Research On Integral Field Optimization Method Of Pure Permanent Magnet Phase Shifter In SXFEL

By the magnetic field optimization of five pure permanent magnet phase shifters in Shanghai soft X-ray free electron laser(SXFEL)device in this paper,we establish a method to optimize the permutation of permanent magnetic blocks on several phase shifters at the same time.After the optimization,the first integral of the magnetic field generated by each phase shifter in the beam direction can achieve a minimum.We also propose a complete method to shimming the integral field of pure permanent magnet phase shifter,which provides a good theoretical guidance and technical preparation for the development of pure permanent magnet phase shifter.In this paper,the first chapter introduces the development of the free electron laser and requirements of the undulators in free electron laser device.Then,the main types of phase shifter,the geometrical structure of pure permanent magnet phase shifter in Shanghai soft X-ray free electron laser device and the permanent magnet block and phase shifter magnetic field measurement method are briefly presented.The second chapter mainly introduces the basic motion law of the charged particles in phase shifter,the working principle of the phase shifter and how to calculate the integral of the magnetic field with the surface magnetic charge method.In the third chapter,we introduce the optimized sequencing scheme of the permanent magnet block on permanent magnet phase shifter.Because of the large number of permanent magnet blocks,we choose the permanent magnet block in the beginning.The required number of permanent magnet blocks are selected according to the discretization of the magnetization of each block and the magnetization deflection angle.Then,the simulated annealing algorithm is used to optimize the permutation of permanent magnet blocks of the five phase shifters at the same time,and the optimization results under two different order optimization objective functions are compared.Chapter 4 introduces the shimming method and shimming results of first integral field of the four phase shifter.Firstly,the calculation formula for the first integral field of the phase shift caused by the change of the height or rotation angle of the single block is derived.Then,according to the measurement results of the first integral field,The adjusting value of height or rotation angle of corresponding magnet block was calculated.Finally,the first integral field of shimmed phase shifter meets the engineering needs well.The fifth chapter analyzes the main sources of the error between the expected values of the integrated field and the actual measured values after optimization.Through the research of this paper,we successfully achieved the optimization of the permanent magnets and integral shimming field for five phase shifters.of the Shanghai soft X-ray free electron laser device.After field correction,the integral error of the phase shifter is less than 20 Gs.cm both in the center line for all gaps and horizontal position x < 2 mm at the minimum gap.