回声增强高次谐波太赫兹倍频行波管

Terahertz radiation has important potential application in the fields of communication, observation, countermeasure and biological imaging. However, lacking of powerful, miniature source is a bottleneck to the development of terahertz technology. In this program, we present a new device, traveling wave tube multiplier based on echo-enhanced high harmonic generation effect (EEHG TWT) which was motivated by the accelerator and x-ray free electron laser. In the EEHG TWT, the electron beam is modulated by two millimeter wave, respectively. The space phase of the beam will fold and rotate in its evolution progress and a series of sub-bunches was formed. So the specific high harmonic current was enhanced and others are depressed. Then the terahertz wave was excited by the sub-buncheds and amplified. The EEHG TWT is an amplifier and does not rely on the operating (beam) voltage to tune the output frequency. Rather, the output frequency is tuned continuously over a wide bandwidth through the input signal frequency and is insensitive to beam-voltage jitter. This new device also takes advantage of lower-cost and more mature millimeter wave sources, instead of a state-of-the-art solid state THz amplifier, as its driving source. The program will discover the echo enhanced harmonic generation process in the nonrelativistic electron beam and its application in the traveling wave tube. We will investigate the high harmonic generating, enhancing and choosing by 3-dimensional large signal analysis and particle-in-cell simulation. Also the influence of the cathode temperature，space charge effect and focusing magnetic field will be discussed. Then the method to improve the efficiency of the device will be provided. Finally，The EEHG TWT will be designed and fabricated to verify the theory by the experiment. The products of the research will make a fundament for the development of practical high power mini size terahertz wave source.

太赫兹技术发展的主要瓶颈之一是缺乏大功率、小型化的信号源。课题将加速器和自由电子激光中的回声增强效应应用于行波管，提出一种新型大功率小型化太赫兹源：回声增强高次谐波倍频行波管。 这种器件的特点是电子束流分别经两次输入信号调制，在相空间产生折叠、旋转，形成一系列子群聚束团，使得特定高次谐波电流得到增强，同时其他谐波被抑制。 器件由成熟的毫米波信号源驱动，经谐波电流激励起太赫兹波并放大，输出调谐范围宽，且不受束电压波动影响，频率稳定性好，功率容量大，制作工艺与普通行波管兼容。 课题以非相对论电子束流的回声增强高次谐波产生机理及其在太赫兹波倍频行波管中的应用为研究目标，通过三维大信号分析与粒子模拟，揭示高次谐波产生、增强与选择机理和热初速、空间电荷效应和聚焦磁场等因素对谐波电流的影响；提出提高器件电子效率的方法、设计器件并进行制管实验验证，为研制新型太赫兹波段小型化大功率源奠定基础。

太赫兹技术发展的主要瓶颈之一是缺乏大功率、小型化的信号源。项目提出一种新型的大功率小型化太赫兹源，回声增强高次谐波太倍频赫兹源，这种器件可由成熟的毫米波信号源驱动，得到太赫兹波段的大功率信号输出，并具有结构紧凑、工作稳定的优点，有望解决上述小型化大功率太赫兹源缺乏的问题。.项目建立了回声增强高次谐波折叠波导行波管三维大信号分析模型，模型考虑了热初速、散粒噪声、空间电荷效应等影响，可以得到更精准的计算结果，据此模型编制了计算机分析软件，可以有效的到器件的输出功率、增益、效率等各项参量。建立了高次谐波行波管粒子模拟模型，通过计算，揭示了电子束折叠、旋转的机理，提出了操控非相对论电子束流的有效方法，研究了输入信号调制、束流群聚、谐波激励和放大的物理过程并得到其物理图像，并研究了热初速、散粒噪声、空间电荷效应对电子束传输和电磁波激励的影响。.完成了高次谐波短毫米波与太赫兹波行波管的分析与设计，提出了电子束调制、漂移群聚、谐波激励各部分的设计理论，给出了高次谐波倍频行波管的设计方案，提出一种新型的级联高次谐波器件并完成了设计，克服了谐波倍频器件效率低的问题。.研制出百瓦级低波段（Q波段）折叠波导行波管与瓦级高波段（D波段）折叠波导行波管，详细研究了折叠波导慢波结构深度调制与带宽拓展的优化设计以及漂移段长度对群聚参量的影响，完成了电子束完成了器件的电子枪与周期永磁聚焦系统、匹配衰减器、过渡波导和输能窗等关键部件的研发，在此基础上，设计、加工、组装成功短毫米波3次谐波倍频，器件由Q波段信号输入，得到D波段输出，功率300-500毫瓦，高次谐波的放大机理成功得到了实验验证，所研究成果在伦敦国际真空电子学会议上作了口头报告，得到与会专家好评，并作为优秀论文，推荐到IEEE Transaction on Electron Device上发表。为小型化的太赫兹源研究开辟了新的道路。