The use of geometric effects in diagnosing ion density in ICF-related dot spectroscopy experiments

Abstract We describe a method to calculate the ion density of High Energy Density (HED) cylindrical plasmas used in Dot Spectroscopy experiments. This method requires only spectroscopic measurements of the He α region obtained from two views (Face-on and Side-on). We make use of the fact that the geometry of the plasma affects the observed flux of optically thick lines. The ion density can be derived from the aspect ratio (height-to-radius) of the cylinder and the optical depth of the He α - y line (1 s 2 p 3 P 1  → 1 s 2 1 S 0 ). The aspect ratio and the optical depth of the y line are obtained from the spectra using ratios measured from the two directions of emission of the optically thick He α - w line (1 s 2 p 1 P 1  → 1 s 2 1 S 0 ) and the ratio of the optically thick to thin lines. The method can be applied to mid-Z elements at ion densities of 10 19 − − 10 20 cm − 3 and temperatures of a the order of keV, which is a relevant regime for Inertial Confinement Fusion (ICF) experiments.