Electron Acceleration And Radiation Based On Laser Plasma Wakefield

The emergence of particle accelerators is a milestone in the history of the development of human sciences.The development of particle accelerators has always represented the forefront of human beings' pursuit of physical essence and limits.In recent years,the development of laser technology,especially the advancement of ultra-short ultra-intense laser technology,has promoted the continuous development of high energy density physics in modern physics.An advanced accelerator concept has been discovered in the interaction between ultra-short ultra-intense laser and plasma: laser wakefield accelerator(LWFA).Compared to conventional accelerators,the electron acceleration gradient in LWFA can be up to three orders of magnitude higher,and can reduce current large-scale conventional accelerators up to several kilometers to table-top size,which is expected to be an alternative to the next generation of TeV energy level accelerators.The program also has the potential to miniaturize and particalize conventional synchrotron radiation devices that require high-energy electrons.However,the high-energy electron beams and radiation produced by LWFA still have some disadvantages compared to the conventional accelerators and radiation sources that are already mature,future research is still needed.In this thesis,we will give our own opinions on the electron acceleration and radiation generation processes based on LWFA,such as electron energy enhancement,electron injection mechanism,and radiation generation schemes.We hope to push LWFA to practical use.In addition to the introduction,this dissertation mainly includes the following two aspects.The first part mainly studies the electron acceleration process in LWFA.First,we will propose a new LWFA multistage coupling scheme.By using a curvature-graded curved plasma channel as a transition stage,we achieved a change in the propagation direction of the laser pulse and ensured the laser oscillation and the laser enveloping distortion were minimized when the new laser was transmitted in the next straight plasma channel.At the same time,when the electron beam is transmitted in the plasma,the focusing effect of the wake field on the electron beam is excited,and the scheme can achieve high-efficiency and high-stability cascade coupling.On the premise of guaranteeing the quality of the electron beam,the pre-accelerated electron beam is once again accelerated,laying the foundation for the future manufacture of TeV energy-grade laser wakefield accelerators and colliders.Next,we will study the boundary layer electrons in LWFA under the bubble regime.We observe that some electrons in the bubble boundary layer will obtain higher transverse momentum and exit from the wakefield laterally from both sides of the bubble.According to the difference in the separation position,we distinguish three boundary waves: the tail wave exiting the central axis at the sheath tail,the lateral wave exiting in the middle of the sheath parallel to the laser propagation direction,and the bow wave that emerges from the sheath head.The boundary wave will take a considerable proportion of energy from the wakefield,reducing the actual pump depletion distance.By studying dynamics of boundary layer electrons,we can suppress the formation of high-energy boundary layer electron waves by using a laser with relatively low intensity,large focal spot,and high plasma density,thereby improving the energy conversion efficiency.On this basis,we will also put forward our own opinions on how to apply the boundary layer electrons with certain energy.Finally,we will investigate the electron injection and acceleration under driving light and high relativistic intensity injected light.We have found that when the two beams have a certain time delay and cannot directly collide,a quasi-monoenergetic electron beam can still be obtained.After further analysis,we find there exists electron injection caused by wakefield collision under this condition,and the fine tuning of the delay will cause the charge of injected electrons change due to the different phase of the wakefield.Also,such electron injection mechanism has the potential to detect the structure of the wakefield as a novel diagnostic method.The second part focuses on the tunable electron radiation in LWFA.First,we study a compact all optical radiation source based on laser-plasma acceleration in a straight channel.With the laser pulse off-axially injected,its centroid oscillates transversely in the plasma channel.This results in a wiggler motion of the whole accelerating structure and the self-trapped electrons behind the laser pulse,leading to strong synchrotron-like radiations.Unlike the usual betatron trajectories,electron oscillations in our scheme have fixed period and amplitude.As long as the incident parameters of the laser and the parameters of the plasma channel are changed,the trajectory of the electron can be easily changed,thereby adjusting the radiation region and the radiation spectrum of the X-ray radiation.Next,we extend the above scheme to a more general three-dimensional situation through high-dimensional particle simulation,that is,the situation where the direction of the wave vector and the central axis of the plasma channel are different when the laser is incident.At this time,we found that the oscillating trajectory of the electrons would become a spiral and generate radiation in a hollow elliptical or circular area.Because the direction of the lateral velocity of the electrons in the spiral movement constantly changes,photons polarized in different directions are radiated.In simulations,we can obtain different polarized radiation at different positions on the radiation receiving surface,and we can also adjust the polarization direction of the radiation by changing the incident parameters of the laser.Finally,we studied the Thomson scattering of high-energy electron beams and scattered light with high relativistic intensities produced by LWFA,analyzed the causes of high-frequency radiation in the process,and calculated the order of radiation with respect to the fundamental scattered laser.In addition,we successfully explained the far-field diamond radiation distribution observed in the experiment through numerical simulation.The radiation spectrum and radiation power obtained in the simulation are in good agreement with theoretical calculations and experimental results.