Design of a system converting an output radiation of frequency tunable gyrotron into a gaussian beam

A novel design of a versatile quasi-optical system for conversion of gyrotron radiation into collimated gaussian beams is presented and discussed. The proposed system consists of a quasi-optical antenna, two ellipsoidal mirrors and a spatial filter which truncates the sidelobe radiation. The system is appropriate as a transmission line for frequency tunable gyrotrons operating at TE_0n and TE_1n modes. As an illustration of our approach, we present results which demonstrate the applicability of the developed system for conversion of the radiation generated by the Gyrotron FU IVA. The examples include conversion of four TE_1n mode outputs (TE₁₂, 170 GHz; TE₁₃, 271 GHz; TE₁₄, 372 GHz; TE₁₅, 472 GHz) into gaussian-like beams and three TE_0n modes (TE₀₂, 223 GHz; TE₀₃, 323GHz; TE₀₄, 423 GHz) into bigaussian-like beams.     

Design of a quasi-optical system with variable output beam size

A quasi-optical system consisting of a quasi-optical antenna and two ellipsoidal mirrors can convert the gyrotron output (TE₁₅ mode, 354GHz) into a gaussian-like beam. The waist size of the beam produced is adjusted by moving a second ellipsoidal mirror. The second mirror with focal length of 520mm offers a tunable range from 2.0mm to 5.4mm, and those with focal lengths of 1190mm and 2390mm offer other tunable ranges from 5.1mm to 12.9mm and from 12.0mm to 25.1mm, respectively.     

Design of a quasi-optical mode conversion system with variable output beam size

The quasi-optical system consisting of a quasi-optical antenna and two parabolic mirrors can convert the TE₀₃ mode output (f = 301 GHz) of the Gyrotron FU IV into a well collimated, linearly polarized beam. This system offers the possibility of tuning the size of the beam produced from 5 mm up to 24 mm by rotating and moving the two parabolic mirrors.     

170 GHz回旋管准光模式变换器的设计

针对170 GHz回旋管研究,设计了一种高效Denisov准光模式变换器,该回旋管工作在模式。模式变换器由微扰结构的辐射器和镜面系统组成。基于耦合模理论和矢量绕射理论,研究了两级微扰辐射器,优化设计了镜面系统。仿真结果显示,模式转换为高斯光束,其输出功率转换效率为93.7%。     

Experimental study of a single-mode quasi-optical gyrotron

The first experimental results of a high-power quasi-optical gyrotron are presented. The cavity was designed to eliminate all mode competition, longitudinal as well as radial. Powers to 80 kW and efficiencies to 11% were measured with indications that the actual electronic efficiency was at least a factor of 1·5 greater.     

Cold tests of quasi-optical gyrotron resonators

Cold tests which have been performed on quasi-optical gyrotron resonators at frequencies near 94 and 120 GHz to measure cavity Q are discussed. The separation between the resonator mirrors was varied between 0.15 and 0.35 m. Quality factors ranging from 10000 to 100000 are shown. Good agreement is shown between the measured data and values calculated from scalar diffraction theory. The experimental effect of misaligning the mirrors is examined     

（英）140GHz回旋行波管放大器准光学注入结构的设计

作为140GHz共焦波导回旋行波管放大器设计中的一个创新部分,关于准光学注入结构的设计方法将详细论述.归因于高斯光束对频率扰动的欠敏感特性,这样的注入结构具有比传统波导插入耦合器更大的带宽.注入系统包括耦合天线、镜面变换器和波纹波导三个部分,最终在高于50%功率注入水平下达到6.8GHz的带宽,并克服了可能的寄生模式振荡和由加工误差导致的注入效率迅速下降的问题.     

MAGICTRAC,a novel method for conversion of whispering-gallery modes into a free-space Gaussian-like beam

A novel device, MAGICTRAC, is described for efficient conversion at millimeter wavelengths of the TE _m,n whispering-gallery mode into a linearly polarized, free-space Gaussian-like beam. MAGICTRAC uses a mode-converting waveguide taper and three mirror optics, one of which incorporates a twist reflector to linearly polarize the output beam. An example design is presented for the TE_15,2 mode at 140 GHz with a calculated efficiency of 96%. Related possible applications include (1) installation of the MAGICTRAC within the vacuum envelope of a gyrotron to separarate the spent e-beam from the generated rf, (2) generation of a whispering-gallery mode by injection of a Gaussian-like beam into the output end, and (3) conversion of TE _m,n modes into TE_0n modes for low-loss transmission in smooth-wall waveguide.     

Design of a low-power tunable quasioptical gyrotron with a slotted output mirror

A low-power tunable quasi-optical gyrotron was designed for driving free electron laser amplifiers in the frequency ránge of 220–270 GHz. The gyrotron cavity consisted of a spherical mirror and a plane slotted mirror to produce a Gaussian radiation output beam. Output powers of 1–10 kW were obtained in the 4 cm length cavity by a few amperes of electron beams with a voltage of 30 kV.     

Sub-nanosecond pulselength millimetre wave generation with a phase modulated quasi-optical gyrotron

It is shown that a quasi-optical gyrotron operating with a current modulated second beam can produce a train of phase-locked millimetre wave pulses.     

Operation of the quasi-optical gyrotron at harmonics of the gyrofrequency

This paper investigates the performance of a quasioptical gyrotron, when the electron beam interacts with the radiation fields at harmonics of the gyrofrequency. The nonlinear equations of motion are obtained in the slow-timescale. The expression for the linear gain is derived and the conditions for excitation are given (frequency threshold, optimal operating point, bean current and resonator quality thresholds). In the nonlinear regime, it is shown that maximum efficiencies comparable to those at the fundemental (～50%) are possible, albeit at a prohitively high radiation field amplitude, while realistically feasible field amplitudes can give somewhat smaller, but nevertheless still high efficiencies (～15%). Finally, the results are suplemented by empirical scaling laws, useful for experimental designs.     

Frequency measurement of a submillimeter wave gyrotron output

Measurement of frequency spectra of the output of a gyrotron in the millimeter to submillimeter wavelength range using a Michelson interferometer have been made. The results are compared with frequency measurements using a Fabry-Perot interferometer. A correction for mesh transmittance is used to give the true frequency spectrum. The method is used to search for the presence of higher cyclotron harmonics (n=f /f _c=3,4,…) which may be generated along with the more intense fundamentals (n=1) or second harmonics (n=2), and to study mode competition between the fundamental and the second harmonic modes.     

94 GHz回旋管准光模式变换器的数值模拟

对回旋管内置准光模式变换器进行了理论研究和数值模拟。基于几何光学理论和矢量绕射理论,编制了模拟电磁场行为的分析和优化程序,采用Vlasov辐射器和准光反射器实现了线极化准高斯模HE11。结果表明:在一级反射镜下的转换效率为88.3%,增加反射镜级数会降低转换效率。     

First experiment of gyrotron tube with quasi-optical cavity of special configuration

A new kind of quasi-optical cavity—Axisymmetrical Quasi-Optical Cavity of Oblique Rotation (AQCOR) and the new scheme for quasi-optical gyrotron with AQCOR had been proposed in [1], and the experimental tube was built in our institute. Now the initial test results of the tube are reported in this paper.     

回旋管准光辐射器研究与设计

准光辐射器是高功率回旋管准光模式变换器的重要组成部分.采用几何光学理论分析圆波导准光辐射器,根据高斯波束(TEM00模)在辐射器切口处形成的原因,利用耦合波理论设计波纹波导准光辐射器.通过编写程序并进行数值优化完成140 GHz、TE28,8模式回旋管波纹波导准光辐射器的设计,结果表明波纹波导辐射器的总长度仅为205.2 mm,切口长度为47.2 mm,在辐射器螺旋切口Brillouin区内高斯模式标量相关系数大于98%.本文所用的方法也可用于其它频率和模式的回旋管准光辐射器设计.     

A high-efficiency quasi-optical mode converter for a 140-GHz 1-MW CW gyrotron

A highly efficient quasi-optical mode converter system with several novel features has been designed and tested at Forschungszentrum Karlsruhe (FZK). The converter consists of a dimpled-wall waveguide launcher, one quasi-elliptical mirror and two toroidal mirrors. The coupled-mode theory has been used to analyze the operation of the prebunching waveguide launcher; the radiated fields from the cut of the launcher have been calculated by the scalar diffraction integral. Simulation results show that the advanced dimpled-wall launcher generates a well-focused Gaussian radiation pattern with low diffraction losses. In this case, toroidal mirrors are sufficient to obtain a desired output beam pattern. An efficiency of more than 98% has been achieved to convert the rotating TE/sub 28,8/ cavity mode at 140 GHz into a fundamental Gaussian beam. Experimental measurements show close agreement with theoretical predictions.     

回旋管准光辐射器研究与设计

准光辐射器是高功率回旋管准光模式变换器的重要组成部分.本文首先采用几何光学理论分析圆波导准光辐射器,然后根据高斯波束(TEM00模)在辐射器切口处形成的原因,采用耦合波理论设计波纹波导准光辐射器.通过编写程序并进行数值优化完成140GHz,TE28,8模式回旋管波纹波导准光辐射器的设计,结果表明波纹波导辐射器的总长度仅为205.2mm,切口长度为47.2mm,在辐射器螺旋切口Brillouin区内高斯模式标量相关系数大于98%.本文所用的方法也可用于其它频率和模式的回旋管准光辐射器设计.     

140 GHz兆瓦级回旋管高斯模式输出窗设计

根据热核聚变用140 GHz回旋振荡管研制需要,对高斯模式输出窗进行研究。以化学气相沉积金刚石作为输出窗片的材料,通过理论分析,优化设计出低反射、低吸收高斯模式输出窗片的尺寸,获得窗片半径和厚度分别为46 mm和1.8 mm。通过理论分析各参数对高斯模式透射率的影响,并利用FEKO软件进行计算验证,获得高斯模式输出窗设计参数,从而为热核聚变用回旋振荡管的研究打下技术基础。     

Experimental study of a quasi-optical cavity with slotted output mirror

This paper describes an experimental study of a quasi-optical cavity to be used in qyrotrons. The cavity configuration was designed so that its output wave could pass into a quasi-optical transmission line. The test cavity was coaxially composed of a pair of annular mirrors, one of which was a curved conical mirror and the other was a plane mirror having a radial slot array for wave output. A mode excited in the cavity at 56.4 GHz was observed by detecting the radiation wave that leaked out through the slotted mirror. It was shown that the present slotted mirror served as a partially and uniformly transparent mirror to radiate the output wave with the same mode as in the cavity.     

A depressed collector system for a quasi-optical gyrotron with precisely controlled magnetic flux lines

Design of a depressed collector system for a quasi-optical gyrotron, which had a severe constraint on the maximum allowable radius of the collector region is outlined. The needs for unwinding of spent beam and for energy sorting could be accommodated by precise control of the magnetic field profile, especially in the collector region. Techniques used for defining and obtaining such profiles; and for dovetailing the profile with the collector geometry are discussed. Results on profiles and electron trajectories are presented, which demonstrate the feasibility of the design. From primary electron trajectories a collector efficiency of up to 68% has been calculated for a three collector design.