Research On The Novel Injection Schemes In Laser Wake-field Electron Acceleration

With the development of pulse laser technology, electron acceleration driven by ultra-short ultra-intense laser pulses interacting with low-density plasma has achieved significant progress. Based on this principle, the novel tabletop-accelerator has been studied widely. Since “electron trap” is the most important phase of laser wake-field acceleration, one of the key problems is that how to improve the number of trapped electrons, how to reduce energy spread, etc.Our work is based on a new scheme named “electron bow-wave injection”(EBWI), which is proposed by Y. Y. Ma to enhance electron trap. In this paper, an optimized method with use of wave-shaped pulses is suggested to improve the number of trapped electrons. We investigate the practical reason to realize it by theoretical analysis and PIC simulations. The results are important and beneficial for the future experimental design of laser wake-field acceleration to obtain energetic electron beams with large charge quantity. The content of this paper is composed of three parts:Firstly, we introduce models of “bubble” in laser wake-field acceleration. This section introduces the bubble model of A. Pukhov and electron sheath model of W. Lu in blowout regime. We focus on the model of H. C. Wu, who considers bubble core fields as well bubble shape modification due to the nondepleted electrons inside the bubble, and provides a theoretical basis for the bubble acceleration process.Secondly, the effect of pulse transverse profile on electron bow-wave injection of electrons in laser wake-field acceleration is investigated. It is found that the transverse profile of incident laser has a significant effect on trapping of electrons. Compared with the Gaussian pulse, the super-Gaussian profile laser pulse can drive more energetic electrons of the electron bow-wave into the bubble with higher longitudinal injection velocity in the same conditions. At last, the total number of trapped electrons increases almost 5 times, and the quality of electron beam is also improved obviously.Thirdly, the effect of pulse temporal profile on electron injection and trapping in the electron bow-wave injection regime is investigated. It is found that a positive skew pulse can enhance the wake-field amplitude, extend the accelerating aera, and improve the initial velocity of electrons injected into the bubble. Thus, more energetic electrons are driven into the bubble accelerating phase. The total injection number for a positive skew pulse is higher than those of negative skew and usual Gaussian pulses in the same conditions, and the quality of electron beam is also improved.