同轴相对论返波管波束作用物理机制研究

Coaxial relativistic backward wave oscillator (CRBWO) is a new type of high power microwave (HPM) source device remarked by the high efficiency. While CRBWO works with the high efficiency, the physical mechanism of its wave-beam interaction is notably distinguishing from that in the hollow RBWO. The electron beam interacts synchronously with the forward harmonic, and the frequency range of the synchronous interaction is considerably wide, which is likely to induce the mode competition. The energy exchange significantly occurs between the electron beam and the asynchronous harmonics. The mode competition can be depressed when the amplitudes of -1st harmonic，i.e., the asynchronous harmonic, and the synchronous harmonic are close to each other. At present, little research has been done on the physical mechanism of the wave-beam interaction in CRBWO, especially on the asynchronous wave-beam interaction and the effect of the -1st harmonic on the mode competition. Our study aims to study the physical mechanism of the wave-beam interaction by establishing theoretical model based on the inherent characteristics of CRBWO. The impact of the important operation parameters on the structure wave is analyzed. And the performance of the synchronous and asynchronous harmonics in the beam modulation and the energy exchange is investigated. Consequently, the physical mechanism of the wave-beam interaction in CRBWO can be presented and described exactly according to the amplitude ratio and the phase relation between the synchronous and asynchronous harmonics. Based on the theoretical results we will put forward the design method to depress the mode competition and to achieve the high output efficiency under the diode voltage of 1 MV. Our research lays the theoretical foundation and provides the technical support for the further development and the practical application of CRBWO.

同轴相对论返波管（CRBWO）是一种新型高效高功率微波（HPM）产生器件。实现高效输出时，CRBWO的波束作用具有不同于空心返波管的特点：电子束流与前向波发生同步作用，作用的频率范围很宽，可能诱发模式竞争；电子束流与非同步波发生显著能量交换，当-1次空间谐波(非同步波)与同步波幅度相近时，模式竞争得到抑制。目前，对CRBWO波束作用物理机制并无清晰认识，特别对非同步波束作用和-1次空间谐波对模式竞争的抑制缺乏充分研究。本项目针对CRBWO波束作用的特点建立理论模型，分析重要工作参数对CRBWO结构波特性的影响，研究同步波与非同步波在束流调制和能量交换中的作用，根据同步波与非同步波的幅度之比和相位关系，揭示CRBWO波束作用的物理机制。基于理论研究，探索并提出二极管电压1 MV水平下抑制模式竞争、实现高效输出的CRBWO设计原则与方法，为CRBWO的进一步发展和实用化提供理论基础和技术支持。

本课题通过解析理论和数值模拟对CRBWO这样一种新型HPM产生器件进行了系统深入的研究。利用小信号理论和线性理论对有限长同轴SWS的高频特性进行了深入研究，将原有的用于无限长结构的方法推广到有限长结构，建立了分析有限长同轴SWS高频特性的普适性方法。从空间增长率的角度分析了有限长同轴SWS的纵向谐振特性和起振条件。深入研究了同步波与非同步波在波束作用中的作用机制和物理过程，在考虑基波和-1次空间谐波与电子束流的共同作用、考虑非同步谐波与电子束流能量交换的基础上，建立CRBWO波束作用理论模型，综合得到CRBWO中波束作用的物理机制与过程。重点研究同轴SWS两端反射对CRBWO结构波中同步波与非同步波物理特性的影响规律，及其对束流调制和能量交换的影响规律。理论研究表明，当同轴SWS末端形成全反射时，波束作用转换效率接近60%。在理论研究的指导下，设计了转换效率达到55%的衍射式CRBWO。在大幅度提高输出指标的同时，从根本上改进了同轴装配装方式，解决了这种器件由于结构复杂而无法有效保证同轴度的问题，增加了这种新型器件的实用性。从理论上分析得到了高电压下波束失配的物理原因。并提出了单管同轴双阴极的结构，有效解决了高电压下电子束流结构波失配的问题，并实现了输出功率5 GW、效率45%的X-band输出。并且，为适应HPM产生器件低磁场、小型化的发展趋势，提出了有别于传统Cerenkov机理、无SWS的同轴TE01模式周期交变磁场产生器件，在X-band和Ka-band实现了102 MW、转换效率大于20%的微波输出，在实现永磁包装的同时显著提高了器件的功率容量。