Proton Accelerated Simulation Study Of The Interaction Between Ultra-strong Laser And Solid Target

Development of laser technology is promoted by the appearance of chirped-pulse amplification.With the realization of ultra-intense ultra-short laser pulse,researches of novel charged-particle accelerator based on laser plasma interactions have become more and more important.The laser-accelerated proton beams have been used in many related fields like medical therapy,particle radiography and inertial confinement fusion because of its unique characteristics,which broadens the scope of physics to a great extent.In the meanwhile,these developing applications put forward more requests about the laser proton acceleration,like higher proton energy and laser conversion efficiency and better beam collimation.Therefore,how to improve the proton beam qualities becomes one of the main challenges facing the laser proton acceleration at present.This thesis focuses on the numerical simulations of enhancement of proton qualities generated from ultra-intense laser plasma interactions by several different schemes.At the beginning of the thesis,we simply introduced the background and applications of laser plasma interactions,after which we gave a detailed presentation of theories about laser particle accelerations.In the third chapter,the fundamental of particle simulation method which is regarded as the third main method except experiment and theoretical analysis for plasma research was shown.At last and most importantly,we proposed two schemes for laser proton acceleration and simulated to analyze their availabilities.The first scheme is for confinement of proton beam divergence.According to earlier researches,when the proton beam produced by TNSA scheme is accelerated by longitudinal sheath field,it can experience the transverse thermal pressure of hot electron cloud at the backside of the target so that the beam will expand transversely in space leading to large divergence.We proposed a new channel target with the channel diameter a little larger than the laser spot and almost corresponding to proton source size to control the space spread of proton beams using the transversely electrostatic field along the inner walls of the channel generated by the hot electrons.The simulation results indicate that for the channel target,the proton beam has a better collimation with conserving the proton energy.The other aims at enhancement of maximum proton energy and laser energy efficiency.During the interaction of ultra-intense laser with solid target,the laser pulse accelerates protons indirectly by coupling energy to electrons,which create a charge-separation electric field at the rear side of the target working on the protons.The proton energy depends essentially on the hot electron temperature and density profile at the rear surface.In this thesis,a new cone-hole target is introduced,where the incident laser pulse is focused by the cone structure and then enters the central hole bored through the cone tip longitudinally keeping interacting with plasmas,which can enlarge the interacting area leading to more laser energy absorption.The simulations show that comparing to the foil target,the proton energy and laser coupling from cone-hoe target are both enhanced significantly.In addition,we also carried out a series of simulations to study the effect of the parameter of cone-hole structure and laser intensity on proton energy,and we found that there was a scaling law between the maximum proton energy and laser intensity in the interaction of short intense laser pulse with the cone-hole target.When increasing the laser intensity to a certain value,energetic protons over 100 MeV can be achieved.