Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Electron beam hollowing in a plasma is investigated using an analytical, rigid beam model and two different hybrid codes in an attempt to explain observations of hollow plasma formations on the back of plastic targets in experiments carried out on the Vulcan terawatt laser. The relevance of the results to electron transport in fast ignition inertial confinement fusion is considered using dimensionless scaling parameters. © 2006 IOP Publishing Ltd.

Abstract:

A flexible multi-channel neutron spectrometer has been constructed to measure both the ion temperature and acceleration mechanisms in ultra-intense laser-plasma interactions. Angularly resolved neutron spectra are required to deduce the momentum distribution of ions accelerated by the intense electric field. The first neutron spectra have been obtained using this instrument in a 100-TW class laser interaction with deuterated plastic targets. These show a slight Doppler shift to lower energy side of the center of mass energy of d (d, n)3 He reactions at 2.45 MeV. A three-dimensional Monte-Carlo calculation of the neutron generation confirms the fast ion acceleration from the rear side of a solid target which has a Maxwellian momentum distribution. © 2006 Elsevier B.V. All rights reserved.

Abstract:

We propose a modified x-ray form factor that describes the scattering cross section in warm dense matter valid for both the plasma and the solid (crystalline) state. Our model accounts for the effect of lattice correlations on the electron-electron dynamic structure, as well as provides a smooth transition between the solid and the plasma scattering cross sections. In addition, we generalize the expression of the dynamic structure in the case of a two-temperature system (with different electron and ion temperatures). This work provides a unified description of the x-ray scattering processes in warm and dense matter, as the one encountered in inertial confinement fusion, laboratory astrophysics, material science, and high-energy density physics and it can be used to verify temperature relaxation mechanisms in such environments.

Abstract:

Protons accelerated by a picosecond laser pulse have been used to radiograph a 500μm diameter capsule, imploded with 300 J of laser light in 6 symmetrically incident beams of wavelength 1.054μm and pulse length 1 ns. Point projection proton backlighting was used to characterize the density gradients at discrete times through the implosion. Asymmetries were diagnosed both during the early and stagnation stages of the implosion. Comparison with analytic scattering theory and simple Monte Carlo simulations were consistent with a 3±1g/cm3 core with diameter 85±10μm. Scaling simulations show that protons >50MeV are required to diagnose asymmetry in ignition scale conditions. © 2006 The American Physical Society.