Oxford Centre for High Energy Density Science (OxCHEDS)

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:

Electron temperature and electron density in a dc plasma jet at atmospheric pressure have been obtained using Thomson laser scattering. Measurements performed at various scattering angles have revealed effects that are not accounted for by the standard scattering theory. Differences between the predicted and experimental results suggest that higher order corrections to the theory may be required, and that corrections to the form of the spectral density function may play an important role. © 1999 The American Physical Society.

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.

Abstract:

Transient x-ray diffraction is used to record time-resolved information about the shock compression of materials. This technique has been applied on Nova shock experiments driven using a hohlraum x-ray drive. Data were recorded from the shock release at the free surface of a Si crystal, as well as from Si at an embedded ablator/Si interface. Modeling has been done to simulate the diffraction data incorporating the strained crystal rocking curves and Bragg diffraction efficiencies. Examples of the data and post-processed simulations are presented. © 1999 American Institute of Physics.