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.