| In recent years, laser pulses with focused intensities I ~ 1018~22 W /cm2 and pulse width r < Ips are available in many laboratories. The study of the interaction of ultra-short ultra-intense laser pulses with overdense plasmas, which is motivated primarily by the fast ignition scheme of inertial confinement fusion, has received more and more attention. This thesis is devoted to studying those issues relevant to the interaction of ultra-short ultra-intense laser pulses with overdense plasmas, including the generation and transport of relativistic electron beams, the generation of quasistatic magnetic field, the energetic ions production, and the influence of preplasma on electrons acceleration.We developed a 2D3V(two dimensional in space and three dimensional in velocity) particle-in-cell code APIC2D. In this code, we improved some algorithms of particle simulation as following:1. An advanced Borris rotation method is proposed to solve the relativistic Lorentz equation. The method can describe the relativistic dynamic behavior of particles accurately and is especially adaptive to simulate the dynamic behavior of particles in ultra-intense laser field.2. A charge conserving current weighting algorithm, which is based on the current conservation equation, is used in the code. However, the application of particle boundary condition may destroy the validity of the method. We present some methods to ensure the rigorous charge conservation.With our code APIC2D, the following physics problems are studied:1. The interaction of ultra-short ultra-intense laser pulses with overdense plasmas are simulated. Laser hole boring effect due to the large ponderomotive force is observed on the surface which is verticle to the magnetic field. As for the phenomena on the surface which is verticle to the electric field, the plasma surface oscillations are generated, and then electron bubbles and ion bubbles are formed. Quasistatic magnetic fields are generated by the laser driven relativistic electron stream.2. The transport of a relativistic-electron-beam(REB) in dense plasmas with a cold return electron current is examined by theory and particle simulation. Using the two-stream fluid model, the linear dispersion relation is derived assuming a two-dimensional spatial geometry. Two cases are considered, one is that the 2D spatial geometry is defined by the plane containing the two counterstreaming electron populations and the perturbation wave vector(referred as the XY plane), and the other is that the geometry is defined by the plane being vertical to the two counterstreaming electron populations(referred as the YZ plane). The transport of REB is examined by2D3V particle simulation in the XY plane. The filamentation and coalescence of currents and related magnetic field pattern, caused by the two-dimensional electromagnetic-beam-plasma(EMBP) instability, are observed. Because of the resonant interaction between the REB electrons and the wave excitated by the EMBP instability, the REB electrons cannot transport continuously, but in form of current clumps. The transport velocity is close to the phase velocity of the wave. The transport of REB is also investigated by 2D3V particle simulation in the YZ plane. A large number of Current filaments emerge in the system. Those filaments self-organize in coaxial structures where the relativistic current in the center is surrounded by intense magnetic field and the return current sheath, and the magnetic field decreases abruptly to zero outside the relativistic current.3. The generation of energetic ions during the interaction of a linear-polarized ultra-short ultra-intense laser pulse with solid targets are examined by particle simulation. Three energetic ion populations are observed and the acceleration mechanisms are analyzed, respectively. The first population is pulled out from the target by the electron jet in front of the target. The second population is pulled forwards by the propagating energetic electrons. The third energetic ion popu...
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