Generating Ultra-high Quality Electron Beams In Plasma-based Acceleration

The advanced acceleration technology based on the plasma wakefield has experi-enced tremendous progress in the last decade,which is promising to revolutionize the applications of laser and accelerator technology.One of the key challenges for the plasma-based acceleration?PBA?is how to controllably generate the high quality electron beams largely exceeding those the current accelerator techniques can achieve.The thesis carries out indepth study on this issue.By systematically teasing out the general rules of the injection,the ionization injection and the plasma density modulation injection are deeply studied,and the novel schemes for generating the ultra-high quality electron beams effectively are proposed.Such schemes can boost the beam brightness by 3 to 6 orders of magnitude compared to the current techniques.Once verified experimentally,it will produce important influence on the development of the future lightsource and the linear collider technologies.The thesis also establishes a novel particle-in-cell?PIC?algorithm with high computing efficiency and low noise,offering a powerful tool for simulating the proposed injection schemes.In addition,the issue of measuring ultra-low emittance is dicussed in detail and a feasible method is verified,which sets the foundation for the related experiments in the future.Overviews for each chapter are listed below:In Chapter 2,the general rules for the electron injection in PBA are analyzed system-atically.The basic ideas of generating high quality electron beams are proposed.In Chapter 3,based on the detailed analysis of the ionization injection,a novel scheme of achieving the injection by transverse colliding lasers in a beam-driven wakefield is proposed.Simulations show this scheme can generate electron beams with ultra-low emittance?<10 nm?,low slice energy spread??10 keV?and ultra-high brightness(>10¹⁹A m^-2rad^-2,3 orders of magnitude higher than the current techniques).In Chapter 4,the possibility of generating ultra-high quality electron beams through the density modulation injection in the blowout regime is discussed systematically.By deeply analyzing the electrons'motion during the injection,three-dimensional kinetic model is established and the key to increasing the beam brightness is discovered.Simula-tions further verify the scheme has the capability to generate electron beams with ultra-low emittance??10 nm?,high current?>10 kA?,low slice energy spread?<1 MeV?and ultra-high brightness(>10¹⁹A m^-2rad^-2).Meanwhile,motivated by the physical simi-larity of this scheme,the cascading injection scheme is proposed,which can further boost the beam brightness by 2 to 3 orders of magnitude.In Chapter 5,a new PIC algorithm with high parallelization and low numerical noise is decribed.The algorithm can eliminate the numerical Cerenkov instability in the current PIC simulations effectively,providing a powerful tool for studying the high quality injection.In Chapter 6,the indepth discussion on the issue of measuring ultra-low emittance is conducted.Focusing on the high-gradient permanent magnetic quadrupole?HGPMQ?method,the error and reliability analyses are systematically carried out,confirming its potential for measuring ultra-low emittance?<0.1?m?.Experimental system with 50nm emittance resolution is designed and fabricated and the measurement of?m level emittance is preliminarily realized,which lays the foundation for the future experiments of the ultra-low emittance measurement.