Professor Steven Rose

Abstract:

We present measurements of the H-like potassium (K xix) X-ray spectrum and its He-like (K xviii) satellite lines, which are situated in the wavelength region between 3.34 and 3.39 Å, which has been of interest for the detection of dark matter. The measurements were taken with a high-resolution X-ray spectrometer from targets irradiated by a long-pulse (2 ns) beam from the Orion laser facility. We obtain experimental wavelength values of dielectronic recombination satellite lines and show that the ratio of the Lyα lines and their dielectronic satellite lines can be used to estimate the electron temperature, which in our case was about 1.5 ± 0.3 keV.

Abstract:

Understanding the effects of radiative transfer in High Energy Density Physics experiments is critical for the characterization of the thermodynamic properties of highly ionized matter, in particular in Inertial Confinement Fusion (ICF). We report on non-Local Thermodynamic Equilibrium experiments on cylindrical targets carried out at the Omega Laser Facility at the Laboratory for Laser Energetics, Rochester NY, which aim to characterize these effects. In these experiments, a 50/50 mixture of iron and vanadium, with a thickness of 2000 Å and a diameter of 250 μm, is contained within a beryllium tamper, with a thickness of 10 μm and a diameter of 1000 μm. Each side of the beryllium tamper is then irradiated using 18 of the 60 Omega beams with an intensity of roughly 3 × 1014 W cm−2 per side, over a duration of 3 ns. Spectroscopic measurements show that a plasma temperature on the order of 2 keV was produced. Imaging data show that the plasma remains cylindrical, with geometrical aspect ratios (quotient between the height and the radius of the cylinder) from 0.4 to 2.0. The temperatures in this experiment were kept sufficiently low (∼1–2 keV) so that the optically thin Li-like satellite emission could be used for temperature diagnosis. This allowed for the characterization of optical-depth-dependent geometric effects in the vanadium line emission. Simulations present good agreement with the data, which allows this study to benchmark these effects in order to take them into account to deduce temperature and density in future ICF experiments, such as those performed at the National Ignition Facility.