Oxford Centre for High Energy Density Science (OxCHEDS)

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 charge state distributions of Fe, Na, and F are determined in a photoionized laboratory plasma using high resolution x-ray spectroscopy. Independent measurements of the density and radiation flux indicate unprecedented values for the ionization parameter xi=20-25 erg cm s(-1) under near steady-state conditions. Line opacities are well fitted by a curve-of-growth analysis which includes the effects of velocity gradients in a one-dimensional expanding plasma. First comparisons of the measured charge state distributions with x-ray photoionization models show reasonable agreement.

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.

Abstract:

The ultrafast heating of implosions using cone/shell geometeries was discussed. The study was carried out by using the 1054 nm, nanosecond, 0.9 kJ output of the VULCAN Nd:glass laser to drive 186 μm diameter, 6 μm wall thickness Cu-dopped deuterated plastic (CD) shells in 6-beam cubic symmetry. It was found that x-ray preheat, combined with lower ablation pressures, indicate that infrared drive was unlikely to be useful in full scale direct drive ignition design. The results show that the higher density of the compressed plasma promotes more collimated flow, but at the cost of reduced background heating.