基于大回旋电子注的超高谐波太赫兹回旋管研究

Gyrotron operates on the principle of the relativistic electron cyclotron maser. Because the operating frequency is controlled by the applied magnetic field, the gyrotron can overcome the limitation of the device-dimension-and-operating-wavelength correlation that usually limits the performance of conventional vacuum electronic devices. Accordingly, the gyrotron is capable of radiating high-power electromagnetic-wave radiation in the range of millimeter-to-terahertz band. However, under the fundamental harmonic operation, present technique of superconducting magnet can only support developing gyrotron with frequency less than several hundred GHz. In order to further extend the gyrotron operating frequency, this project proposes systematically investigating the ultra-high harmonic gyrotron which excites radiation on the fourth harmonic frequency of the electron cycling motion. Accordingly, high-performance continuous-wave-operation gyrotron with frequency up to ~1THz can be developed with the present available superconducting magnet technique. An axis-encircling large-orbit electron beam (LOB) with the unique capability of the directional mode coupling and low-temperature cooling of the interaction cavity will be applied to solve the serious challenges of harmonic mode competition and low-efficiency harmonic interaction, respectively. We are going to carry out systematic investigations, including ultra-high harmonic beam-wave interaction, low-velocity-spread LOB electron generation, ultra-high harmonic gyrotron tube integration, and accurate high-power THz wave manipulation and diagnosis. Finally, we will present a detailed scheme of high-performance continuous-wave ultra-high harmonic gyrotron covering the 1-THz band and develop the world’s first prototype installation of ~1THz 4th harmonic LOB gyrotron. This work is going to promote innovative applications of THz science and technologies in the fields of national security, bio-medical science, and material science, and so on.

回旋管采用相对论电子回旋谐振受激辐射原理工作，其工作频率由外磁场决定，突破了传统真空电子器件尺寸与波长的共度性限制，具备在毫米-太赫兹波段产生大功率辐射的能力。然而，在基波工作条件下，当前超导磁体技术仅能支持发展几百GHz的回旋管。为了进一步提高回旋管的工作频率，拟开展超高谐波回旋管研究，在电子的4倍谐波回旋频率上激发辐射，进而发展出基于现有超导磁体技术的~1THz高性能连续波回旋管。拟采用具有独特锁模能力的共轴大回旋电子注（LOB）和低温冷却互作用腔以分别解决超高谐波回旋管面临的严重模式竞争和低效率问题。通过开展高性能LOB、超高谐波注-波互作用、太赫兹回旋管整管集成和大功率太赫兹波测控等系统性的研究工作，探索出可覆盖1THz的超高谐波连续波回旋管方案，研制出国际上第一支~1THz的4次谐波超导回旋管样管，推动太赫兹科学技术在国家安全、生物医学和材料科学等领域的创新应用。

大功率太赫兹波源是推动太赫兹科技发展的关键。共轴大回旋电子注推动谐波回旋管能够在电子回旋频率的谐波上辐射电磁波，推动器件实现更高的极限工作频率。本课题首先开展了关于谐波互作用腔、大回旋电子枪和准光系统的理论研究，为解决键科学问题、系统设计和器件研制提供重要的理论依据。其次，本课题通过深入研究渐变会切磁场产生大回旋轨道电子注的物理机制，提出了“共型交叉流”技术，有效解决超高磁压缩比下大回旋电子束电流低、品质差的问题。结合电子注-波互作用理论，开展了对低温冷却腔体和大回旋高次谐波互作用的研究。集成上述研究基础，开展回旋管各级子系统的研制、性能测试和测试平台集成。本课题开展了包括大回旋电子枪、谐波回旋管系统、高场超导、高压电源调制器和太赫兹波诊断系统等系统性的测试平台建设工作。发展出1THz超高谐波回旋管方案、研制出原型样管，开展了太赫兹回旋管的系统测试，工作磁场介于3.8-9.1T（电子回旋频率是基波100-240GHz、二次谐波200-480GHz、三次谐波300-720GHz），并且侦测到了一系列基波和谐波模式的太赫兹波辐射信号，最高基波功率约1.57kW、二次谐波功率约0.8kW，三次谐波功率0.32kW，验证了大回旋电子注谐波回旋管方案在太赫兹频段工作的可行性。这也是国内太赫兹频段的首套大回旋电子注回旋管实验，相关成果为后续国内研发高性能大回旋谐波回旋管的奠定了重要理论与技术基础。研究工作还拓展研究自由电子与人工材料互作用系统中的电磁波辐射问题，在系统集成化和激发高阶道角动量波束方面有重要潜力。.发表学术成果70篇/项，其中包括Laser & Photonics Reviews、ACS Photonics、Journal of Light Wave Technology、IEEE Transactions等期刊论文共计39篇，会议论文31篇，国家发明专利12项。基于本课题共培养相关领域专业人才共20名，其中博士研究生10硕士研究生10名。在专业人才的培养过程中，获得重要奖励、荣誉等共13项。成果支撑团队骨干获得国际奖项“真空电子学青年科学家”（年度唯一、首位华人获奖者）1项、北京市基金委杰青1项。