Prof Peter Norreys FInstP;

Abstract:

With the addition of recent PW shots, the propagation of short-pulse laser generated electron beams have been studied using laser pulse energies from 30 J to 300 J, generating currents up to ∼15 MA in solid Al:Cu targets. This is ∼5% of the current that will be required in an ignition pulse. To this level, the current appears to simply scale with laser power, the propagation spread not change at all. The resistance of the aluminum does not seem to play a role in the propagation characteristics, though it might in setting the current starting parameters. We do find that at the highest currents parts of these targets reach temperatures high enough to modify the Cu-K2 emission spectrum rendering our Bragg imaging mirrors ineffective; spectrometers will be needed to collect data at these higher temperatures. © EDP Sciences.

Abstract:

Petawatt capability on the Vulcan laser facility has been available to the international plasma physics community for over two years. This has enabled novel experiments to be carried out and new regimes of physics to be explored. During that time, there have been 10 successful user experiments with 89% of shots delivered within the requested energy limits. In the autumn of 2004, pulses with powers of more than a petawatt (1015Watts) were delivered to target with energies greater than 400 J and pulse widths shorter than 500 femtoseconds (10-15) on target. In parallel to the development of ultra-high intensity pulses is a programme to enhance Vulcan's long pulse capabilities. This paper will present an overview of the current capabilities of the Vulcan Petawatt facility and discuss some of the recent technological advances that have enabled the generation of Petawatt pulses. © EDP Sciences.

Abstract:

Isochoric heating by electrons has been measured in the two limiting cases of small area thin foils with dominant refluxing and cone-long-wire geometry with negligible refluxing in the wire. Imaging of Cu K alpha fluorescence, crystal x-ray spectroscopy of Cu K shell emission, and XUV imaging at 68eV and 256eV are discussed. Laser power on target was typically 0.5 PW in 0.7ps. Heating by focused proton beams generated at the concave inside surface of a hemi-shell and from a sub hemi-shell inside a 30 degrees cone has been studied with the same diagnostic methods plus imaging of proton induced K alpha. Conversion efficiency to protons has been measured and modeled. Conclusions from the experiments, links to theoretical understanding and relevance to fast ignition are outlined.

Abstract:

A hot, 2 to 3 keV electron temperature surface plasma was observed in the interaction of a 0.7 ps petawatt laser beam with solid copper-foil targets at intensities > 1020 W cm2. Copper K-shell spectra were measured in the range of 8 to 9 keV using a single-photon-counting x-ray charged-coupled-device camera. In addition to Kα and KΒ inner-shell lines, the emission contained the Cu Heα and Lyα lines, allowing the temperature to be inferred. These lines have not been observed previously with ultrafast laser pulses. For intensities less than 3× 1018 W cm2, only the Kα and KΒ inner-shell emissions are detected. Measurements of the absolute Kα yield as a function of the laser intensity are in general agreement with a model that includes refluxing and confinement of the suprathermal electrons in the target volume. © 2006 American Institute of Physics.