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The first report on a model experiment of cosmic ray acceleration by using intense laser pulses is presented. Large amplitude light waves are considered to be excited in the upstream regions of relativistic astrophysical shocks and the wakefield acceleration of cosmic rays can take place. By substituting an intense laser pulse for the large amplitude light waves, such shock environments were modeled in a laboratory plasma. A plasma tube, which is created by imploding a hollow polystyrene cylinder, was irradiated by an intense laser pulse. Nonthermal electrons were generated by the wakefield acceleration and the energy distribution functions of the electrons have a power-law component with an index of ∼2. The maximum attainable energy of the electrons in the experiment is discussed by a simple analytic model. In the incoherent wakefield the maximum energy can be much larger than one in the coherent field due to the momentum space diffusion or the energy diffusion of electrons. [ABSTRACT FROM AUTHOR]

By using a cone attached to a capillary, electrons generated through a laser interaction were autoinjected and accelerated in a low-density wake field. The cone attached to the entrance of the capillary serves as an electron supplier. It increases the number of electrons from below the detection limit to 1.1 pC and the energy from 4 to 30 MeV. A two-dimensional particle-in-cell simulation reveals that a significant number of energetic electrons are extracted from the surface of the cone and are subsequently trapped in the wake field and accelerated in the capillary. [ABSTRACT FROM AUTHOR]

We have developed an advanced design for a time-of-flight (TOF) neutron spectrometer applied to the study of ultraintense laser-plasma interactions in the area of fast ignition research. The interaction of an ultraintense laser pulse with plasma creates intense gamma rays, which generate a high level of background noise in the thermal neutron detection process. High energy-density ions, which are generated by strong electric fields associated with the laser interactions, produce beamlike fusion neutrons with an angular distribution that is dependent on the momentum distribution of the ions. These beamlike fusion neutrons also act as a source of significant background noise in the thermal neutron detection process. In order to improve the signal-to-noise ratio (S/N), we have proposed and applied a wave-coincidence method to the neutron detection process. We have demonstrated the advantages of this advanced method in ultraintense laser-plasma interaction experiments, where an improvement in S/N by a factor of 7–8 compared to the conventional TOF method was achieved. We have calculated that the value of S/N increases with the number of detectors used as well as with the initial value of S/N for a single detector. [ABSTRACT FROM AUTHOR]

Energetic electrons were generated by the interaction of a high-intensity laser pulse with a plasma preformed from a hollow plastic cylinder via laser-driven implosion. The spectra of a comparatively high-density plasma ∼1019 cm-3 had a bump around 10 MeV. Simple numerical calculations explained the spectra obtained in this experiment. This indicates that the plasma tube has sufficient potential to convert a Maxwellian spectrum to a comparatively narrow spectrum. [ABSTRACT FROM AUTHOR]