Spatially-resolved spectra from a new uniform dispersion crystal spectrometer for characterization of Z-pinch plasmas

Abstract Based on self-focusing and uniform dispersion principle, a novel mica uniform dispersion crystal spectrograph (UDCS) was developed, whose linear dispersion was designed to be constant. An aluminum wire-array imploding experiment was performed at “Yang” accelerator and K-shell emission spectra were measured to investigate Z-pinch aluminum plasma characteristics by using the UDCS. The linear dispersion deduced from obtained spectra with linear fitting was in good agreement with the theoretical value. By using the collisional–radiative equilibrium (CRE) model, the intensity ratios of Ly-α/He-α line and Ly-β/He-e were given as a function of electron temperature. The measured intensity ratios were compared to the computed ones and the electron temperatures were estimated to be 512 eV and 489 eV. The slope of the free-bound X-ray continuum provides a model-independent diagnostic of the core electron temperature which was around 1215 eV for this implosion. Analysis of Z-pinch radial temperature gradient shows that the temperature decreases sharply near the core and slowly to the shell regions. Benefiting from the UDCS providing high spectral resolution ( λ /Δ λ ∼2500), the existence of first-order Langmuir dips were observed and reliably identified in Al Ly-α and Ly-γ resonance line profiles. The relationship between the position from the line center of red Langmuir dips and electron density was studied. The electron densities deduced from these fine spectral features were 5.52×10 21  cm −3 and 4.57×10 21  cm −3 respectively, which compared well with those derived from measurements of the line shift. The ion temperature was determined from the Doppler broadening of Al He-α resonance, He-like intercombination and Li-like s, t ( n =2) satellite lines.