Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Nail-wire targets (20 μm diameter copper wires with 80 μm hemispherical head) were used to investigate energy transport by relativistic fast electrons generated in intense laser-plasma interactions. The targets were irradiated using the 300 J, 1 ps, and 2 × 1020 W · cm-2 Vulcan laser at the Rutherford Appleton Laboratory. A spherically bent crystal imager, a highly ordered pyrolytic graphite spectrometer, and single photon counting charge-coupled device gave absolute Cu Kα measurements. Results show a concentration of energy deposition in the head and an approximately exponential fall-off along the wire with about 60 μm 1/e decay length due to resistive inhibition. The coupling efficiency to the wire was 3.3 ± 1.7% with an average hot electron temperature of 620 ± 125 keV. Extreme ultraviolet images (68 and 256 eV) indicate additional heating of a thin surface layer of the wire. Modeling using the hybrid E-PLAS code has been compared with the experimental data, showing evidence of resistive heating, magnetic trapping, and surface transport. © 2009 American Institute of Physics.

Abstract:

We present the first ultrafast temporally, spectrally, and angularly resolved x-ray scattering measurements from shock-compressed matter. The experimental spectra yield the absolute elastic and inelastic scattering intensities from the measured density of free electrons. Laser-compressed lithium-hydride samples are well characterized by inelastic Compton and plasmon scattering of a K-alpha x-ray probe providing independent measurements of temperature and density. The data show excellent agreement with the total intensity and structure when using the two-species form factor and accounting for the screening of ion-ion interactions.

Abstract:

We present the first ultrafast temporally, spectrally, and angularly resolved x-ray scattering measurements from shock-compressed matter. The experimental spectra yield the absolute elastic and inelastic scattering intensities from the measured density of free electrons. Laser-compressed lithium-hydride samples are well characterized by inelastic Compton and plasmon scattering of a K-α x-ray probe providing independent measurements of temperature and density. The data show excellent agreement with the total intensity and structure when using the two-species form factor and accounting for the screening of ion-ion interactions. © 2009 The American Physical Society.

Abstract:

The temporal resolution of existing streak cameras are limited by electron transit time dispersion. Here we present a state-of-art design compensating this to achieve a breakthrough of 100fs time resolution. © 2009 Optical Society of America.

Abstract:

The production of highly energetic beams of both electrons and ions is a major part of the experimental programme at the Central Laser Facility (CLF), STFC Rutherford Appleton Laboratory. Every year sees a significant number of experiments done in both areas. This has been complemented by theoretical studies that have been carried out at the CLF and UK universities. In a recent consultation on plans to build a 10 PW upgrade to the VULCAN facility, laser-driven particle acceleration formed a very significant part of the science case that emerged from this consultation. In this talk, I will review the experimental progress that has been made in particle acceleration, and I will also examine what theoretical investigations suggest the future of this field will be. Experimental studies of laser-driven ion acceleration of the CLF using both the VULCAN and ASTRA systems have looked at a number of aspects including focussing and control of the ion beam, manipulation of the energy spectrum, energy scaling with laser and target parameters, and direct use of the proton beam in both isochoric heating of secondary targets and proton radiography. Recently there has been great interest in a number of theoretical studies which indicate that it should be possible to explore radiation-pressure driven ion acceleration for intensities above 1021 Wcm-2, which will be accessible with the ASTRA-GEMINI system. This very exciting prospect will also be discussed. Electron acceleration in laser wakefields is also a well established part of the CLF programme. Experimental studies of laser-driven electron acceleration using the ASTRA laser have explored electron acceleration in both supersonic gas jets and gas-filled capillaries. This has led to the production of electron bunches with up to 1 GeV energy and a few percent energy spread. The influence of tuneable parameters such as the evolution of the plasma channel inside a capillary or the position of the laser focus with respect to the gas jet is actively being investigated. These efforts are backed up by a matching numerical campaign. Recent experiments have also shown that electron bunches trapped on a downward density ramp can have a very small absolute energy spread, and the potential consequences of these results will also be discussed. © 2011 Optical Society of America.