Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

We have performed measurements of the radiation and the hot electron temperature in sub-millimetre size hohlraums driven by a high intensity short-pulse laser. The results indicate that radiation temperatures ∼80 eV can be obtained with ∼20 J of laser energy delivered on target. Radiation-hydrodynamics simulations indicate an absorption into thermal X-rays of ≲1-2%, with peak temperatures similar to those measured experimentally. Crown Copyright © 2009.

Abstract:

Numerical studies are conducted on the electron injection into the first acceleration bucket of a laser wakefield by a weak counter-propagating laser pulse. It is shown that there are two injection mechanisms involved during the colliding laser interaction, the collective injection and stochastic injection. They are caused by the time-averaged ponderomotive force push and stochastic acceleration in the interfering fields, respectively. The threshold amplitude of the injection laser pulse is estimated for the occurrence of electron injection, which is close to that for stochastic acceleration and depends weakly upon the plasma density. The trapping of a large number of injection electrons can result in significant decay of the laser wakefield behind the first wave bucket. © EDP Sciences and Springer 2009.

Abstract:

X-ray harmonic radiation extending to 3.3 Å, 3.8 keV from Petawatt class laser-solid interactions is presented. The harmonic spectra display a relativistic limit scaling up to ∼3000th order, above which an intensity dependent scaling roll-over is observed. Highly directional beamed emission for harmonic photon energy hv > 1 keV is found to be into a cone angle < 4°, significantly less than that of the incident laser cone (20°). © EDP Sciences and Springer 2009.