Physics

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    A NEW HOPE: CAN WE PREDICT GEODYNAMO DYNAMICS?
    (2022) Perevalov, Artur; Lathrop, Daniel; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The Earth’s magnetic field is hugely important, as it protects the surface of the planet from cosmic radiation and charged particles coming from the Sun and enables navigation for many living species. However, how it is generated and why it changes its value and configuration in time is poorly understood. The leading theory for the generation of the Earth’s magnetic field is the geodynamo: an electrically conductive fluid in the Earth’s core creates and maintains a magnetic field over an astronomical time scale.To probe this theory experimentally, the Three Meter Experiment—a 3 meter diameter spherical-Couette apparatus—was built to model the Earth's core. The experiment consists of two rotating concentric spheres with liquid sodium between them. The rotating spheres generate fluid motion and reproduce the dynamics similar to those that occur in the planet's core. The previous generation of the experiment was not able to generate a self-sustaining magnetic field. However, numerical studies suggest that increasing the roughness of the liquid to the solid boundary should allow enable entering the dynamo regime. To test this, we first built a scaled-down model of the Three Meter sodium experiment. This was a 40-cm water experiment to examine the increase in helicity of the flow from installing baffles on the inner sphere. We then drained 12 tons of liquid sodium from the Three Meter experiment, cleaned, fixed, and upgraded it with baffles to increase surface roughness. We then re-filled the Three Meter experiment with sodium and performed several experiments. Here, we present the results of studying the torque scaling in the experiment. We show that the experiment's highest Reynolds number is limited by the maximum torque and power in the driving motors. We further investigate the magnetic data from various experiments and show that we are likely on the edge of the dynamo action. We present observation of traveling magneto-Coriolis modes and analyze their dynamics in different conditions. These structures are important for understanding some changes in celestial objects' magnetic fields and their mechanical properties. We also present a software tool developed to mimic the observed behavior of this magnetohydrodynamic experiment. This gives us a proper tool to predict the near future of dynamos, and allows us take a deeper look into its internal structure.
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    Collective phenomena in granular and atmospheric electrification
    (2015-07-29) Nordsiek, Freja; Lathrop, Daniel
    This repository contains data from the Granular Electrification Experiment in the University of Maryland Nonlinear Dynamics Lab. The experiment consists of a cylindrical cell with aluminum plates on the top and bottom. The cell is filled with granular particles and shaken vertically for several cycles. The vertical position of the cell and the electric potential between the top and bottom endplates of the cell are acquired. The data in this repository is from experiments in which the cylindrical cell is filled with only one type of particle. One exception uses two types of particles, pointed out below. A particle type is comprised of its material, form (spheres or powder), and size range. The acceleration timeseries of the shaking is approximately a square wave with amplitude a, meaning that the vertical position is approximately a sequence of parabolas of alternating concavity. The stroke-length of the oscillation is 10.0 cm. The shaking strength is quantified as a/g where g is the free fall acceleration due to gravity on Earth. The amount of particles is quantified by the dimensionless parameter lambda = 2 N_p d^2 / (3 D^2) where N_p is the number of particles, d is the particle diameter (or effective diameter), and D is the diameter of the cell.
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    Synchronization of Network Coupled Chaotic and Oscillatory Dynamical Systems
    (2013) Barlev, Gilad Samuel; Ott, Edward; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    We consider various problems relating to synchronization in networks of coupled oscillators. In Chapter 2 we extend a recent exact solution technique developed for all-to-all connected Kuramoto oscillators to certain types of networks by considering large ensembles of system realizations. For certain network types, this description allows for a reduction to a low dimensional system of equations. In Chapter 3 we compute the Lyapunov spectrum of the Kuramoto model and contrast our results both with the results of other papers which studied similar systems and with those we would expect to arise from a low dimensional description of the macroscopic system state, demonstrating that the microscopic dynamics arise from single oscillators interacting with the mean field. Finally, Chapter 4 considers an adaptive coupling scheme for chaotic oscillators and explores under which conditions the scheme is stable, as well as the quality of the stability.
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    Calculation of Realistic Charged-Particle Transfer Maps
    (2007-10-28) Mitchell, Chad Eugene; Dragt, Alex; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The study and computation of nonlinear charged-particle transfer maps is fundamental to understanding single-particle beam dynamics in accelerator devices. Transfer maps for individual elements of the beamline can in general depend sensitively on nonlinear fringe-field and high-multipole effects. The inclusion of these effects requires a detailed and realistic model of the interior and fringe magnetic fields, including knowledge of high spatial derivatives. Current methods for computing such maps often rely on idealized models of beamline elements. This Dissertation describes the development and implementation of a collection of techniques for computing realistic (as opposed to idealized) charged-particle transfer maps for general beamline elements, together with corresponding estimates of numerical error. Each of these techniques makes use of 3-dimensional measured or numerical field data on a grid as provided, for example, by various 3-dimensional finite element field codes. The required high derivatives of the corresponding vector potential A, required to compute transfer maps, cannot be reliably computed directly from this data by numerical differentiation due to numerical noise whose effect becomes progressively worse with the order of derivative desired. The effect of this noise, and its amplification by numerical differentiation, can be overcome by fitting on a bounding surface far from the axis and then interpolating inward using the Maxwell equations. The key ingredients are the use of surface data and the smoothing property of the inverse Laplacian operator. We explore the advantages of map computation using realistic field data on surfaces of various geometry. Maps obtained using these techniques can then be used to compute realistically all derived linear and nonlinear properties of both single pass and circular machines. Although the methods of this Dissertation have been applied primarily to magnetic beamline elements, they can also be applied to electric and radio-frequency beamline elements.