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 Title
 Computational study of strongly coupled charged particle systems
 Creator
 Dharuman, Gautham
 Date
 2018
 Collection
 Electronic Theses & Dissertations
 Description

Exciting experiments in ultracold neutral plasmas, lasermatter interaction, charged particle stopping, mixing under extreme conditions etc., at academic facilities or at even larger facilities such as the National Ignition Facility, Z machine or the Linac Coherent Light Source, have necessitated the need for models that can simulate these systems at large length and timescales. This thesis summarizes my research work, falling within the category of computational plasma physics, aimed at...
Show moreExciting experiments in ultracold neutral plasmas, lasermatter interaction, charged particle stopping, mixing under extreme conditions etc., at academic facilities or at even larger facilities such as the National Ignition Facility, Z machine or the Linac Coherent Light Source, have necessitated the need for models that can simulate these systems at large length and timescales. This thesis summarizes my research work, falling within the category of computational plasma physics, aimed at three aspects: effective quantum potentials based method for nonequilibrium quantum electron dynamics at scale, efficient force calculation method for molecular dynamics simulation with screened Coulomb interactions, and an avenue based on compressed gases for creation of laboratoryscale tunable strongly coupled plasmas as a platform for understanding largescale experiments. Effective classical dynamics provide a potentially powerful avenue for modeling largescale dynamical quantum systems. We have examined the accuracy of a Hamiltonianbased approach that employs effective momentumdependent potentials (MDPs) within a moleculardynamics framework through studies of atomic ground states, excited states, ionization energies and scattering properties of continuum states. Working exclusively with the KirschbaumWilets (KW) formulation with empirical MDPs [C. L. Kirschbaum and L. Wilets, PRA 21, 834 (1980)], leads to very accurate groundstate energies for several elements (e.g., N, F, Ne, Al, S, Ar and Ca) relative to HartreeFock values. The KW MDP parameters obtained are found to be correlated, thereby revealing some degree of transferability in the empirically determined parameters. We have studied excitedstate orbits of electronion pair to analyze the consequences of the MDP on the classical Coulomb catastrophe. From the groundstate energies, we find that the experimental first and secondionization energies are fairly well predicted. Finally, electronion scattering was examined by comparing the predicted momentum transfer cross section to a semiclassical phaseshift calculation; optimizing the MDP parameters for the scattering process yielded rather poor results, suggesting a limitation of the use of the KW MDPs for plasmas. Efficient force calculation methods are needed for molecular dynamics simulation with mediumrange interactions. Such interactions occur in a wide range of systems, including chargedparticle systems with varying screening lengths. We generalize the Ewald method to charged systems described by interactions involving an arbitrary dielectric response function. We provide an error estimate and optimize the generalization to find the breakeven parameters that separate a neighbor listonly algorithm from the particleparticle particlemesh (PPPM) algorithm. We examine the implications of different choices of the screening length for the computational cost of computing the dynamic structure factor. We then use our new method in molecular dynamics simulations to compute the dynamic structure factor for a model plasma system and examine the wavedispersion properties of this system. Laboratoryscale nonideal plasmas with controllable properties over a wide range of densities below solid density are needed for understanding largescale plasma experiments. Based on a suite of molecular dynamics simulations, we propose a general paradigm for producing such controllable nonideal plasmas. We simulated the formation of nonequilibrium plasmas from photoionized, cool gases that are spatially precorrelated through neutralneutral interactions that are important at moderate to high pressures. We examined the plasmaformation process over ordersofmagnitude variations in the initial gas pressure to characterize variations in several physical properties, including Coulomb collisional rates, partial pressures, screening strengths, continuum lowering, interspecies Coulomb coupling, electron degeneracy and ionization states. We find that variations in the initial gas pressure lead to controllable variations in a wide range of plasma properties, including the equation of state, collisional processes, atomic processes and basic plasma properties (coupling, screening and degeneracy). This paradigm has significant advantages over soliddensity experiments because the collisional, collective and recombination timescales are reduced by a factor of 3 to 10, potentially broadening the efficacy of diagnostics. The paradigm also has advantages over ultracold plasma experiments because the trapping and cooling phases are avoided.
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 Title
 Segmented nanoforce sensor
 Creator
 Dharuman, Gautham
 Date
 2013
 Collection
 Electronic Theses & Dissertations
 Description

Nanoscale force sensors are finding widespread applications in atomic and biological force sensing where forces involved range from zeptonewtons to several nanonewtons. Different methods of nanoscale force sensing based on optical, electrical or purely mechanical schemes have been reported. However, each technique is limited by factors such as large size, low resolution, slow response, force range and alignment issues. In this research, a new device structure which could overcome the above...
Show moreNanoscale force sensors are finding widespread applications in atomic and biological force sensing where forces involved range from zeptonewtons to several nanonewtons. Different methods of nanoscale force sensing based on optical, electrical or purely mechanical schemes have been reported. However, each technique is limited by factors such as large size, low resolution, slow response, force range and alignment issues. In this research, a new device structure which could overcome the above mentioned constraints is studied theoretically and experimentally for the possibility of its application in nanoscale force sensing.
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