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We have performed experiments using Callisto, the Vulcan 100 TW and the Vulcan Petawatt high intensity lasers to understand the characteristics of high energy, Kα x-ray sources and to implement workable radiography solutions at 20-100 keV. Our measurements show that the Kα size from a simple foil target is larger than 60 µm, far larger than the experiment resolution requirement. The total Kα yield is independent of target thicknesses verifying that refluxing plays a major role in photon generation. Smaller radiating volumes emit brighter Kα radiation. 1-D radiography experiments using small-edge-on foils resolved 10 µm features with high contrast.We tested a variety of small volume 2-D point sources such as cones, wires, and embedded wires, measuring photon yields and comparing our measurements with predictions from hybrid-PIC LSP simulations. In addition to high-energy, high-resolution backlighters, future experiments will also need imaging detectors and diagnostic tools that are workable in the 20-100 keV energy range. An initial look at some of these detector issues is also presented.

Measurement of magnetic fields generated by a high-energy, high-intensity laser-driven millimeter-scale Helmholtz coil target is reported. The magnetic field is derived from a reverse current that passes through two coils of 1.25-mm radius. A peak field of 7T with a time decay of 17ns is inferred from a series of induction coil measurements when the hot-electron temperature driving the reverse current is approximately ∼15keV. A simple model of the laser-driven Helmholtz coil target suggests how the target should be optimized to produce high-peak fields and indicates that peak magnetic fields above 100T are accessible. This could lead to exciting experiments in laser-plasma physics, in particular, experiments related to laboratory astrophysics.

The fast ignitor scheme for inertial confinement fusion requires forward driving of the critical density surface by light pressure (hole boring) to allow energy deposition close to the dense fuel. The recession velocity of the critical density surface has been observed to be v/c=0.015 at an irradiance of 1.0×1019 W cm−2 at a wavelength of 1.05 micron, in quantitative agreement with modeling.

Results from an experimental study of the collisionless interaction of two laser-produced plasmas in a magnetic field with applications to supernova remnant shock physics are presented. The dynamics of the two plasmas and their interaction are studied with and without magnetic field through spatially and temporally resolved measurements of the electron density. Experimental results show that counter-propagating collisionless plasmas interpenetrate when no magnetic field is present. In contrast, results obtained with the addition of a 7.5 T magnetic field perpendicular to plasma flow show density features in the interaction area that only occur when the field is present. The reason for this remains uncertain. It is suggested that this results from an increase in the effective collisionality as the magnetic field reduces the ion and electron gyroradius below the size of the experiment.

IntroductionSince the construction of the first Petawatt laser on the Nova laser facility at Lawrence Livermore National Laboratory we are witnessing the emergence of similar Petawatt-class laser systems at laboratories all around the world [i]. This new generation of lasers, able to deliver several hundred joules of energy in a sub-picosecond pulse, has enabled a host of new discoveries to be made and continues to provide a valuable tool to explore new regimes in relativistic laser-plasma physics-encompassing high energy X-rays and -rays, relativistic electrons, intense ion beams, and superstrong magnetic fields [ii,iii,iv]. The coupling in the near-future of multi-kiloJoule Petawatt-class lasers with large-scale fusion lasers-including the NIF and Omega EP (US), LIL (France), and FIREX (Japan)-will further expand opportunities in fast ignition, high energy X-ray radiography, and high energy density physics research.

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A high resolution technique for remotely sensing aerosol sulfate composition has been developed, based on the ratio of aerosol backscatter measured at 9.1 and 10.6 µm wavelengths with two continuous wave CO2 lidars. This is demontrated using data from the NASA GLObal Backscatter Experiment (GLOBE) over the Pacific Ocean in 1990. Results indicate changes from sulfuric acid with some ammoniation in clean conditions and presence of dust with ammoniated sulfates in continental plumes. Lidars provide good estimates of backscatter ratio with ∼5 second sample times (∼1 km spatial resolution) in aerosol concentrations as low as ∼10−2 µg/m³.