Numerical Simulation Study Of Vacuum Laser Electron Acceleration Scheme Guided By Cone Target

With the advent of the chirped pulse amplification technology,the development of laser technology has been greatly promoted,and the laser output power has been continuously improved.The interaction between laser and matter has entered a new field.Among them,laser-accelerated high-energy-density collimated fast electron beam has many good characteristics and have been applied in many research fields,such as fast ignition inertia confinement fusion schemes,gamma ray imaging,and relativistic positron generation,expanding the field of physics research area.Therefore,how to efficiently generate a large amount of high-energy collimated fast electrons has always been a research hotspot in the field of intense laser-plasmas.In this paper,a two-dimensional PIC simulation method is used to study the vacuum electron acceleration of cone target driven by laser,aiming at the main problem that restricts the research and development of the vacuum acceleration mechanism:how to generate an electron with a certain initial velocity and inject it into the acceleration field has been improved.In the first part of the paper,the research background and research field of laser plasma interaction are introduced firstly.Then the basic theory and research status of laser electron acceleration are described in detail.Then the plasma particle simulation method is introduced.In the second part of the paper,the relativistic dynamics of a single electron in a plane wave laser field is studied.We solved the analytical general solution of the motion of electrons with initial momentum in a plane wave laser field and found that electrons with longitudinal initial momentum can gain greater energy during acceleration.On this basis,we have proposed a laser-driven cone target vacuum electron acceleration program.The third part uses the two-dimensional PIC simulation program OPIC to simulate the above scheme.We find that the laser interacts with the solid target at the entrance and generates a large amount of hyperthermal electrons along the direction of laser propagation by means of vacuum heating.These hyperthermal electron beams are captured by the longitudinal electric field of the Gaussian laser at the focal spot edge and get long-distance acceleration.At the same time,the cone structure can effectively enhance the laser intensity,and the solid density target wall can constrain the long-distance transmission of the laser in the vacuum chamber.In this acceleration scheme,the hyperthermal electrons undergo a millimeter-level vacuum acceleration under the action of a longitudinal acceleration electric field,and finally obtain a strong fast electron beam with an energy of GeV magnitude and divergence angle of about 1°.Among them,the electron energy with kinetic energy greater than 100 MeV reached 3 nC/μm.The electron beam generated by this electron acceleration scheme is suitable for gamma ray imaging etc,has a low requirement for uni-energy,but it has a demand for electricity,energy,and collimation.