Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

We present the first direct experimental observation of the parametric two-ion decay instability of ion-acoustic waves driven by a high intensity (5 x 10(15) W cm(-2)) laser beam in a laser produced high-Z plasma. Using two separate Thomson scattering diagnostics simultaneously, we directly measure the scattering from thermal ion-acoustic fluctuations, the primary ion waves that are driven to large amplitudes by the high intensity beam, and the two-ion decay products. The decay products are shown to be present only where the interaction takes place and their k spectrum is broad.

Abstract:

The measurement of the saturation of stimulated Brillouin scattering (SBS) by an ion-trapping-induced frequency shift was investigated. It was achieved by directly measuring the amplitude and absolute frequency of SBS-driven ion-acoustic waves (IAW). A frequency of up to 30% was observed along with a saturation of driven SBS and IAW reflectivity. The fast 30 ps oscillations of the SBS-driven IAW amplitude induced by the frequency shift were also measured.

Abstract:

We report the first measurement of the saturation of stimulated Brillouin scattering (SBS) by an ion-trapping-induced frequency shift, which was achieved by directly measuring the amplitude and absolute frequency of SBS-driven ion-acoustic waves (IAW). A frequency shift of up to 30% and a simultaneous saturation of driven IAW and SBS reflectivity were observed. The scaling of the frequency shift with the IAW amplitude compares well with theoretical calculations. We have further measured fast 30 ps oscillations of the SBS-driven IAW amplitude induced by the frequency shift.

Abstract:

The VULCAN laser was used for investigating ⁷Li(p,n) ⁷Be reactions with the help of Cu and CH primary and LiF secondary targets. CR-39 plastic track detector measured the neutron yield which was 3×10 ¹⁹ Wcm ^-2 for CH primary targets and up to 2×10 ⁸ sr ^-1 for Cu primary targets. At various angles, the angular distribution of neutrons was measured that indicated a relatively anisotropic distribution of neutrons over 180°. The reactions were found to be fficient for neutron radiography on high repetition, table-top lasers.

Abstract:

The energy transport properties were investigated within a dense plasma using a Kα fluorescence layer. A spherically bent Bragg crystal monochromatic two-dimensional (2D) x-ray imaging technique was utilized to record the origin of Kα photons created in a 20 μm thick buried Ti or Cu fluor layer in a planar Al or CH target. It was found that one or more processes cause lower energy electrons to travel at very large angles very near the front surface of the target. The results show that laser generated electrons penetrating through more than 100 μm of Al, emerge from a >150 μm wide region and travel in a 40° full-width cone.