Study On Smith-Purcell Radiation From Sub-picosecond Electron Beam

Terahertz(THz)radiation refers to the electromagnetic wave whose frequency locates in the range of 0.1THz to 10 THz,just between the microwave and the infrared.THz radiation has been applied to numbers of fields,including biology,material science,medicine,environmental monitoring,and security.The applications of THz radiation need THz source.Developing a high-intensity,tunable and stable THz source,thus,becomes a hot topic in recent decades.Sub-picosecond electron beam from accelerators can produce THz radiation through Smith-Purcell effect,which is a pretty stable and potential THz source.In this thesis,THz Smith-Purcell radiation generated from the interaction between a sub-picosecond relativistic electron beam and a metallic grating is studied in theory,simulation and experiment.First,the theory on the radiation from relativistic electron beams is discussed and the theoretical equations on the Smith-Purcell radiation are deducted.Second,the simulation on the interaction between a single bunch /bunch trains and a blazed grating/grooved grating to produce Smith-Purcell radiation is carried out.The results suggest that when driven by a single bunch,the radiation intensity from the blazed grating reaches its maximum at the observation angle two times larger than the blazed angle.What's more,the total radiation is stronger if the blazed angle of the grating is larger.For the grooved grating,there are peaks and valleys in the angular intensity distribution.The deeper the grooves are,the stronger the Smith-Purcell radiation is.When driven by bunch trains,the frequency coinciding with the bunch train spacing will be selectively excited.In a certain observation angle,the first order of Smith-Purcell radiation can dominate,and in another angle,the second order can dominate.At last,experiments on the Smith-Purcell radiation from sub-picosecond electron beams passing by the blazed grating are carried out at the accelerator facility of Tsinghua University.The THz radiation generated is detected by a bolometer,and the spectrum is measured by a Michelson interferometer.The spectrum,the relationship between the radiation intensity and beam-grating separation,the relationship between the radiation intensity and bunch length,and relationship between radiation intensity and beam charge are obtained.This work is of great significance in developing THz radiation source based on ultra-short relativistic electron beams.The simulation and experimental results contribute much in further understanding and research on THz Smith-Purcell radiation.