Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Our team has provided the first observations of energetic ion beam production from the front and rear surfaces thin foil targets upon irradiation by an intense laser beam in the relativistic regime. We invented a new plasma diagnostic technique in which "layered" track detectors and dosimetry media were used to simultaneously record ion angular emission patterns as well as ion spectral information. These results have led to a large number of further experiments in which similar measurement techniques were used and in which protons have been measured up to 58 MeV. The source and acceleration mechanisms for these proton beams have been extensively investigated. There have also been a number of proposed applications for these ion beams, such as for injectors into subsequent conventional acceleration stages, for probing of dense plasmas and for inertial confinement fusion experiments. © 2005 IEEE.

Abstract:

We review a recent experimental campaign to study the interaction physics of petawatt laser pulses incident at relativistic intensities on solid targets. The campaign was performed on the 500 J sub-picosecond petawatt laser at the Rutherford Appleton Laboratory. An extensive suite of optical, x-ray, and particle diagnostics was employed to characterise the processes of laser absorption, electron generation and transport, thermal and K-alpha x-ray generation, and proton acceleration.

Abstract:

Neutron time of flight signals have been observed with a high resolution neutron spectrometer using the petawatt arm of the Vulcan laser facility at Rutherford Appleton Laboratory from plastic sandwich targets containing a deuterated layer. The neutron spectra have two elements: a high-energy component generated by beam-fusion reactions and a thermal component around 2.45 MeV. The ion temperatures calculated from the neutron signal width clearly demonstrate a dependence on the front layer thickness and are significantly higher than electron temperatures measured under similar conditions. The ion heating process is intensity dependent and is not observed with laser intensities on target below 1020 W cm-2. The measurements are consistent with an ion instability driven by electron perturbations. © 2005 IOP Publishing Ltd.