Numerical Study On Betatron Radiation Generation And Sheath Electric Field Probing In Laser Plasma Interactions

In the physics of intense field,the interactions between the ultra-intense laser and low-density plasmas can provide a new alternative for the next generation of high energy electron beam sources and high brightness radiation sources.Among them,the most representative applications are the electron acceleration and radiation generation in the laser plasma wakefield.In order to get an electron beam with higher energy,smaller energy spread,larger charge and brighter radiation,it is necessary to put forward new mechanisms and optimization methods for the electron acceleration and trapping process.At the same time,as another important composition of the intense field physics,the proton acceleration via the sheath electric field generated in the interactions of ultra-intense laser and over critical density plasmas,needs a detailed electric field detecting because of the limited diagnostic techniques.After analyzing the current injection and accelerating mechanism in the electron's wakefield acceleration together with the electric field probing techniques,three thesis are mainly studied by theoretical and numerical simulations as follows:1)In the interactions of a circularly polarized laser pulse with plasmas,our theoretical analyses proved that an external axial magnetic field can modulate the resonance between the trapped electron's betatron oscillation and the laser electric field.When the external magnetic field is applied in the opposite direction to the self-generated axial magnetic field,a stronger betatron resonance and laser direct acceleration would happen.This results in an increase to the trapped electron's energy and the radiated X ray.At the same time,because of the external radial Lorentz force introduce by the magnetic field,the electron trapping efficiency is also increased,which further improves the X ray radiation intensity.Numerical verification is also conducted.2)By analyzing the electron's trapping separatrix in a wakefield,it is found that the minimum energy needed for trapping is acquired at the transversal boundary of the wake.By PIC simulations,we studied the possibility of accelerating an low energy electron beam by the wakefield accelerator.It is found that,the wakefield accelerator can accelerate the MeV electron beam to a maximum energy of 158 MeV with the beam's transversal length about 1?m.At the same time,the accelerated electron beam has a low energy spread of 2.9%.The radiated soft X ray is also studied by numerical calculations.3)Our numerical simulations find that,by employing an energetic and divergent proton beam for the radiography of the intense localized sheath electric field,the trajectory crossings can be prevented and a linearized density perturbation can be obtained on the detector screen.Because of the cylindrical symmetry,the sheath electric field is three dimensionally reconstructed from the linearized proton density perturbation by the Abel inversion.The dislocation of the reconstructed field is also corrected.It is seen that,the reconstructed field is in a good coincidence with the original PIC simulated results.