脉冲功率电子束获得GW级调谐太赫兹辐射的技术研究

Research involving Terahertz spectrum spanning from 100 GHz to 10 THz has been experiencing a rapid growth in the past decades. The growth is application driven with interests from chemical and astronomic spectroscopy and sensing, medical and biological imaging and analysis, security and safety screening, material research and semiconductor industry, next generation communication networks and radars, etc. Recently, many THz applications have become closer to reality with the rapid advancing of THz sources, detectors, and other novel components. .THz source is a crucial part of THz science and technology. Breakthroughs in THz sources will greatly promote the THz applications. Due to their specific location on the electromagnetic spectrum, approaches for developing THz source can be classified into two general categories: optical technology and electronic technology. Optical THz generation can cover almost the whole THz frequency band, such as optical pumped THz laser, photoconductor, optical rectification (OR), difference frequency generation (DFG), optical parametric oscillation, and four wave mixing in air-plasma. THz generation via optical approaches, especially nonlinear optical frequency conversion, is an established way. .The free-electron laser (FEL) can produce high power coherent radiation in the terahertz region. Also, the wavelength can be continuously tuned, the pulse length can be very short, and the intensities can be very high. These attributes make the FEL extremely attractive as a coherent THz radiation source. The appealing features of FELs (e.g. their tunability and high output power) are usually counterbalanced by some drawbacks, such as large size, high cost and system complexity. Nevertheless, most sources cannot generate THz beams with great power in the THz region, while the FEL can also meet the requirement for compactness in the THz region. Also, the technical requirements of the electron accelerator used in an FEL relax as the wavelength increases, and thus there are a number of opportunities for cost-effective scientific applications of FELs in the far-infrared region. Many applications have been proposed in this spectral region, ranging from solid-state physics to biophysics and nuclear physics..We report the generation of intense tunable THz from THz FEL in a strong guiding magnet field. Field emission cathode (driven by the LTD pulse generator) is installed inside a superconducting magnet, and electron’s radial movement is guided by the guiding magnet field. Being small sizes of ~1.5 m long, electron beam with radius of ~1.0mm and current of kAs is obtained to make SASE THz FEL occurred in a electric wiggler. The electric wiggler, which is made of electric electrode, can be installed inside a superconducting magnet. Driven by the LTD pulse generator, the electron is accelerated by the electric field between the cathode and the anode. So, GW THz (0.37-1.04THz) radiation can be generated with the aid of the strong guiding magnet field.

结合FEL成熟理论、脉冲功率和超导磁铁两项成熟的前沿技术，采用脉冲功率驱动的磁沉浸阴极来提供满足FEL要求的电子束和静电摇摆器，形成一个能产生GW级太赫兹辐射、同时体积小、运行成本低和维护容易等特点的新技术路线，研究内容有：1）电子束品质，电子束流强数kA，引导磁场使电子从阴极表面发射后沿磁力线运动，从而满足FEL互作用的要求；2）静电摇摆器，摇摆场由电极来提供，将电极完全埋在绝缘介质，使摇摆器不仅同强引导磁场兼容，而且摇摆静电场也能满足FEL的要求。已经开展了可行性研究有：1）VSim 软件模拟，有明显的THz辐射（模拟效率~10%）；2）结合现有的超导磁体（B=5T、孔径200mm）加工了静电摇摆器，在强磁场下耐压达到了200kV，对应的K~0.4。

在本项目中，本项目组结合FEL成熟理论、脉冲功率和超导磁铁两项成熟的前沿技术，采用脉冲功率驱动的磁沉浸阴极来提供满足FEL要求的电子束和静电摇摆器，并形成了一个能产生GW级太赫兹辐射、同时体积小、运行成本低和维护容易等特点的新技术路线，在本项目中本项目组创建了满足引导磁场使用要求的静电摇摆器，并使用该装置进行了相关实验，并结合CST程序对实验进行了模拟并取得了良好的结果。本项目主要取得以下主要成果：1）进行了满足引导磁场使用要求的静电摇摆器的设计；2）研究了在引导磁场和静电摇摆场共同作用下电子的摇摆运动；3) 对引导磁场下的一维SASE FEL物理过程进行了分析，并据此给出了SASE FEL的工作条件；4）根据SASE FEL对电子束参数的要求，使用PIC模拟程序对金属场发射电子在引导磁场下的运动进行了深入的研究，对阴、阳极结构进行了优化设计，使电子束的参数满足要求；5）开展了不同电压下的束波互作用的模拟。项目发表第一标注SCI论文8篇，完成学术专著1部。培养博士生2人，硕士生5人（已毕业2人），已经超额达到了项目预期的目标。