The System Design And Novel Theoretical Research For Soft X-ray Self-seeding Free Electron Laser

In recent years,high gain free electron laser(FEL)aims to provide high intensity,ultra-short pulse length and high repetition,full coherent X-ray,which makes FEL much more widely used in scientific frontiers such as biology,materials,medicine,energy even environment etc.Self-amplified self-emission(SASE)has been the primary consideration for most FEL facility under construction,which is also beeen proved to be a feasible scheme to obtain high intensity,short wavelength and transverse coherence FEL pulse.However,SASE radiation pulse generates from the amplification of initial shotnoise in the electron beam,which induces the SASE radiation holds the inferior features,for example,poor longitudinal coherence,relative wider bandwidth and pulse jitter.To get full coherent X-ray FEL radiation,amounts of schemes are put forward,in which harmonic generation combined with external seeding schemes such as high harmonic generation(HGHG)and eco-enable harmonic generation(EEHG)are proved to be workable schemes to generate full coherent FEL pulse,but these schemes are limited to the modulation depth,the radiation wavelength is limited to be longer than 4nm.Self-seeding FEL is firstly proposed to improve the longitudinal coherence of SASE FEL and generate relative narrower bandwidth FEL pulse.Soft X-ray self-seeding results,demonstrated in LCLS,show that soft X-ray self-seeding still have many problems to be solved.The soft X-ray self-seeding is the basic operation mode of shanghai high repetition rate XFEL and extreme light source(SHINE)to generate full coherent X-ray.In this dissertation,we focus on the research of physical and system design based on SHINE as well as shanghai soft X-ray FEL user facility(SXFEL user facility),and we also proposed a series new operation modes to solve the problems exiting in soft X-ray self-seeding schemes.In the novel theoretical research,we proposed a series of new methods to solve the problems exiting in soft X-ray self-seeding scheme: reversed taper undulator is used to obtain the the electron beam with harmonic bunching signal,which can generate harmonic radiation in the following undulator,the photon energy gap between the hard and soft X-ray self-seeding is compensated by our proposed method according to the simulations;We prove the inducement of the sideband in the soft X-ray self-seeding is the microbunching instability by theoretical study and 3D simulations,and a phase mixing is considered to suppress sideband bunching signal in the electron beam,thus suppressing even eliminating the sideband in the self-seeding radiation,we also prove that our proposed method is feasible to suppress the sideband in soft X-ray self-seeding scheme according to 3D simulations;Finally,we propose a new working scheme to obtain multi-color soft X-ray radiation pulses in FELs based on conventional self-seeding scheme,the monochromator with thin foil blocks is adopted to obtain a multi-color coherent optical wakefield.3D self-seeding and wave optical wave optics propagation simulations are carried out to confirm our proposed method,and the simulation results show that the proposed method is feasible to provide multi-color FEL radiation pulse.In the physical design,an integrated soft X-ray self-seeding design based on SXFEL user facility and SHINE is presented.The final self-seeding FEL output is calculated by the simulation,the undulator layout is also designed based on the FEL simulation results.Self-seeding simulations using the electron beam parameters of SHINE with different photon energy are carried out to obtain the FEL radiation characteristics.Based on the simulation,we perform the optimization about the optical and physical parameters and present the design requirement of the monochromator system.In the optical design,we give optical system design based on the SHINE,and the chicane system designs are also presented according to the optical design.After that,we trace the optical pulse and perform the analyses about the optical elements.In this dissertation,we display complete physical and optical designs,the design is the first design of soft X-ray self-seeding system in china,it can cover the photon energy of 0.4-1.5keV and fill the requirements of SXFEL user facility and SHINE at the same time.Moreover,we also consider the requirement of high repetition.