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Abstract:

The first experimental study of the propagation of electrons created by an intense laser in shock-compressed matter has been performed with the VULCAN laser facility at the Rutherford Appleton Laboratory, to investigate one of the fundamental phases of the fast ignitor concept for inertial confinement fusion. Plastic plane targets were irradiated on one side with two pulsed laser beams, each with I ≈ 1014 W/cm2, t ≈ 2 ns, E ≈ 80 J per pulse, to generate a planar shock wave; on the opposite side of the target, a chirped pulse amplification (CPA) laser beam (I ≈ 1016W/cm2, t ≈ 3 ps, E ≈ 10 J) was focused to generate the fast electrons. The results show an increase of hot electron penetration in compressed matter with respect to an ordinary one. Experimental results have been analyzed with computer simulations.

Abstract:

The Strickland-Mourou technique of Chirped Pulse Amplification (CPA) is now in common use on many laser systems and has resulted in massive increases in focused intensities. Implemented on the Vulcan laser system, the technique has generated multi-Joule subpicosecond pulses whilst maintaining beam quality to produce focused intensities of 5×1019 W cm-2.

Abstract:

The interaction of ultra-intense focused laser beams with solid targets is a new field of research resulting in the production of exotic plasma conditions similar to the conditions which exist in the interior of some stellar objects. The lasers generate very high energy electrons and ions which can subsequently produce γ-rays, positrons, neutrons and pions. The results obtained from these studies have major implications to fundamental plasma physics and high energy accelerator physics as well as important technological potential for the production of compact sources of neutrons, positrons and isotopes.

Abstract:

Novel measurements of electromagnetic radiation above 10 MeV are presented for ultra intense laser pulse interactions with solids. A bright, highly directional source of y rays was observed directly behind the target. The y rays were produced by bremsstrahlung radiation from energetic electrons generated during the interaction. They were measured using the photoneutron reaction [63Cu(γ,n)62Cu] in copper. The resulting activity was measured by coincidence counting the positron annihilation γ rays which were produced from the decay of 62Cu. New measurements of the bremsstrahlung radiation at 1019 W cm-2 are also presented. © 1999 American Institute of Physics.

Abstract:

We report on shadowgraphic measurements showing the first space- and time-resolved snapshots of ultraintense laser pulse-generated fast electrons propagating through a solid target. A remarkable result is the formation of highly collimated jets (<20-μm) traveling at the velocity of light and extending up to 1 mm. This feature clearly indicates a magnetically assisted regime of electron transport, of critical interest for the fast ignitor scheme. Along with these jets, we detect a slower (≈c/2) and broader (up to 1 mm) ionization front consistent with collisional hot electron energy transport. 1999 © The American Physical Society.