Measurement and Optimization of Undulator for a THz-Band FEL Oscillator

FEL (Free Electron Laser) Oscillator is a important candidate of powerful, tunable and narrow-band THz sources. A classical FEL oscillator generates THz wave through electron wiggling motion in undulator. CTFEL, a THz FEL oscillator at CAEP (China Academy of Engineering Physics), also has been equipped with a Halbach-type undulator. Because of the significant influence on FEL performances, magnetic field of undulator must be measured and optimized before installation. The longitudinal and transverse distribution of magnetic field were scanned and optimized. Electron trajectory, peak-to-peak error and phase error were calculated based on the longitudinal distribution of magnetic field, while good field region was obtained from transverse distribution of magnetic field. All of the above parameters had been adjusted to satisfy the requirements. In this proceeding, the measurement results were presented and discussed in detail.