Smith-purcell, Radiation Of Periodic Electron Bunches

The characteristic of Smith-Purcell radiation (SPR) from the periodic electron bunches moving above the grating is studied in this dissertation.First,based on the integral method and the modal matching method, the angular distribution of SPR energy from the triangle grating, sinusoidal grating and rectangular grating is investigated. According to the analysis based on the chosen parameters, the grating's profile and parameters affect the angular distribution of SPR energy greatly. It is also affected badly by the longitudinal distribution of bunch. Not only the angular distribution of radiation energy can be changed, but also the frequency corresponding to the max of it moves rapidly. The range of the angular distribution of radiation energy changes at the same time. Compared with the longitudinal distribution, the latitudinal distribution and the energy of bunch influence the angular distribution of radiation energy less. When the frequency is less than or equal to 0.1THz, the superradiant emission occurs and the angular distribution of radiation energy grows in proportion to the square of the electrons'number in one bunch. If the parameters are changed, the superradiant emission can also happen in higher frequency. According to the numerical calculation, the angular distribution of radiation energy grows in proportion to the square of the bunch's number for the periodic bunches. The angular distribution of radiation energy from the sinusoidal grating changes more simply and regularly along with the variety of the frequency and its value is also greater than the others.The complex grating is obtained by adding a tiny slot in the metal surface of the rectangular grating. The angular distribution of SPR energy from it is studied based on the modal matching method. According to the investigation, the size of the slot can affect the angular distribution of radiation energy very obviously. If we want to study the THz radiation source using this grating, the parameters should be chosen cautiously.At the same time, the SPR from the rectangular grating is investigated in PIC simulation in this dissertation. In term of the simulation result, the SPR happens first for the single bunch. Then coherent emission of the evanscent wave occurs. If we keep the total charge of bunch fixed, the radiation intensity become smaller with the increase of the bunch's size. It is consistent with the theory analysis. For the periodic bunches, the radiation intensity can be enhanced when the SPR frequency equals to the frequency of the high order harmonious wave and its value is much bigger than other frequency. The amplitude of FFT transform to radiation energy grows in proportion to the square of the bunch's number. It also consists with the theory calculation.According to this dissertation's investigation, the grating's profile should be chosen cautiously to study the THz radiation source using SPR. The parameters of the grating and bunches should also be optimized.It is a good reference for further development on THz technology in our country.