DFG-RSF: Generation of Ultrashort Pulses in Millimeter and Submillimeter Bands for Spectroscopy and Diagnostic of Various Media Based on Passive Mode-locking in Electronic Devices with Nonlinear Cyclotron Absorber in the Feedback Loop.

该项目计划在DFG-RSF联合研究合作框架内运行，即IHM、KIT、卡尔斯鲁厄和IAP-RAS、下诺夫哥罗德之间。本建议书描述了整个项目，包括RAS和DFG部分。DNP-NMR功能的显著改进（灵敏度、分辨率、数据采集速度等），以及监视各种介质的其它方法（例如，密集聚变等离子体诊断）可以使用具有可控光谱的亚毫米范围辐射源来实现。所需的频谱控制不仅提供了在宽范围内的中心频率的平滑扫描，而且还产生了具有相关相位和可调重复率的短脉冲的周期序列。本项目旨在开发在真空电子放大器（包括陀螺谐振放大器）的基础上产生和放大毫米和亚毫米频率范围的强大宽带相干信号的方法。首次提出了在真空电子器件的基础上研究类似于被动锁模方法（广泛应用于激光物理学）的脉冲产生机制。为此，在发生器的反馈回路中放置了一个非线性幅度滤波器，该滤波器吸收小幅度的微波信号并传输高功率的信号。该滤波器预计将在非线性回旋吸收机制的基础上实现。该项目的理论方案包括在分析和计算机模型的框架内对产生超短脉冲的新机制进行详细分析，以及将结果与被动锁模机制中激光系统的已知特性进行比较。在理论分析的基础上，研制了超短脉冲发生器的实验样机，实验部分包括基于回旋吸收效应的非线性幅度滤波器的实现和性能研究，演示了当现有的长毫米波长回旋行波管时产生超短脉冲的机制（工作频率30 GHz）用作放大元件。同时，螺旋波纹回旋行波管的频率为260 GHz的关键要素，以及适合于这个频率范围的非线性回旋吸收器将被开发。

The project is planned to run in frame of a joint DFG-RSF research collaboration, namely between IHM, KIT, Karlsruhe and IAP-RAS, Nizhny Novgorod. This proposal describes the full project including both, RAS and DFG parts. Significant improvement of functionality of DNP-NMR (sensitivity, resolution, data acquisition speed, etc.), as well as other methods of monitoring the various media (e.g., dense fusion plasma diagnostic) can be achieved using submillimeter range radiation sources with controllable spectrum. The required spectrum controlling not only provides a smooth sweep of the center frequency over a wide range, but also the generation of a periodic sequence of short pulses with a correlated phase and adjustable repetition rate. This project aims for the development of methods for the generation and amplification of powerful wideband coherent signals of millimeter and submillimeter frequency range on the basis of vacuum electron amplifiers (including gyro-resonance amplifiers). For the first time it is proposed to investigate a mechanism of pulse generation similar to the method of passive mode locking (widely used in laser physics) on the basis of vacuum electronics devices. For this purpose, a nonlinear amplitude filter - the element that absorbs microwave signals with small amplitude and transmits signals with a high power - is placed into the feedback loop of the generator. The filter is expected to be implemented on the basis of the non-linear cyclotron absorption mechanism.The theoretical program of the project includes a detailed analysis of a new mechanism to generate ultrashort pulses within the framework of analytical and computer models, as well as a comparison of the results with the known characteristics of laser systems operating in the passive mode locking regime. Based on the theoretical analysis, the development of an experimental prototype of the ultrashort pulse generator will be performed.The experimental part of the project includes the implementation and study of the properties of non-linear amplitude filter based on the effect of the cyclotron absorption, demonstrating the regime of generation of ultrashort pulses when an existing long-mm wavelength gyro-TWT (operating frequency of 30 GHz) is used as the amplifying element. In parallel, the key elements for a helically corrugated gyro-TWT with a frequency of 260 GHz, as well as a non-linear cyclotron absorber appropriate for this frequency range will be developed.