Research On Small Period Permanent Magnet Staggered Undulator

Accelerator-based light sources(including synchrotron radiation and free electron lasers)can produce artificial light with excellent quality,which is important and widely used in contemporary scientific research.However,accelerator-based light sources are generally large-scale and expensive.The undulator is one of the most important devices in accelerator-based light source.Reducing the undulator period length helps to reduce the scale of accelerator-based light source.Much work has been done to reduce the undulator period length,but the undulator period length still has bottlenecks near 10 mm.The solenoid-derived undulator can reduce the period length to 10 mm,but its superconducting solenoid limits the application.In this paper,permanent magnet magnetic circuit was used instead of superconducting solenoid to generate longitudinal magnetic field.A new mini-period permanent magnet staggered undulator was proposed.This undulator will work at room temperature,so its manufacture and application will be greatly simplified.In this paper,the following four tasks were carried out with the center of the mini-period permanent magnet staggered undulator.(1)The magnetic circuit of mini-period permanent magnet staggered undulator was designed,which can be divided into permanent magnet circuit and soft magnetic circuit.The analytical expressions of permanent magnet circuit and soft magnetic circuit were obtained respectively.The magnetic field calculation model of the magnetic circuit and the multi-objective genetic algorithm model were established.The optimization calculation of the mini-period permanent magnet staggered undulator was carried out,and the optimized magnetic field distribution was analyzed.The method of adjusting the magnetic field of mini-period permanent magnet staggered undulator was studied.(2)The test bench of small-period permanent magnet staggered undulator was built.According to the measurement requirement of small-period permanent magnet staggered undulator,the magnetic field measurment bench had been upgraded.The magnetic field of small-period permanent magnet staggered undulator was measured using magnetic field measurment bench.Although the longitudinal magnetic field and period magnetic field were different from the simulation results,the main reason was the errors of test bench,so the optimization results were basically verified.By measuring the relationship between period magnetic field and magnetic pole gap,the method of adjusting magnetic field through magnetic pole gap was also verified.(3)The best shimming method for small-period permanent magnet staggered undulator was determined.The multi-objective genetic algorithm was applied to the calculation of shim of small-period permanent magnet staggered undulator.Taking the electron trajectory deviation and peak-to-peak error under different magnetic pole gap as the objective variables,the calculation model of shim was established and the shim was calculated.After shimming,the magnetic field quality of mini-period permanent magnet staggered undulator has been greatly improved.Based on the fact that the saturation magnetization of temperature compensation alloy near room temperature is very sensitive to temperature,a passive compensation mechanism for temperature stability of permanent magnet undulator was proposed,and the compensation conditions were deduced.The compensation methods considering only the influence of temperature on permanent magnet materials,and both the influence of temperature on permanent magnet materials and the influence of temperature on the gap were studied,respectively.(4)By designing a SASE-XFEL facility and calculating its radiation performance,the capability of small-period permanent magnet staggered undulator in reducing the scale of SASE-XFEL facility was demonstrated.Finally,differing wth ordinary undulator,the small-period permanent magnet staggered undulator has uniform longitudinal magnetic field,so the possible influence of longitudinal magnetic field was also studied.