Measurement and Modeling of Temperature and Charge State Distribution in Laboratory Photoionized Plasmas
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Authors
Rowland, Jeffrey
Issue Date
2024
Type
Dissertation
Language
en_US
Keywords
Laboratory astrophysics , Photoionized plasmas , plasma
Alternative Title
Abstract
The central focus of this work aims to extract the essence of the time-dependent response in the temperature and ionization behaviour of a laboratory photoionized plasma in response to a short, intense broadband x-ray pulse. The application of astrophysical simulations to laboratory experiments is a central goal, and the previous work has identified a stark inaccuracy in the temperature with an overestimation found with Cloudy and XSTAR of a factor of two. We find that the nature of this overestimation is strongly related to the transient effect of the radiation drive, when this is accounted for the overestimation drops significantly. This is supported by the characteristic timescale for the temperature simulated with the radiation-hydrodynamics code HeliosCR and in Cretin. Further, we find that the specific atomic model considerations and detail of Cloudy, the two-level model and the corresponding lack of a detailed treatment of excited state populations, are responsible for the remaining overestimation in the temperature of the time-dependent model relative to experiment. The ionizations across the suite of steady state and time-dependent models developed in Cloudy, Cretin, and PrismSPECT are compared with data, both time-integrated charge state distributions and time-dependent Li-like and H-like neon populations. For the charge state distribution, across the set of 9 experimental instances of ionization parameter, we find no model consistent with the data in all cases. When the temperature is held constant to the solution of the time-dependent model, and only the atomic kinetics is varied between steady state and time-dependent, we find that the each code indicates the presence of a transient effect in the atomic kinetics that is independent of the effect in the temperature. The transient effect in the atomic kinetics is supported by the characteristic timescales obtained with time-dependent data and consistent with the simulated population timescales. The transient effects intrinsic to the photoionized neon gas cell experiment on Z have inspired a successor, the photoionized expanding foil experiment on OMEGA EP. This venture seeks to produce the first steady state photoionized silicon plasma created in the laboratory, and we will show that this has been achieved. The plasma is diagnosed over many lines of sight using emission and transmission spectroscopy, and the VISAR interferometer, providing measurements of the sample expansion, charge state distribution, temperature, and driving radiation flux. We report initial comparisons of the transmission measurement with Cloudy and XSTAR steady state models. The success of this experiment has provided the motivation to field a platform for the photoionization of iron at the National Ignition Facility.