The simulation of beam arrival time jitter of THz source based on superconducting accelerators

China Academy of Engineering Physics Terahertz Free Electron Laser (CAEP THz FEL, CTFEL) is the first high-average power free electron laser terahertz user source based on superconducting accelerators in China. It has some characteristics such as high repetition (54.167MHz), high average power (>10W), and continuously adjustable frequency (0.7THz to 4.2THz). One of the critical issues of the user THz source is the time jitter. The jitter of the electron beam arrival time has a massive influence on the total time jitter in the experimental station. In order to study the ultrafast dynamic process in CTFEL with some techniques, such as pump-probe, SNOM, and single-pulse detection, an accurate beam arrival time jitter analysis in the beam line is needed. A program named a space charge tracking algorithm (ASTRA) is used to simulate the electron beam dynamic and calculate the beam arrival time at the entrance of the undulator in CTFEL. All the parameters in the simulation are from the experimental data of the facility. The simulation results show that the RMS arrival time jitter before the optical cavity is about 728 fs, and the significant contribution to arrival time jitter is the amplitude fluctuation of RF fields of two boosters in the superconducting accelerators, more than 95%.