Design,measurement and optimization of undulator for terahertz free electron laser

Abstract

Electron trajectory center deviation and magnetic field errors of undulator have a great influence on the performances of CTFEL facility, which were limited in the range of specification requirements by preliminary design and post measurement and optimization. In the preliminary design, the global system errors were avoided as far as possible: the magnetic structure has a planar anti-symmetric structure to ensure the coincidence of electron trajectory center and undulator magnetic axis; the special design of magnetic structure end weakens the influence of gap on second integral of magnetic field at undulator exit; the beam and frame of the mechanical system have good rigidity and the control system with close-loop configure guarantees high accuracy of the gap control, all of which limit the magnetic field errors caused by the gap inconsistency. The residual global system errors and local random errors of the magnetic field were reduced in the later measurement and optimization: the longitudinal and transverse distributions of magnetic field were measured using magnetic field measurement bench and then the undulator field was shimmed and optimized by adjusting the positions of standard unit components. Finally, the electron trajectory center deviation, peak-to-peak error, phase error and good field range error meet the requirements of specification after optimization.