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The double laser pulse approach to relativistic electron beam (REB) collimation in solid targets has been investigated at the LULI-ELFIE facility. In this scheme two collinear laser pulses are focused onto a solid target with a given intensity ratio and time delay to generate REBs. The magnetic field generated by the first laser-driven REB is used to guide the REB generated by a second delayed laser pulse. We show how electron beam collimation can be controlled by properly adjusting the ratio of focus size and the delay time between the two pulses. We found that the maximum of electron beam collimation is clearly dependent on the laser focal spot size ratio and related to the magnetic field dynamics. Cu-Kα and CTR imaging diagnostics were implemented to evaluate the collimation effects on the respectively low energy (≤100 keV) and high energy (≥MeV) components of the REB. [ABSTRACT FROM AUTHOR]

Collimated transport of ultrahigh intensity electron current was observed in cold and in laser-shocked vitreous carbon, in agreement with simulation predictions. The fast electron beams were created by coupling high-intensity and high-contrast laser pulses onto copper-coated cones drilled into the carbon samples. The guiding mechanism--observed only for times before the shock breakout at the inner cone tip--is due to self-generated resistive magnetic fields of ~0.5-1 kT arising from the intense currents of fast electrons in vitreous carbon, by virtue of its specific high resistivity over the range of explored background temperatures. The spatial distribution of the electron beams, injected through the samples at different stages of compression, was characterized by side-on imaging of hard x-ray fluorescence. [ABSTRACT FROM AUTHOR]

The effect of target material on fast-electron transport is investigated using a high-intensity (0.7 ps, 1020 W/cm2) laser pulse irradiated on multilayered solid Al targets with embedded transport (Au, Mo, Al) and tracer (Cu) layers, backed with millimeter-thick carbon foils to minimize refluxing. We consistently observed a more collimated electron beam (36% average reduction in fast-electron induced Cu Kα spot size) using a high- or mid-Z (Au or Mo) layer compared to Al. All targets showed a similar electron flux level in the central spot of the beam. Two-dimensional collisional particle-in-cell simulations showed formation of strong self-generated resistive magnetic fields in targets with a high-Z transport layer that suppressed the fast-electron beam divergence; the consequent magnetic channels guided the fast electrons to a smaller spot, in good agreement with experiments. These findings indicate that fast-electron transport can be controlled by self-generated resistive magnetic fields and may have important implications to fast ignition. [ABSTRACT FROM AUTHOR]