Theory And Simulation Of High-quality Ion Beams From Ultra-intense Laser Plasma Interaction

With the advances in ultra-intense ultra-short laser technology, novel table-top charged-particle accelerators and radiation sources based on laser plasma interactions have been attracting great interest due to their wide and novel applications. This thesis is focused mainly on the theoretical study and numerical simulation of the generation of high-quality ion bunches from ultra-intense laser plasma interaction. It consists of two parts:a relativis-tic Particle-In-Cell (PIC) simulation code for laser-plasma interaction, and the generation of high-quality ion bunches by ultra-intense laser irradiating on thin foil.To more conveniently and efficiently simulate laser-plasma interactions and to carry out investigation of new concepts in ion acceleration, we have developed our two-dimensional (2D) parallel PIC code based on the well-known simulation code LAPINE. The first part of this thesis is a detailed introduction of our code, which incorporates several advanced nu-merical methods. The PIC code is found to perform efficiently for simulating laser-plasma interactions.The second part of the thesis consists of three elements:(1) Using our2D PIC code, we propose a multistage acceleration scheme in which the Radiation Pressure Acceleration (RPA) and Target Normal Sheath Acceleration (TNSA) mechanisms operate in different stages of the foil acceleration process. In order to obtain a highly monoenergetic high-energy proton bunch, we use a thin double-layer target con-sisting of heavy ions and protons. The latter are first accelerated as a whole under stable RPA. At later times, the protons with their high charge-to-mass ratio are located at the rear side of the moving target and are thus subject to TNSA by the sheath electrostatic field. The compact and quasimonoenergetic qualities of the proton bunch are maintained. Gen-eration of quasimonoenergetic GeV proton bunches with this scheme is confirmed by2D PIC simulations. The resulting proton bunch can propagate for a very long distance while maintaining its good qualities, and should thus be useful in many practical applications. (2) Using2D PIC simulations, we show that adding a homogenous low-density back-ground plasma behind the thin foil target can improve the qualities of accelerated ion bunch. In particular, it is found that the low-density background plasma provides favorable modulation of the ion density and cooling of the thermal electrons in the target, and thus suppresses the deformation of the accelerated plasma as well as the subsequent thermal expansion. Our results show that the enter center region of the thin foil can be accelerated as a compact high-energy high-density quasimonoenergetic ion bunch at high laser energy conversion efficiency. We also propose an analytical model based on a modified light-sail mechanism for the process. The model can be useful for tailoring the physical parameters of future experiments and applications.(3) A complex target configuration aimed at generating high quality proton bunch by circularly polarized laser pulses at intensities of1020-21W/cm2is proposed. Two-Dimensional Particle-In-Cell simulations are carried out, which show that hundreds MeV high quality proton beam can be well produced. It is found that the collimation and mono-energetic qualities of the accelerated proton bunch from the frontal shaped thin foil tar-get could be greatly enhanced under the favorable modulation of a back inhomogeneous plasma layer. Three main mechanisms to improve the accelerated protons are found and discussed in detail, including transparency prevention, hole-boring acceleration and Debye shielding. Theories for tailoring the complex target parameters are also presented.