Investigation of non-ideal effects in wave-heated dense microplasmas using particle-in-cell Monte Carlo-collision modeling

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2022-05-09

Authors

Solmaz, Evrim

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Abstract

Recent experiments observing the development of extreme-density plasmas led to a more careful and detailed look at assumptions made for low-density plasmas. As plasma approaches the warm dense matter regime, the physics change significantly, which necessitates novel computational methods that relax some preliminary assumptions made for low-density plasmas. One such example is the ideal plasma approximation, which is not adequately accurate at high pressures. In this dissertation, the development of a particle-in-cell Monte Carlo-collision (PIC-MCC) computational model for strongly ionized non-ideal plasmas is presented. The model is established to investigate the interaction of electromagnetic waves and dense plasmas at high pressures, and study the second-stage wave-heating that results from this interaction. The main focus is on establishing a valid plasma chemistry for extreme-density, non-ideal, strongly ionized plasmas; which differs drastically from established chemistry mechanisms for low-density plasmas. Plasma non-ideality resulting from Coulomb coupling at high plasma densities is manifested as a depression in the effective ionization potential of atoms and enhanced collision cross sections. Using a one-dimensional PIC-MCC model, full ionization of the plasma is found to occur on the picosecond timescale, with the plasma non-ideality resulting in more rapid ionization compared to an ideal plasma, especially at higher pressures. Moreover, the significance of excited states is reflected in the ionization process with a stepwise ionization reaction. This additional pathway is revealed as a very important mechanism for plasma generation that speeds up the process to reach full ionization. Next, the one-dimensional PIC-MCC model is parallelized using the shared-memory parallelization library OpenMP to increase the code performance by decreasing the run time by ~60%. Finally, the one-dimensional model is extended to two dimensions to capture geometrically more complicated discharges and their interactions with generalized electromagnetic waves.

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