Order-of-magnitude increase in laser-target coupling at near-relativistic intensities using compound parabolic concentrators.

Achieving a high conversion efficiency into relativistic electrons is central to short-pulse laser application and fundamentally relies on creating interaction regions with intensities ≫10^{18}W/cm^{2}. Small focal length optics are typically employed to achieve this goal; however, this solution is impractical for large kJ-class systems that are constrained by facility geometry, debris concerns, and component costs. We fielded target-mounted compound parabolic concentrators to overcome these limitations and achieved nearly an order-of-magnitude increase to the conversion efficiency and more than tripled electron temperature compared to flat targets. Particle-in-cell simulations demonstrate that plasma confinement within the cone and formation of turbulent laser fields that develop from cone wall reflections are responsible for the improved laser-to-target coupling. These passive target components can be used to improve the coupling efficiency for all high-intensity short-pulse laser applications, particularly at large facilities with long focal length optics.

Time-Resolved Fuel Density Profiles of the Stagnation Phase of Indirect-Drive Inertial Confinement Implosions.

The implosion efficiency in inertial confinement fusion depends on the degree of stagnated fuel compression, density uniformity, sphericity, and minimum residual kinetic energy achieved. Compton scattering-mediated 50-200 keV x-ray radiographs of indirect-drive cryogenic implosions at the National Ignition Facility capture the dynamic evolution of the fuel as it goes through peak compression, revealing low-mode 3D nonuniformities and thicker fuel with lower peak density than simulated. By differencing two radiographs taken at different times during the same implosion, we also measure the residual kinetic energy not transferred to the hot spot and quantify its impact on the implosion performance.

Production of relativistic electrons at subrelativistic laser intensities.

Relativistic electron temperatures were measured from kilojoule, subrelativistic laser-plasma interactions. Experiments show an order of magnitude higher temperatures than expected from a ponderomotive scaling, where temperatures of up to 2.2 MeV were generated using an intensity of 1×10^{18}W/cm^{2}. Two-dimensional particle-in-cell simulations suggest that electrons gain superponderomotive energies by stochastic acceleration as they sample a large area of rapidly changing laser phase. We demonstrate that such high temperatures are possible from subrelativistic intensities by using lasers with long pulse durations and large spatial scales.

[The prevalence of sicca symptoms in Iceland.].

OBJECTIVES: Sjoegren' syndrome is one of the most common inflammatory systemic rheumatic disorders. The syndrome is characterised by tiredness, pain problems and mucosal dryness. The goal of this study is to elucidate the prevalence of sicca symptoms in the Icelandic population and to calculate the preliminary prevalence value for Sjoegren' syndrome in Iceland. MATERIAL AND METHODS: Random sample was retrieved from two age groups; 40-49 and 70-75 years Icelandic inhabitants of Reykjavík and Akureyri. Questionnaire with 14 questions of the most common symptoms of Sjoegren' syndrome was mailed to those sampled. A small sample was evaluated by Schirmer-I test, tear film break up time (BUT) and Rose Bengal score for keratoconjunctivitis sicca (KCS) and unstimulated salivary flow rate was performed. RESULTS: The questionnaire was sent to 621 subjects, 300 male and 321 female. The response rate was 74%. Of those 20.3% had subjective symptoms of dry eyes and 12.0% of dry mouth according to the six questions used in the European classification criteria (EEC). The prevalence of both was higher in females (p<0.05). Of the 23 subjects who reported sicca symptoms, fatigue and pain problems; 26% had abnormal Shirmer-I test, 13% had abnormal BUT and 39% had abnormal salivary flow rate, two of those individuals fulfilled the EEC criteria for Sjoegren' syndrome (0.2%; 0-0.5%, 95% CI). None in the age and sex matched control group fulfilled the EEC criteria. CONCLUSION: The subjective symptoms of dry eye and dry mouth are common in Iceland, as are the three major symptoms of Sjoegren' syndrome. Standardised objective diagnostic criteria is necessary when the diagnosis of the syndrome is made.