【作者】 刘文鑫；

【导师】 梁正； 杨梓强；

【作者基本信息】 电子科技大学 ， 光学， 2008， 博士

【摘要】 由于毫米波及亚毫米波在电磁波谱中的独特优势,使其在军事和民用两方面都存在广泛的应用前景,而源是毫米波及亚毫米波能否被利用的核心。在毫米波及亚毫米波波段,自由电子激光(Free-electron lasers,简称FEL)是一种重要的大功率、频率可调的辐射源;另一方面,基于光栅结构的真空电子器件如BWO、Orotron、SP辐射源等器件,既可以发展成为紧凑、小功率的辐射源,也可以发展成为高功率的辐射源,因而受到广泛的关注。基于这种原因,本论文探讨了利用双流不稳定性的机制改善这些器件的性能,对双电子注器件中注波互作用的特性进行了理论分析、粒子模拟和实验三个方面的深入研究,结果表明引入双电子注可明显改善这些器件的性能。本文的主要工作如下:(1)提出了具有引导磁场的双电子注自由电子激光(FEL)。通过线性流体理论推导了具有引导磁场双电子注FEL的色散方程,并且进行了求解。结果表明:引入轴向磁场,不仅可以提高双电子注注波互作用的线性增长率,而且可以增加带宽;双电注处于最佳的速度差和电流比时,注波互作用的增长率得到了较大的提高。(2)研究了双电子注平板封闭光栅Cherenkov器件。利用流体理论和场匹配的方法,导出了双电子注情况下的色散方程。理论分析表明:由于存在双流不稳定性,使得双电子注器件的线性增长率较单电子注有明显的增加;粒子模拟表明,双电子注处于最佳电压比和电流比时,双电子注器件的辐射功率得到了显著的提高。(3)创新性地引入了双流不稳定性机制改善平板开放光栅SP器件的辐射性能。通过色散方程的求解和分析,表明在注波互作用的同步点,由于双流不稳定性,双电子注系统的线性增长率得到了明显的提高。粒子模拟表明:采用双电子注不仅可以提高SP辐射的功率、缩短饱和时间,而且可以降低起振的阈值电流。(4)研究了双电子注圆柱光栅毫米波辐射源。利用流体理论和场匹配的方法导出了分立双电子注激励圆柱光栅的色散方程,并进行了求解。结果表明:双流不稳定性改进了线性增长率。粒子模拟研究表明:双电子注系统较之单电子注系统可以获得更大的辐射功率;同时研究了双电子注之间距离对器件性能的影响,模拟发现双电子注之间的距离增大,双流不稳定性减弱,导致辐射功率快速衰减。(5)在国内首次进行了相对论双电子注绕射辐射振荡器(RDG)的实验。氖管阵列屏测试出毫米波辐射主要是对称的TM模式,利用色散延迟线测试到频率为30.27GHz;测试到双电子注RDG的辐射功率为189.69MW,而单电子注RDG的辐射功率为139.44MW。实验结果表明:采用双电子注有利于提高器件的辐射功率和增加信号脉冲宽度。更多还原

【Abstract】 Millimeter and submillimeter waves with the unique advantages in the electromagnetic spectrum are very important for the national defense military and civil applications. However, the radiation sources are one of the keys to develop the applications of millimeter and submillimeter waves. At the band of millimeter and sub-millimeter, Free-electron laser (FEL) is one of important radiation sources of high power and tunable frequency. On the other hand, the vacuum electron devices based on grating, such as the backward wave oscillator (BWO), Orotron and Smith-Purcell (SP) radiation source, are widely attentive by the researchers, for which are a promising alternate of the development of tunable, compact, powerful radiation source. In this dissertation, an approach of using two-stream intability (TSI) to improve the performances of such kinds of devices is presented. The detailed investigations on the beam-wave interactions of the two electron beams device have been performed through the theoretical analyses, particle-in-cell (PIC) simulations and experiment study. The research results show the performances of devices are markedly enhancement due to the two beam interactions. The major achievements of this dissertation are as follows:(1) The two-stream free-electron laser (FEL) with an axial guiding magnetic field (AGMF) is presented. The dispersion equation with an AGMF is derived with the help of linearized fluid theory and solved numerically. The results show that the linear growth rate of beam-wave interaction is enhanced and band width is enlarged as the presence of AGMF. Moreover, a considerable enhancement of growth rate maximum is obtained at the the optimum velocity separation and current ratio of two electron beams.(2) The two electron beams planar closed grating of Cherenkov device is studied. The dispersion equations are derived and solved, the results show the linear growth rate and band width of two electron beams device are larger than that of single beam due to the TSI. The results of PIC simulation show that the radiation power of two electron beams Cherenkov device is obtained a considerable enhancements at a suitable voltage ratio and current ratio. (3) A novel approach to the enhancement of SP radiation employed the TSI in planar open grating is presented. The planar open grating is driven by two electron beams that propagate over the grating with a velocity separation. Through the solutions and analyses of dispersion equation, the results show that the linear growth rate of the two electron beams system can be achieved a considerable improvement at the synchronization point due to the TSI. With the help of PIC simulation, the enhancement of SP radiation power, the shortened saturated time and the lessened threshold current are observed(4) The millimeter radiation source of cylindrical grating driven by two electron beams is studied. The dispersion equation of two separated beams in the cylindrical grating is derived and solved. The results show that the linear growth rate is markedly enhanced due to the TSI. The PIC simulation results show that the radiation power of two beam system is larger than that of single beam. On the other hand, the effect of distance between the two electron beams on the on the performamance is investigated. The PIC results show the TSI is weakened with the increasing of two electron beams separated distance, resulting in the sharp decrease of radiation power.(5) For the first time, the experiment of millimeter-wave-band relativistic diffraction generator (RDG) driven by two electron beams is projected and performed. Main radiation mode of the device tested by neon tube array is TM symmetry, and with the help of dispersion delay line, the measured radiation frequency is 30.27GHz. The radiation power of two beams RDG and single beam RDG are 186.69MW and 139.44MW, respectively. The experiment results show the radiaton power is enhanced and the pulse width is increased by use of two electon beams.更多还原