Prof Peter Norreys FInstP;

Abstract:

Two critical issues related to the success of fast ignition inertial fusion have been vigorously investigated in a co-ordinated campaign in the European Union and the United States. These are the divergence of the fast electron beam generated in intense, PW laser-plasma interactions and the fast electron energy transport with the use of high intensity contrast ratio laser pulses. Proof is presented that resistivity gradient-induced magnetic fields can guide fast electrons over significant distances in (initially) cold metallic targets. Comparison of experiments undertaken in both France and the United States suggests that an important factor in obtaining efficient coupling into dense plasma is the irradiation with high intensity contrast ratio laser pulses, rather than the colour of the laser pulse itself. © 2010 IOP Publishing Ltd.

Abstract:

The experimental study of the behavior of deuterium plasma with densities between 2× 1018 and 2× 1020 cm-3, subjected to a 6 TW, 30 ps, 3× 1018 W cm-2 laser pulse, is presented. Conclusive experimental proof that a single straight channel is generated when the laser pulse interacts with the lowest densities is provided. This channel shows no small-scale longitudinal density modulations, extends up to 2 mm in length and persists for up to 150 ps after the peak of the interaction. Bifurcation of the channel after 1 mm propagation distance is observed for the first time. For higher density interactions, above the relativistic self-focusing threshold, bubblelike structures are observed to form at late times. These observations have implications for both laser wakefield accelerators and fast ignition inertial fusion studies. © 2010 American Institute of Physics.

Abstract:

The expansion of electromagnetic postsolitons emerging from the interaction of a 30? ps, 3×1018Wcm⊃-2 laser pulse with an underdense deuterium plasma has been observed up to 100? ps after the pulse propagation, when large numbers of postsolitons were seen to remain in the plasma. The temporal evolution of the postsolitons has been accurately characterized with a high spatial and temporal resolution. The observed expansion is compared to analytical models and three-dimensional particle-in-cell results, revealing a polarization dependence of the postsoliton dynamics. © 2010 The American Physical Society.

Abstract:

We present the progress made in developing IOPW OPCPA facility for the Vulcan laser to produce pulses with focused intensities >1023 Wcm-2. This power level will be delivered by generating pulses with >300J in 30fs. These pulses will be delivered to two target areas: in one target area they will be combined with the existing Vulcan Petawatt beamline and a new target area will be created for high intensity interactions. © 2010 Optical Society of America.

Abstract:

We demonstrate experimentally that the relativistic electron flow in a dense plasma can be efficiently confined and guided in targets exhibiting a high-resistivity-core-low-resistivity-cladding structure analogous to optical waveguides. The relativistic electron beam is shown to be confined to an area of the order of the core diameter (50μm), which has the potential to substantially enhance the coupling efficiency of electrons to the compressed fusion fuel in the Fast Ignitor fusion in full-scale fusion experiments. © 2010 The American Physical Society.