Characterizing optical depth effects in cylindrical plasmas for density diagnostics in ICF plasmas*

Temperature and density diagnostics are critical for understanding laser coupling to high-Z hohlraums in ICF experiments at the National Ignition Facility. Over the past few years, there has been an effort to develop accurate diagnostic methods using x-ray spectroscopy of dot targets placed inside the hohlraum. The cylindrical geometry of these dots causes the intensity of the optically thick lines to have a non-trivial angular dependence. The degree of anisotropy is a function of the aspect ratio (H/R) of the dots and can provide information about their geometry (including their density). The OpticalDepth campaign at OMEGA laser aims for a better characterization of this effect. To keep the system as simple as possible, we have developed a platform to create a uniform cylindrical plasma by using microdots of a mid-Z material in order to use K-shell x-ray spectroscopy. The OMEGA target chamber configuration allows us to obtain spectra and images of the plasma expansion in the axial and radial directions. The simulations present good agreement with data, showing the potential capabilities of this method as a density diagnostic.