Design Of A Soft X-ray Free Electron Laser And Studies On Related Physics

FEL is becoming more and more important as a modern scientific research toolfor its unique characteristics, such as high power, short wavelength, coherent radiationand adjustable wavelength. As the first hard x-ray FEL facility in the world, LCLShas been successfully built, installed and commissioned, and now in user experimentphase. The unprecedented success of LCLS proved to the world the maturity of theoryand simulation tools, and it also drew people's attention to the future plan of LCLS.Under these circumstances, we started our work of studying the feasibility of usingA-Line as the soft x-ay FEL.We first systematically studied the feasibility of using A-Line as the soft x-ray freeelectron laser beam line. We designed a new A-Line beam transport system, analyzedthe impact on the beam quality of different physical effects, such as the incoherent andcoherent synchrotron radiation. The results demonstrated that using A-Line as the softx-ray FEL beam line is viable and theoretically proved that LCLS could run hard andsoft x-ray simultaneously.The polarization control of soft x-ray FELs is one of the most interesting topics inthe FEL field. We studied polarization control with the crossed undulator and RF undu-lator scheme, respectively. We analyzed the polarization control efficiency in SASE andSeeded FEL modes with the crossed undulator, and gave the explanation for the degra-dation of the polarization control efficiency. We proposed a new polarization scheme,which could provide a higher degree of circular polarization at second harmonic. Wealso comprehensively analyzed the power need for the radio frequency undulator.Undulator period is very difficult to be fabricated to less than cm level confined bythe machining technique. Therefore, making good use of the harmonic radiation in aplanar undulator becomes an efficient method to reduce the radiation wavelength. Westudied and analyzed a modified undulator configuration. The magnetic field and itsimpacts on the radiation spectrum were also computed .