Acceleration And Radiation Of Externally Injected Electrons In Laser Wakefields Driven By A Laguerre-Gaussian Pulse

As the development of high-power laser and plasma physics,the interaction between high-power laser and plasma becomes a focus of physics researches in recent years.The acceleration gradient of the wakefield excited by a high power laser in plasma can be as high as100 GeV/m which is about three orders of magnitude higher than that of the conventional accelerator.Because of this huge acceleration gradient,the accelerator based on laser plasma wakefield has great potential to make tabletop electron and radiation sources and it has attracted worldwide attentions in the last few decades.These compact electron and radiation sources may have wide applications in physics,biology,and material sciences.The current thesis is aimed at a tunable compact radiation source based on wakefield excited by a Laguerre-Gaussian pulse.The thesis includes four parts:The first part introduces the fundamental knowledge of laser wakefield acceleration including different electron injection methods,relativistic or self-guidance of lasers,pre-plasma channel guidance and Particle-In-Cell simulations methods.The laser wakefield acceleration can accelerate electrons to GeV energy in centimeter distance.High quality electron beams could be obtained through different optimized electron injection methods.The relativistic self-guidance of lasers and pre-plasma channel guiding can prolong the effective propagation distance of laser.Moreover,the Particle-In-Cell(PIC)simulations can provide detailed studies on the interaction between laser and plasma.The second part introduces the X-ray sources driven by high power laser and a code used in our studies for radiation calculation,i.e.Virtual Detector for Synchrotron Radiation(VDSR).Compared with the traditional X-ray tube,the X-ray sources driven by high power laser have a lot of excellent characters,such as:high intensity,flexible tunability,compactness and so on.The X-ray sources driven by high power laser include K_?radiation source,Betatron radiation source and so on.The K_?radiation source is produced by the interaction between laser and solid targets.The Betatron radiation source is produced by the betatron motions of electrons in a laser driven wakefield.The third part introduces the development of lasers and several kinds of special laser modes including Laguerre-Gaussian laser and Bessel-Gaussian laser.We also introduce the properties of the non-diffraction and self-healing of Bessel laser.And the properties of Laguerre-Gaussian laser including orbital angular momentum.Lasers with these special characters make them widely used in many applications,such as optical trapping and optical communications.In the last part we have introduced our main work on the LG pulse driven wakefield acceleration and Betatron radiation.By using three-dimensional particle-in-cell simulations externally injected electron beam acceleration and radiation in donut-like wakefields driven by a Laguerre-Gaussian pulse have been investigated.Studies show that during the acceleration process,the total charge and azimuthal momenta of electrons can be stably maintained for a few hundreds of micrometers.Electrons experience low frequency spiral rotation and high frequency betatron oscillation,which leads to synchrotron-like radiation.And the radiation spectrum is mainly determined by the electrons'Betatron motion.The far field distribution of radiation intensity shows axial symmetry due to the uniform transverse injection and spiral rotation of electrons.So,our studies suggest a scheme for tunable radiation sources based on a compact LG laser plasma accelerator.