Measurement and modeling of electron temperature in laboratory photoionized plasmas

The electron temperature of laboratory photoionized plasmas characterizes the thermalization of photoelectrons, impacts charge state distribution, emissivity and opacity through atomic recombination processes, and must be understood to perform detailed comparisons with theory and modeling calculations. The neon photoionized plasma gas cell experiment at Sandia's Z machine is an established platform where systematic temperature measurements have been performed for a range of ionization parameters using a novel method [1]. We discuss the temperature measurements and compare with 1D model calculations done with different theory approximations and codes. These included a radiation-hydrodynamics simulation of the experiment performed with the HeliosCR code, and two non-equilibrium heating models that tracked the evolution of the internal energy of the electrons performed with Cretin and the astrophysical Cloudy codes. Furthermore, Cretin and Cloudy calculations were performed assuming both steady-state and time-dependent approximations. The time-history of steady-state results correlates with that of the x-ray flux while that of the time-dependent results is qualitatively and quantitatively different. All time-dependent model calculations, including HeliosCR, compared better with the measurements, which points out the importance of transient effects in the experiment and the need for time-resolved measurements. [1] R. C. Mancini et al Phys. Rev. E 101, 051201(R) (2020).