Theory And Application Studies On The Electron Beam Based Polarization Radiation

In this thesis, two types of electron beam based polarization radiation are stud-ied:the Cherenkov wakefield radiation excited by an electron beam passes though the cylindrically symmetric dielectric-loaded waveguide (DLW) and the Smith-Purcell ra-diation (SPR) emitted when an electron beam passes close to the surface of a metallic grating. The DLW structure is capable of efficient energy exchange with the beam in a compact size, and thus finding use in an increasingly wide variety of applications, such as generating microwave and THz sources and manipulating electron beam longi-tudinal phase space. SPR, which is characterized by a broad range of frequencies, has promising applications centred on its use as a compact, tunable high-power source of electromagnetic (EM) radiation and as a diagnostic tool for the determination of the lon-gitudinal (time) profile of electron beams. We will focus on the theory and application studies on the two types of polarization radiation, and because of growing demand to develop terahertz radiation sources in many areas of science and technology, the most major study is THz radiation generation.In the aspect of Cherenkov wakefield, we propose three different compact schemes for generating narrow-band THz radiation. The first one is a compact narrow-band THz radiation source based on the photocathode rf gun, in which the subpicosecond electron bunch with relative high charge is generated directly in the gun and used to drive a small DLW tube for generating high-power radiation at the low end of the THz frequency. In the second scheme, an electron bunch train is initiated on the photocathode of a direct current (DC) gun by a laser pulse train, subsequently accelerated by the adjustable high voltage and applied to selectively excite one of the eigenmodes in the DLW structure. This proposed source has the advantages of compact, robust and relatively high pow-er. In the third scheme, we propose to generate high power THz radiation during the Cherenkov free electron laser (CFEL) process driven by DC electron beam with har-monics generation method. By properly choosing the parameters, the high-order modes can be the harmonics of the fundamental one, thus high frequencies radiation corre-sponding to high-order modes will benefit from the dominating bunching process at the fundamental eigenfrequency and can also be coherently excited. With the proposed method, high power THz radiation can be obtained with a easily achievable electron beam and a large size DLW structure. In addition to the THz radiation, we propose a novel method to measure the electron bunch length with a dielectric wakefield radia-tion (DWR) decelerator. When an electron beam passes through a DLW, the DWR is excited leading to an energy loss of the electron beam which is largely dependent on the electron bunch length and can be easily measured by an electron spectrometer. The features of the proposed method are:high resolution for electron bunches with high peak currents, reasonably simple and low cost (consider that the electron spectrometer is essential for a normal accelerator facility).In the aspect of SPR, we propose another compact narrow-band THz radiation source, in which the SPR is enhanced by resonance overlapping. The spectrum radi-ated by one single electron from the lamellar grating with a narrow groove can have high-density narrow-band peak feature and this phenomenon is studied by analytical theory. A photocathode rf gun can generate trains of electron bunches with relative-ly high charges and ultrashort microbunch lengthes by illuminating the cathode with trains of laser pulses whose transverse sizes are expanded in order to restrain the space charge forces. By properly choosing the parameters, the peak frequency of one-electron radiation can be overlapped with the repetition frequency of the electron bunch train, which will generate extremely high intense narrow-band THz radiation. In addition,the rigorous theoretical investigations on the SPR from nano-scale metallic rectangular and arbitrary-profile gratings respectively with surface plasmon polaritons (SPPs) taken in-to consideration are carried out, and the SPR from nano-scale metallic gratings has the promising applications such as tunable nano-scale light production and bunch-length diagnostics.