. Magnicon [1]-[11] is a kind of microwave amplifier tabe, it operates on the mode of rotating E_n10 in cylindrical cavity and there is solid focus fine electrons beam. In it from theory, the paper researches the new type magnicon, it is changed into using annular electron beam and using slowly variable section opened cavity. Compared with magnicon, its pervence beams will may be increased, its frequency may be increased up to millimeter wave band, its bandwidth also will may be increased same times. Than model of new type magnicon is put forward. Starting from large signal's theory, interacting of the annular electron beam into driver cavity in between the mode of rotating E_n10, numerical value to simulate. It done on the small current density and small density of electron in space that electrons dynamic are simulated, which may uses Runge-Kutta method to do it.     

Optimization of bistable planar resonators operated near half theband gap

By using a modal approach that describes the optical response of a large class of nonlinear planar resonators under pulsed beam excitation we derive conditions to optimize the device with respect to different criteria. The influence of the nonlinearity is taken into account for both the cavity and the reflectors. The procedure results in simple algebraic formulas for the cavity thickness and the number of unit cells building the reflectors. The results hold likewise for microresonators of finite size and provide experimentalists with a useful tool to fabricate appropriate resonators for all optical switching operations     

Experimental Study of a High Power Coupler for a Tunable Cavity Formed by a Vane-Type Structure

In this study, a high power coupler designed for a tunable planar cavity is experimentally tested. The cavity consists of a periodical vane-type structure, of which the height of the vane can be mechanically adjusted so that the resonance frequency can be fine tuned. The cavity is designed to be operated at π mode and resonant at 2.45 GHz. The high power coupler is composed of a rectangular waveguide and a cylindrical ceramic rod with tapered ends. One end of the ceramic rod is intruded into the gap between two vanes of the cavity. Through this coupler, the TE₁₀ mode of the rectangular waveguide is converted into the TE₁₁ mode of the ceramic rod and then couples to the TEM mode in the gap between vanes of the cavity. Experimental results show that a microwave power up to 5 kW can be effectively transmitted to excite the π mode of the cavity . This cavity can be used to excite large area plasmas     

Computer Simulation of a 5.7GHz, 110kW Transit-Time Oscillator

A high-power transit-time oscillator producing 110kW at 5.7GHz in the TM₀₁₀ cavity mode is described. The device comprises a temperature-limited diode electron gun operating at 40A in the range from 28kV to 35kV and an intermediate coaxial cavity from which the microwave power is extracted through a TEM coaxial guide. The diode serves also as a resonant cavity, where electromagnetic oscillations are grown from noise. The effect of the applied voltage on both the output microwave power and the instability saturation time has been investigated leading to an optimal diode voltage of 33kV.     

Submilliwatt optical bistability in wafer fused vertical cavity at 1.55-/spl mu/m wavelength

We report on low-power optical bistability in a vertical cavity structure at 1.55-/spl mu/m wavelength due to the bandgap resonant dispersive optical nonlinearity of InGaAsP. In this structure, a GaAs-AlAs Bragg reflector grown on GaAs and the nonlinear medium grown on InP are bonded through wafer-fusion, leading to a high-quality vertical cavity after deposition of a top dielectric mirror. This device shows interesting characteristics for optical switching applications at fiber communication wavelengths, such as a switching contrast higher than 8:1 in the reflective mode and a bistability threshold power as low as 0.6 mW. True steady-state memory effect is observed with continuous-wave input, and the device switching time is in the ns range.     

Effects of circuit loss and space charge in gyro-travelling-wave tubes

A modified dispersion relation of a gyro-TWT using a cylindrical waveguide excited in aT E _mn -mode is derived incorporating the effect of the transverse space charge forces. The relation is subsequently studied considering the circuit losses and interpreted for the conventional TWT-type gain equation. The second harmonic operation using theT E ₀₂ cylindrical waveguide mode resonated with the second beam-harmonic mode is found to be more sensitive to the Pierce's loss and space-charge parameters for a gyro-TWT than the fundamental operation using theT E ₀₁ cylindrical waveguide mode resonated with the first beam-harmonic mode. It is established that these parameters substantially influence the device gain and must be considered for the prediction of its accurate value. Furthermore, these parameters when properly controlled can also improve the device bandwidth.     

Improving single-mode VCSEL performance by introducing a longmonolithic cavity

We report on the improvement of several selectively oxidized vertical-cavity surface emitting laser characteristics by introducing a long monolithic cavity. The samples compared are grown with various cavity lengths using solid-source MBE. The 980 nm-regime is chosen as emission wavelength to facilitate growth by using binary GaAs cavity spacers. A record high single-transverse mode output power of 5 mW at a series resistance of 98 Ω is obtained for a 7-μm aperture device with a 4-μm cavity spacer. Using an 8-μm cavity spacer, devices up to 16-μm aperture diameter emit 1.7 mW of single-mode power with a full-width at half-maximum far-field angle below 3.8°     

Linear and nonlinear analyses on gyropeniotron in a rectangular waveguide

The dispersion equation of the gyropeniotron using TE_n0 mode in a rectangular waveguide is derived in this paper. Through detailed numerical calculations of the dispersion equation using the TE₂₀ mode, dispersion curves of the peniotron are obtained. Some clear viewpoints are proposed here. In the nonlinear analysis, the model is assumed to be a rectangular cavity with two close ends, constant DC magnetic field and an axis-rotating electron beam. The analytical results of the peniotron using the TE₂₀₁ cavity mode assuming two operating conditions of ω = ω_c, and ω 3ω_c show 51% efficiency for to ω ω_c and 11% efficiency for ω3ω_c.     

Design of a Large Orbit Gyrotron with a Permanent Magnet System

The paper presents results of numerical analysis and outlines the computer-aided design of a novel high-harmonic gyrotron with a beam of electrons gyrating along axis-encircling trajectories. The electron beam is formed by a novel electron-optical system (EOS) based on an electron gun of diode type with thermionic cathode and gradual reversal of the magnetic field. The results of numerical simulations predict satisfactory performance of the EOS and appropriate beam quality parameters. The tube design allows one to install different cavities optimized for excitation of TE_4,1 mode at the fourth harmonic of the cyclotron frequency or TE_3,1 mode at the third one. The target parameters of the device are: frequency about 112 GHz; output power near 1 kW and efficiency of several percent.     

Numerical Simulation and Analysis of a New Type of Complex Cavity for Gyrotron Applications

A new type of complex cavity structure is used to improve the selectivity of modes in gyrotron resonant cavity with a rational position of inter-cavity wall and the shape of coupling holes between inter- and outer-cavities. The resonant characteristics of the complex cavity operating in TE₀₂₁/TE₀₃₁ mode at Ka frequency band are simulated and analyzed with Ansoft HFSS code, which shows that mode competition can effectively be alleviated with the cavity structure and it may be useful to the formation of clustered-cavity for extending interaction frequency bandwidth.     

Design and computer simulation of a gyrotwystron

We have designed a 4.5 GHz gyrotwystron consisting of an input cavity, a stagger tuned intermediate cavity and an output waveguide operating in the TE°₁₁, mode. Using a non-linear simulation code, we predict operation with a saturated gain of 22 dB, an efficiency of 22.5%, an output power of 60 kW and a bandwidth of ～2%. The efficiency and gain are similar to those achieved in a three-cavity gyroklystron operating at the same frequency, but the bandwidth is about an order of magnitude larger. Changing the profile of the B field optimizes efficiency and gain but decreases the bandwidth.     

INPUT COUPLER FOR Ka BAND TE021 CIRCULAR ELECTRIC MODE OPERATION IN A GYROKLYSTRON AMPLIFIER

An input coupler for the TE021 circular electric mode in a gyroklystron amplifier through using TEs11 as a transition coupling mode in a coaxial cavity has been proposed and numerically simulated in a frequency range of Ka-Band with HFSS code. The coupling efficiency of the TE021 mode and the suppression for the TE811 mode in the main cylindrical cavity are deliberately considered by adjusting the position and size of coupling holes as well as the radius of the drift tubes. The numerical results show that the TE021 mode can successfully be excited, and rational coupling efficiency and high mode purity for the TE021 mode in the cylindrical cavity can be reached for the engineering application of gyroklystron amplifier study.