Characterization of Coherent Radiation on Electron Bunch Compressor

Abstract

Coherent radiation is being used in various fields such as imaging, diagnosis, inspection, etc. In the magnetic electron bunch compressor, coherent radiation occurs when electron bunches are bent by a dipole magnet and electron bunches pass through the edge of the magnetic field. This thesis shows the measurement of the electron bunch length, and microbunhching instability using this coherent radiation. The femtosecond (fs) terahertz (THz) beamline of Pohang Accelerator Laboratory (PAL) is providing a THz radiation with a pulse energy of 7μJ by means of coherent transition radiation (CTR) from 65-MeV electron beams. The fs-THz beamline is dedicated to the users, therefore we need to provide a stable radiation for beamline experiments. For this purpose, the thesis shows the improvement of the electron bunch-length measurement and the RF phase feedback system to stabilize the intensity of THz radiation. The microbunching instability is an important issue for X-ray Free Electron Laser (XFEL). The intensity of the FEL can be reduced significantly by the microbunching instability so that the laser heater is widely used to reduce it. In the X-ray Free Electron Laser of the Pohang Accelerator Laboratory (PAL-XFEL), to monitor the microbunching instability directly, a visible CCD camera is included into the coherent radiation monitor which uses a pyro-electric detector. The thesis shows the measurement of the microbunching instability and the optimization of the FEL lasing at the PAL-XFEL.