Constraining magnitudes of nonzero temperature and density gradients using absorption spectra of radiatively heated target-foil plasma

We report the deduction of best-fit gradient-aligned profiles of temperature T and density n across tamped NaFMgO target-foil plasmas, heated and backlit by z-pinch radiation. Reliant on the minimization of a chi-squared statistic, our approach compares the spectroscopic output of a collisional-radiative model (PrismSPECT) with soft-xray absorption spectra collected on Sandia's Z Machine. Pattern of minimum-chi-squared in highly-dimensional parameter space is obtained with Monte Carlo sampling, and is seen to agree with a more efficient, two-parameter model. Results show that a nonzero gradient is likely to exist in both n and T, by virtue of the pinch-facing side of the foil absorbing the bulk of the incident energy. Predicted sensitivity of line spectra to the gradient-aligned profile of △T or △n is documented for each spectral feature, so that Stark broadening experienced by individual lines (for density) or line-area ratio between pairs of features (for temperature) may be assessed as proxies for the existence and quantification of such gradients.