High-quality laser wakefield electron accelerator

Abstract

The acceleration gradient of laser wakefield acceleration is 3–4 orders of magnitude higher than that of state-of-the-art radio-frequency accelerators, which has unique advantages in the field of electron acceleration. With the development of application fields, higher requirements are put forward for the quality of electron beams. Achieving high stability, high energy, high charge, narrow pulse width and low emittance is the direction of long-term efforts in the field of electron acceleration. This article mainly summarizes the achievements of the relevant research teams in electron acceleration from Shanghai Institute of Optics and Fine Mechanics in recent years. The energy of the electron beam based on the acceleration of the laser wakefield is mainly limited by the dephasing length and the laser pumping loss length. Aiming at the problem that the two stages of laser wakefield acceleration cannot be controlled independently and the plasma density is difficult to balance, a cascaded acceleration scheme where the injection stage and the acceleration stage are separated is proposed. The injection stage has a higher plasma density and the acceleration stage has a lower plasma density. The acceleration stage with lower density has a longer dephasing length, so that a higher acceleration can be obtained without affecting electron injection. Finally, the electron beam energy of the order of GeV is obtained in experiment. In order to obtain a higher-quality electron beam, a low-energy-spread electron beam is obtained experimentally by using energy chirp controlling. The six-dimensional phase space brightness, which simultaneously characterizes multiple qualities such as electron beam emittance, charge and pulse width, is introduced. It is hard, with high quality only, to achieve long-distance transmission of electron beams and to generate free electron lasers. For the development of free electron lasers, the transmission and modulation of the electron beam are equally important. Taking into account the need to further optimize the acceleration of electrons from generation to realization of active control, higher quality and higher stability, it is necessary to monitor the interaction process between laser and plasma in time to obtain parameter through diagnosis. We have designed and optimized a variety of diagnostic solutions suitable for electron acceleration in the laser wakefield to achieve single-shot measurement of electron beams at different positions, such as using Betatron radiation inversion to measure ultra-low emittance. The effect of laser multifilament on the quality of the generated electron beam is also discussed.