Measurement of Picosecond Electron Beam Length with RF Zero-phasing Method

In this paper, the electron beam length of China Academy of Engineering Physics THz Free Electron Laser (CTFEL) was measured by the means of the RF zero-phasing method. The downstream cavity of the 2×4-cell superconducting accelerator was used as the zero-phasing cavity. Then the electron beam length accelerated by the first superconducting cavity was measured, which was proved to be almost the same as the one at downstream cavity when the two cavities were both working, by the means of dynamics simulation. The measurement results show that the FWHM of electron beam is less than 6.8 ps after the acceleration of the 2×4-cell superconducting accelerator, which meets the requirement of the facility.