X-ray Heating and Temperature in Multielement Laboratory Photoionized Plasmas*

Photoionized plasmas in the universe consist of multiple elements. The mixture of elements is dominated by hydrogen while other elements are present in smaller concentrations. Yet, the heavy elements play a critical role in the dynamics and observations of these astrophysical plasmas. We present modeling and experimental results for neon-hydrogen laboratory photoionized plasmas in which the composition is dominated by hydrogen. The simulations predict that a small amount of neon has a dramatic effect on the x-ray heating of the plasma as is evidenced by the electron temperature. The experiments were performed at the Z facility of Sandia National Laboratories where a gas cell filled with neon and hydrogen was driven by the broadband x-ray flux produced by a wire array z-pinch implosion. The x-ray flux was employed in two different ways. First, to produce and sustain the photoionized plasma. Second, as a backlight for transmission spectroscopy used to diagnose the charge state distribution and extract the electron temperature from a Li-like neon population ratio. We discuss the temperature obtained from a series of experiments for multiple concentration ratios of neon and hydrogen and interpret the results with the aid of radiation-hydrodynamic simulations.