【作者】 张辉波；

【导师】 张世昌；

【作者基本信息】 西南交通大学 ， 通信与信息系统， 2013， 博士

【摘要】 太赫兹波泛指频率介于远红外和微波频段之间的电磁辐射,由于其在电磁波谱中所处的特殊位置,因而具备许多独特性质,在雷达、通信、材料处理、成像等领域有着广泛的应用前景。随着太赫兹波应用的日益广泛,研制有效的太赫兹辐射源成为世界各国在该领域的研究热点之一。基于电子回旋受激辐射原理发展起来的快波回旋器件——回旋管,被认为是目前最能获得高功率(上百千瓦及以上)输出的太赫兹辐射源。工作在太赫兹频段的传统圆柱腔回旋管工作在低阶模式,横向尺寸较小,这给加工及散热带来一定困难,导致输出功率受到限制。而采用同轴结构的回旋管谐振腔,由于其特殊结构可以抑制高阶模式竞争,进而可以增大其腔体横向尺寸,从而可以获得更大的功率输出。目前,关于同轴腔回旋管的实验研究,主要是为国际热核聚变(ITER)提供高功率电磁辐射源,其频率最高为170GHz,功率可达2.2MW。而对此结构下更高频率辐射的回旋管的研究,尚未见诸报道。同轴腔回旋管要获得高功率太赫兹波输出,有两个须得解决的主要问题：一是要尽可能地增大腔体的横向尺寸以利于加工和散热,二是尽可能降低工作磁场以利于降低工程成本。本文旨在探索并用非线性方法研究基于同轴结构回旋管原理,采用高阶模式高次谐波,在较低工作磁场条件下实现单模高功率太赫兹波输出的可能性。本文的编排如下：第一章详细介绍了太赫兹辐射源(尤其是基于电子回旋脉塞机理)的研究现状以及存在的主要问题,进而给出本文的研究内容以及意义所在。第二章建立了同轴腔回旋管振荡器多模起振模型。首先建立了同轴腔体中各个模式的冷腔体分析模型,并利用FORTRAN语言编制了相应程序,可在给定腔体结构下计算出相应模式的谐振频率,绕射因子以及冷腔体场分布；然后给出了多个模式在冷腔场分布下的起振模型,推导了起振过程中开槽深度较浅情况下各模式在外壁和内导体上的欧姆损耗的近似表达式,并提出了相应的数值计算方法,进而编写了考虑模式竞争和欧姆损耗的多模起振程序。第三章利用卡尔斯鲁厄研究中心(KIT)开展的TE34.19模式基次谐波、工作频率0.17THz同轴回旋管实验数据进行数值计算,模拟了多模起振过程,所得结果与实验报导较为吻合,验证了本文多模起振模型及所编程序的可靠性。第四章详细设计研究了一种工作在高阶模式TE42,22、工作频率为0.22THz的一种新型的同轴腔回旋管振荡器。首先确定了其腔体参数和竞争模式,进而研究内导体开槽以及取负坡度对于抑制模式竞争的影响。数值分析表明,内导体合适的开槽以及适当的坡度选择不仅可以稀化模谱,还可以降低竞争模式的绕射因子,从而提高其起振电流。在优化后的电子束导引中心半径下,通过对考虑不同旋转方向模式的多模起振过程的模拟,表明所设计器件可以在65kV-75kV的电压范围内,稳定地工作在单一模式下,最大输出功率可达0.8MW,其腔体损耗小于腔体壁所能承受的最大值。第五章研究设计了一种超高阶模式高次谐波(TE43,4三次谐波)工作频率为0.34THz、功率输出上百千瓦的同轴腔回旋管振荡器。在三次谐波起振过程的研究中发现,由于模谱太密和与电子束互作用相对较弱,普通高阶模式的三次谐波难以从激烈的模式竞争中起振。而采用边廊模式(即角向模式指数远大于径向模式指数)可以有效地克服模式竞争。通过对内导体开槽深度对基波模式参数影响的分析,选取合适的开槽深度将大大稀化其与工作模式之间的频率分割度,进而有效地抑制来自基波的模式竞争。多模起振的数值分析表明,三次谐波模式可以稳定地工作在相对较小的一个加速电压范围,并获得163kW的功率输出。更多还原

【Abstract】 Terahertz (THz) wave, which means the electromagnetic radiation between far infrared and microwave region, occupies a special position in the electromagnetic spectrum and consequently has a lot of unique characteristics. It has widely potential applications including radar, communications, material processing, imaging and so on. With its applications more and more widely, it becomes a research hotspot in this field for many countries in the world to develop an effective THz radiation source. Gyrotron—one of the fastwave gyro-devices, based on the mechanism of ECRM, has been considered to be the most promising THz radiation source to generate high power (over100kilowatt).Because of the low-order operating mode, the transverse size of the traditional cylindrical cavity THz gyrotron is small, which causes problems in machining, ohmic heating and further increasing of output power. Meanwhile, as far as the coaxial cavity is concerned, the high-order mode could be employed due to the suppression of competition modes even with much denser mode spectrum, which could increase the cavity diameter and output power.Currently, the main aim of the coaxial cavity gyrotron experiments is to provide the microwave radiation source for ITER, the highest operating frequency is0.17THz and the corresponding power is2.2MW. So far the research on the coaxial cavity gyrotron with higher operating frequency has never been reported.To generate the high power THz radiation by employing coaxial cavity gyrotron, two main problems have to be solved:1) Increasing the transverse size of the cavity as large as possible on benefit of machining and heating;2) Decreasing the working magnetic field as low as possible to reduce the engineering cost. This paper aims to use the nonlinear method to verify the possibility of single-mode high power THz radiation based on the coaxial cavity gyrotron with high-order modes, high harmonics and low magnetic field.This dissertation is organized as follows:In Chapter1, the detailed states of the arts of THz coaxial cavity gyrotron and existing problems are introduced, the contents and value of the work are also presented.In Chapter2, the multimode startup model in the coaxial cavity gyrotron oscillator is established. Firstly, the model of the cold-coaxial-cavity analysis is established, and the corresponding program is completed by employing FORTRAN language, by which the resonant frequency, diffractive factor and cold-cavity field distribution of each mode could be obtained with provided cavity parameters. Secondly, the multimode startup model with assumed cold distribution is given, the ohmic losses on inner rod and outer wall of each mode provided shallow slot depth are derived, the numerical mothed is presented and the time-dependent, multimode code with the ohmic losses taken into account is developed.In Chapter3, by use of the parameters of the fundermental TE34,19,0.17THz coaxial cavity experiments in KIT, the numerical calculations are performed to simulate the multimode startup scenario. The results agree well with the experimental report, which demonstrates the validity of the multimode startup model and program.In Chapter4, a coaxial cavity gyrotron with0.22THz operating frequency is designed in detail. The cavity parameters are selected and the corresponding competiting modes are confirmed. The influence of proper corrugated inner condunctor with slope on the mode competition is analyzed. The results indicate that it can rarefy the mode spectrum and decrease the diffractive factor of the competiting modes, which leads to the rise of the starting current. Under the optimal electron guiding-center radius, the multimode startup simulations with the different rotating modes taken into account show that the maximum output power of0.8MW could be attained for the expected mode within the region of65kV-75kV, and the maximum heating losses are under the limitation.In Chapter5, an ultra high-order mode, high harmonic(TE43,4,3rd harmonic) coaxial-cavity gyrotron oscillator with over100kW output power is designed. It is found that the conventional3rd high-orde mode could hardly startup because of the fierce mode competition and weak interaction with electron beam. The problem could be solved to some degree by employing the whispering gallery mode. Through the analysis of the influence of the slot depth on the resonance frequency, it is found that the mode spectrum between the operating mode and the most important competiting fundermental mode could be rarefied greatly by the proper selection of the slot depth. Nonlinear simlulation shows that the maxim output power of163kW for the operating mode is obtained, and the single-mode operation is achieved in a comparatively narrow region of accelerating voltage.更多还原