Study On The Radiation Sources Of Millimeter And THz Waves Driven By The Periodic Electron Bunches

Millimeter and THz waves with the unique advantages in the electro-magnetic spectrum are very important for the national defense military and civil applications. The radiation sources are one of the keys to develop the applications of millimeter and THz waves. The vacuum electronic devices based on grating, such as the backward wave oscillator (BWO), Orotron and Smith-Purcell (SP) radiation source, are promising candidates in developing the compact, powerful radiation sources at the band of millimeter and THz waves. As the development of the photocathode injector and the rf accelerator, a renewed interest in the coherent radiation using a train of tiny electron bunches produced by a rf accelerator has been raised in the recent years.The coherent millimeter and THz radiation generated by the periodic bunches is studied in this dissertation. The major achievements are as follows:(1) The properties of SP radiation generated by the electron bunches, are analyzed in detail.The theoretical analyses show that the angular distribution and radiation frequency strongly depend on the electron energy, the size of the bunch, the electron bunch shape, and the type of grating. According to the numerical calculations, the radiation can operate at millimeter wave or THz with feasible parameters for the bunches and the grating.(2) Particle-in-cell (PIC) simulation is used to investigate the properties of the THz wave band SP (THz-SP) radiation generated by the periodic electron bunches and continuous beam, respectively. The results show that the radiation from the bunches is more efficient than that from a continuous beam.Then we are very interested in developing the coherent radiation sources based on the periodic bunches.(3) A new approach to generate coherent SP radiation from a two-section model is proposed. Based on the mechanism of Cherenkov device, a continuous beam is effectively prebunched in the first section, and then the coherent THz SP radiation is stimulated by the bunched beam in the second section. Instead of the rf accelerator, the periodic bunches are generated by itself in this scheme, and the cost of the source will be reduced.(4) An 8 mm wave band RDG with two-section slow-wave structure and coaxial rippled-wall-tapered reflector is studied in detail. The experiment results show the output power is enhanced by use of the sectional system.Optimizing the magnetic field of RDG, the TE₁₁ mode, which is appropriate for power radiation, can be generated, and the output power also arrives at maximum.Experimental results are in accordance with those of the simulation results.