Researches On PIC Algorithms And Physics Of Laser-Matters Interactions

This thesis has introduced some basic laser-plasma interaction mechanisms and Particle-in-Cell( PIC) method. High-order interpolation algorithms for charge conversion in PIC method have been developed. Second-order and third-order which can be expanded to any even-order and odd-order have been presented in detail. Test simulations have been carried out, demonstrated the advantages of high-order algorithms in enhancing computation precision, enlarging the grid sizes and reducing the CPU time.This thesis has investigated the generation and heating mechanisms of hot electron in the interaction between laser and nanolayer target, proposed conical nanolayer target(CNT) to enhance energy conversion from laser to hot electron. With PIC simulations, it is found that the energy conversion can be enhanced by more than one times comparing with common nanolayer target. Meanwhile, hot electrons can be well collimated in the CNT, which shows the possible application in fast ignition of ICF.This thesis has studied the target normal sheath acceleration(TNSA) in detail. Employ Coulomb explosion model to explain the influence of proton layer initial sizes on proton bunch parameters. Nanobrush target and conical nanobrush target have been proposed to enhance proton beam energy conversion, demonstrated by two-dimensional PIC simulations. To improve spatial resolution of proton radiography, this thesis proposed a cone-top-end target to generate proton point source.This thesis has investigated the effects of laser duration, laser intensity and plasma density on proton bunch energy, proton number and energy conversion in Hole-boring Radiation Proton Acceleration(HB-RPA). The difference between the proton energy from simulations and scaling equation has been discussed. It is found that laser duration of 15~20fs is the optimal duration for achieving higher energy conversion. Three-dimensional HB-RPA simulations have been carried out for the first time. It is found that the laser intensity is significantly enhanced via geometric focusing and other multidimensional effects as the plasma deforms, resulting in ion energies exceeding 1D predications. An ultra-short proton bunch of 4×1010 can be accelerated to energy >1.3GeV, △E/E < 28%, by using a 15 fs laser of 8.0×1022Wcm-2. The transverse emittance is less than 0.067mm-mrad and the spread angle is about 9.5°. Proton energy above 1.74 GeV, energy conversion up to 11.7%, and bunch size less than 1μm can be accelerated by optimizing the laser and plasma parameters.This thesis has reported the acceleration of ultra-short electron bunch and gamma bunch driven by high intensity short laser pulse. Theoretical model to generate ultra-short bunch basing on next generation laser system has been discussed, which have been confirmed by numerical simulations. The effects of laser duration and intensity on the qualities of electron bunch and gamma ray bunch have been considered in detail.