Research On The Generation Of Ultra-intense Laser-driven Intense Ion Beams And Its Propagation In Plasmas

Intense ion beams have an important research value in ion beam driven fast ignition,production of warm dense matter,cancer therapy,etc.The generation of intense ion beams in the interaction of laser and ultra-thin target and its propagation in plasmas are studied theoretically and numerically.The main structure of the dissertation is as follows:Firstly,the development of transverse instability in the radiation-pressure-acceleration dominant laser-foil interaction is examined.When a plane laser impinges on a foil with modulated surface,the transverse instability is incited,and periodic perturbations of the proton density develop.The growth rate of transverse instability is examined by using the Fourier analysis of the target areal density.It is found that the linear growth of the transverse instability lasts only a few laser periods and then gets saturated.In order to optimize the modulation wavelength of the target,a method of using information entropy is put forward to describe the chaos degree of the transverse instability.With appropriate modulation,the transverse instability shows a low chaos degree,and a quasi-monoenergetic proton beam is produced.Secondly,the mechanism of the acceleration and focusing of protons driven by laser triggered Coulomb explosion from a thin arched carbon-hydrogen target irradiated by a relativistic-intensity laser pulse is investigated.As an intense linearly polarized laser pulse impinges on the thin target,a considerable number of electrons are evacuated,leading to Coulomb explosion in the excess positive charges left behind.Accompanying with the acceleration,the protons are focused radially in the Coulomb field,which is mainly contributed by the carbon ions.An analytical model is proposed to predict the proton energy and the focal position,which is fairly consistent with simulations.It is demonstrated that a compact proton bunch with the highest density of?40n_cand energy density of?3×10¹⁷J/m³is obtained in 3D simulations with a laser with the intensity of 2.4×10²¹W/cm².In addition,the effects of laser and target parameters on the proton focusing driven by Coulomb explosion are investigated.It is found that a linear laser pulse contributes to the occurrence of the Coulomb explosion in a short time and a larger focal spot concerns the homogeneity of the induced Coulomb field.Meanwhile,the geometrical property of the arched target and the buffer action of carbon ions lead to the forward focused protons.Thirdly,the stopping power and the material resistivity of ion beam transport in partially ionized plasma are modeled.It is the first time that we implemented the BPS stopping power model of free electrons and the modified Bethe stopping power model of bound electrons in the hybrid simulation code,the total stopping power is the sum of the contributions of the free electron stopping power and the bound electron stopping power.For the resistivity model,we have fully considered the electron collision frequency for different temperature ranges,including the electron-phonon collision rate at low temperture,the electron-electron collision rate at moderate temperature and the Spitzer regime at high temperature.Fourthly,the effects of the stopping power model,the resistive fields,the initial ion divergence and the material resistivity on the propagation of proton beams in solid target are studied.Hybrid simulations show that the range difference from different stopping power models will affect the energy deposition to the target.Both of the resistive field and ion scattering effects are important for the ion beam transport in solid target,they compete with each other.When the target is not completely ionized,the self-generated resistive field effect dominates compared with the ion scattering effect.However,when the target is completely ionized,the ion scattering dominates.Moreover,we also studied the importance of the ohmic heating in proton beam energy deposition and it shows that the energy fraction deposited as ohmic heating can be as high as 20-30%.In addition,it is found that the initial ion divergence is a physical factor that can not be ignored,which may modify the proton energy deposition distribution.Finally,the stopping power effects on ion driven fast ignition are investigated.It is found that the ion ranges obtained by BPS model are 20%higher than that from classical stopping power model for ion fast ignition conditions.The higher range leads to the increasing of the ignition energies.It also shows that the higher range has not too much effect on the optimal kinetic energy for Maxwellian protons.However,the optimal mean kinetic energy for quasi-mononenergetic carton ions is reduced from 300 MeV to 250MeV with the higher range,which is beneficial for ion fast ignition.