Research On Field Integral Adjustment And Fast Measurement Method Of The Undulator In HUST THz-FEL

Terahertz technology is estimated as one of the top ten technology that changes the world. It plays a very important role on research fields covering medicine, national security, environmental monitoring and material inspection. Free electron laser is the most effective way to obtain high-power THz wave, while the undulator is one of the core devices of the free electron laser, which provides an environment for electronic and optical field coupling. Under the background of this research, the study of undulator, mainly includes the undulator magnetic field integral calibration and measurement are described.The first and the second field integrals of the undulator will influence the electron beam through the undulator, respectively, causing the angle deflection and position deviation of the electron beam, which need to be controlled within the acceptable range. Undulator model is established by using Radia software and the first and the second integrals error are adjusted by using magnetic block end adjustment and the correction coil. Magnetic end adjustment adjusts the height, gap and the thickness of the magnets for a given magnetic block structure, looking for the relationship about the integral to find the optimal value to meet the conditions. The undulator integral is corrected by adjusting the applied current of the correction coil, the relationship between the undulator magnetic integral and the applied current is studied to find the optimal one. Finally, the integral of the undulator magnetic field is measured by the platform based on the stretch-wire method. Then the first integral and the second integral can be obtained by using the relationship between the measurement data and the magnetic integral. And the influence factors are analyzed in the process of measurement. The platform also applies to measure the magnetic integral of undulator with 30 periods in THz devices.Magnetic blocks end adjustment and correction coil method have a good effect in the undulator integral error correction, and can basically eliminate the error within the tolenrece required by the FEL system. Also, the correction coil method can be operated remotely; Stretch-wire method has better accuracy of measurement, the repeatability of the first integral and the second field integral are less than 2.5?10^-6 T·m and 2.5×10^-6 T·m2, respectively. They meet the requirement of measuring the undulator in HUST THz-FEL.