Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

The angular distribution of bremsstrahlung gamma rays produced by fast electrons accelerated in relativistic laser-solid interaction has been studied by photoneutron activation in copper. We show that the gamma-ray beam moves from the target normal to the direction of the k(laser) vector as the scale length is increased. Similar behavior is found also in 2D particle-in-cell simulations.

Abstract:

When a laser pulse of intensity 1019 W cm−2 interacts with solid targets, electrons of energies of some tens of MeV are produced. In a tantalum target, the electrons generate an intense highly directional γ-ray beam that can be used to carry out photonuclear reactions. The isotopes 11C, 38K, 62,64Cu, 63Zn, 106Ag, 140Pr, and 180Ta have been produced by (γ, n) reactions using the VULCAN laser beam. In addition, laser-induced nuclear fission in 238U has been demonstrated, a process which was theoretically predicted at such laser intensities more than ten years ago. The ratio of the 11C and the 62Cu β+ activities yields shot-by-shot temperatures of the suprathermal electrons at laser intensities of ∼1019 W cm−2. © 2000 The American Physical Society.

Abstract:

Protons with energies up to 18 MeV have been measured from high density laser-plasma interactions at incident laser intensities of 5×1019W/cm2. Up to 1012 protons with energies greater than 2 MeV were observed to propagate through a 125µm thick aluminum target and measurements of their angular deflection were made. It is likely that the protons originate from the front surface of the target and are bent by large magnetic fields which exist in the target interior. To agree with our measurements these fields would be in excess of 30 MG and would be generated by the beam of fast electrons which is also observed. © 2000 The American Physical Society.

Abstract:

We present high-resolution spectroscopic measurements of the optically thick hydrogen-like Al Ly-α line shape from a cylindrically expanding plasma. The cylindrical expansion is produced by symmetrically irradiating a 120 μm diameter coated wire target with six beams of the VULCAN Nd:glass laser at an irradiance of 2×1014Wcm-2. Small shifts in the line position and changes in the line shape can be attributed to radiation emitted from different regions of the plasma and passing through different gradients in plasma density, temperature, and velocity. The experimental profiles are compared to a time-dependent hydrodynamics code incorporating a Sobolev escape probability treatment of the radiative transport. © 2000 Elsevier Science B.V.