Usefulness of x-ray diagnostics in dense-plasma gradients

The effect of electron temperature and ion density gradients on x-ray diagnostics for dense plasmas is studied. Time-independent calculations of the $K$-shell radiation spectrum from imploding wire arrays and laser-foil interaction experiments are performed using a one-dimensional collisional-radiative equilibrium ionization model with probability-of-escape radiation transport. The resulting spectra are analyzed using diagnostic techniques based on the assumption that the plasma is an isodense, isothermal emitter. It is shown that temperature determinations via line ratios and bound-free continuum slopes are affected by plasma opacity, the temperature dependence of line and continuum emission power, and the spatial ion density distribution in the plasma. Significant differences between actual and predicted values of plasma parameters are found, and the physical reasons for the discrepancies are discussed in detail.