Study on a Polarization Controllable Undulator for High-Gain Free Electron Lasers

SASE FEL can generate intense and coherent linearly-polarized X-ray when high energy electron beams travelling through a long planar undulator. It is also of great importance and interest to control the polarization of FEL. One possible solution is utilizing a customized undulator to adjust the magnetic field direction. By tuning the displacement of the magnetic block arrangement, variation of polarization could be achieved. In this paper we study on a polarization controllable undulator to realize the variable polarized magnetic field. Different shapes and design considerations of the magnetic block configuration will be introduced. The value of peak field and the region of good field will be analysed and discussed.