Study On The Generation Mechanism Of The Longitudinal Coherent Radiation Based On Electron Storage Ring

The emergence of synchrotron radiation light source(SL)and free electron laser(FEL),had brought unprecedented revolutionary research tools for physics,chemistry,life science,material science and energy science,which had greatly promoted the development of related science.More than 40 Nobel prizes are directly related to the light source technologies and applications.SL has become one of the most important large-scale scientific platforms supporting multi-disciplinary basic and applied researches.SL has many advantages,such as wide spectrum coverage,high average brightness,stable pulse energy and simultaneous support for multiple users.SL which was born in the 1960s,has experienced three generations of development and evolution.Now it is on the journey of the fourth generation called as diffraction limited storage ring based light source,which has higher brightness and transverse coherence.Its average brightness can reach 10^21-22photons/s/mm²/mrad²/0.1%BW,however,the emittance of electron beam in such storage ring is close to the diffraction limit of the photons,and the improvement of brightness by reducing the electron beam transverse emittance is basically to the end.In the"post diffraction limit era",to further improve the performance of the light source is a common issue of SL scientists all over the world.Linac-based FEL has ultra-high peak brightness and ultra-short pulse structure.Its ultra-high peak brightness is from the longitudinal coherence produced by longitudinal micro-bunching effect of electron beam.If the advantages of storage ring and FEL can be combined,short wavelength with adjustable pulse length from 100 femtoseconds to tens of picoseconds,full coherent and high peak brightness radiation can be generated which can greatly enhance the performance of the SL,expand its application range,and meet the needs of most of the ultra-high energy resolution,ultra-fast experiments and nano-spacial-resolution experiments.Based on this background,it is proposed to use the FEL operation mechanism to introduce micro-bunching into the electron beam in the storage ring to produce longitudinal coherence,so that even if there is no high gain process,the radiance can be 2?6 orders of magnitude higher than the spontaneous emission generated by the undulator.The mechanism of FEL mainly classified to two categories:self-amplified spontaneous emission(SASE)and seeding laser scheme.Since the SASE FEL starts from electron beam shot noise,the output of SASE FEL typically has limited longitudinal coherence.Seeding laser schemes include high gain high gain harmonic generation(HGHG),echo-enabled harmonic generation(EEHG)and phase-merging enhanced harmonic generation(PEHG),et al.However,these schemes require large energy modulation amplitudes,which will introduce large energy spreads,degrade the quality of the electron beam in the storage ring,and seriously affect the normal operation of the storage ring.In this thesis,an advanced electron beam modulation method,angular dispersion enhanced microbunching(ADM)scheme,is used to generate longitudinal coherent radiation.This scheme makes full use of the advantage of ultra-low vertical emittance of storage ring.By manipulating the transverse and longitudinal phase space of electron beam,the small vertical angle divergence of electron beam is mapped to the longitudinal position of electron beam,resulting in micro-bunching of electron beam and emitting longitudinal coherent radiation.The major advantage of this scheme is that it only needs a very weak energy modulation amplitude to produce a strong high harmonics radiation,and the lattice structure of this scheme is pretty simple,which can be easily implemented in the storage ring.This thesis first introduces the physical mechanism of the ADM scheme,and creatively combines the ADM with the diffraction-limited storage ring to produce the fully coherent radiation with brightness of 10²⁴ photons/s/mm²/mrad²/0.1%BW at repetition rate of 10 k Hz.The brightness is two orders of magnitude greater than the diffraction-limited storage ring.At the same time,a variant of the ADM,the oblique incidence laser modulation scheme,is also studied.The characteristic of this scheme is that the oblique incidence seed laser interacts with the electron beam in the undulator to modulate both the energy and the vertical angle of the electron beam,which may produce the high harmonics radiation of the seed laser.In order to improve the harmonic conversion efficiency of the oblique incidence laser modulation scheme,a large beta function is needed.Considering the feasibility of this scheme,the bypass design is adopted which can solve the large beta function problem.In this thesis,the specific lattice structure of oblique incidence laser modulation scheme and the bypass lattice design are given.Finally,the research of the reversible steady-state microbunching(SSMB)is presented,which lays a foundation for the realization of reversible SSMB in the future.In summay,the research of this thesis shows out a feasible scenario for the development of the next generation of light sources,which may be an important candidate of the next generation of light sources.