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We use one- and two-dimensional particle-in-cell simulations to demonstrate that the propagation of an ultraintense laser (I = 1019W/cm²) in critical density plasma can be interfered with by a high density plasma wall region generated at the propagation front. When the electron flow speed of the wall region exceeds a certain relativistic threshold, the region behaves as an overdense plasma due to a decrease of the effective critical density. The region forms then very small overdense plasma islands. The islands impede the propagation intermittently and slow down the propagation speed significantly. [ABSTRACT FROM AUTHOR]

Channeling experiments were performed that demonstrate the transport of high-intensity (>1018 W/cm²), multikilojoule laser light through a millimeter-sized, inhomogeneous (~300-/um density scale length) laserproduced plasma up to overcritical density, which is an important step forward for the fast-ignition concept. The background plasma density and the density depression inside the channel were characterized with a novel optical probe system. The channel progression velocity was measured, which agrees well with theoretical predictions based on large scale particle-in-cell simulations, confirming scaling laws for the required channeling laser energy and laser pulse duration, which are important parameters for future integrated fast-ignition channeling experiments. [ABSTRACT FROM AUTHOR]

Nonthermal acceleration of relativistic electrons is investigated with an intensive laser pulse. An energy distribution function of energetic particles in the universe or cosmic rays is well represented by a power-law spectrum, therefore, nonthermal acceleration is essential to understand the origin of cosmic rays. A possible candidate for the origin of cosmic rays is wakefield acceleration at relativistic astrophysical perpendicular shocks. The wakefield is considered to be excited by large-amplitude precursor light waves in the upstream of the shocks. Substituting an intensive laser pulse for the large amplitude light waves, we performed a model experiment of the shock environments in a laboratory plasma. An intensive laser pulse was propagated in a plasma tube created by imploding a hollow polystyrene cylinder, as the large amplitude light waves propagated in the upstream plasma at an astrophysical shock. Nonthermal electrons were generated, and the energy distribution functions of the electrons have a power-law component with an index of ∼2. We described the detailed procedures to obtain the nonthermal components from data obtained by an electron spectrometer. [ABSTRACT FROM AUTHOR]