Picosecond Time-resolved Observations of Dense Plasma Shifts

Picosecond time-resolved X-ray spectroscopy is used to measure the spectral line shift of the 1s2p-1s² transition in He-like Al ions as a function of the instantaneous plasma conditions. The plasma temperature and density are inferred from the Al He_α complex using a nonlocal-thermodynamic-equilibrium atomic physics model. The experimental spectra show a linearly increasing red shift for electron densities of 1 to 5 x 10²³ cm^-3. The measured line shifts are broadly consistent with a generalized analytic line-shift model based on calculations of a self-consistent field ion sphere model.