Overlapped Stark profiles of coincident x-ray lines as possible diagnostics of core-shell mixing in spherical plasma implosions

One of the most serious obstacles to the attainment of high-gain inertial confinement fusion is the loss of implosion symmetry and mixing of core and shell material, principally as a result of Rayleigh-Taylor instabilities. As a diagnostic of such instabilities, we have investigated the consequences of such mixing on the emergent composite Stark profile of the heliumlike potassium 1${\mathit{s}}^2$–1s2p ${}_{}{}^1{}_{}{}^{}$ ${\mathit{P}}_1$ and hydrogenic chlorine 1s-3p lines that are coincident at 3.53 Å (3.51 keV). For the case of a chlorine-filled core compressed by a potassium-bearing shell, detailed radiative transfer calculations with self-consistently calculated Stark profiles reveal changes in the overlapped emission profile of these lines when the potassium is assumed mixed into the core. When the potassium remains localized in a distinct shell, its major effect on the chlorine profile is to produce an absorption feature. When the two elements mix to various degrees, the depth of this feature is reduced. This is explained by pumping of the K x v i i i 1s2p ${}_{}{}^1{}_{}{}^{}$ ${\mathit{P}}_1$ state by the Cl ${\mathrm{L}}_{\mathrm{\beta }}$ line, and obscuration of the potassium emission by the chlorine opacity. Experimental detection of this effect would require spectral resolution of about 2 eV and the ability to discriminate intensity differences of 15% in nearby spectral regions.