Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

Ion-acceleration processes were studied in ultraintense laser plasma interactions for normal incidence irradiation of solid targets. Neutron spectroscopy was used for the purpose of analysis. It was found that the ions are preferentially accelerated radially. Results show that the laser pedestal generates a 10 μm scale length in the coronal plasma with a 3 μm scale-length plasma near the critical density.

Abstract:

The use of a single-photon-counting x-ray charge-coupled device (CCD) camera as an x-ray spectrometer is a well-established technique in ultrashort-pulse laser experiments. In single-photon-counting mode, the pixel value of each readout pixel is proportional to the energy deposited from the incident x-ray photon. For photons below 100 keV, a significant fraction of the events deposits all the energy in a single pixel. A histogram of the pixel readout values gives a good approximation of the x-ray spectrum. This technique requires almost no alignment, but it is very sensitive to signal-to-background issues, especially in a high-energy petawatt environment. Shielding the direct line of sight to the target was not sufficient to obtain a high-quality spectrum, for the experiments reported here the CCD camera had to be shielded from all sides with up to 10 cm of lead. © 2004 American Institute of Physics.

Abstract:

The full aperture backscatter system provides a measure of the spectral power, and integrated energy scattered by stimulated Brillouin (348-354 nm) and Raman (400-800 nm) scattering into the final focusing lens of the first four beams of the NIF laser. The system was designed to provide measurements at the highest expected fluences with: (1) spectral and temporal resolution, (2) beam aperture averaging, and (3) near-field imaging. This is accomplished with a strongly attenuating diffusive fiber coupler and streaked spectrometer and separate calibrated time integrated spectrometers, and imaging cameras. A new technique determines the wavelength dependent sensitivity of the complete system with a calibrated Xe lamp. Data from the calibration system are combined with scattering data from targets to produce the calibrated power and energy measurements that show significant corrections due to the broad band calibrations. (C) 2004 American Institute of Physics.

Abstract:

A high-energy, ultraviolet Thomson scattering probe beam has been implemented on the Omega laser facility at the University of Rochester. The new probe operates at a wavelength of 264 nm, with a maximum energy of 260 J in a pulse length of 1 ns. The probe is focused with an F/6.7 lens to a minimum focal spot of 40 mum within a pointing tolerance of <50 mum. Data obtained from this probe beam have provided new diagnostic information on plasmas relevant for inertial confinement fusion and atomic physics studies. (C) 2004 American Institute of Physics.