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Title:  A STUDY OF TURBULENCEDRIVEN INWARD MOMENTUM FLUX & CONSTRUCTION OF A DIFFERENCE SCHEME FOR FOKKERPLANCKLANDAU OPERATOR 
Authors:  Yoon, Eisung 
Advisors:  Hahm, T.S. Chang, C.S. 
Contributors:  Plasma Physics Department 
Subjects:  Plasma physics 
Issue Date:  2013 
Publisher:  Princeton, NJ : Princeton University 
Abstract:  Momentum transport driven by microinstability is studied via analytic theories, gyrokinetic simulations, and experimental data analysis. A scenario for rotation profile evolution is constructed based on experimental observation that parallel flow initiates at edge region and penetrates into core region of tokamak [1]. In particular, turbulent diffusion and inward convective pinch are studied according to this scenario. For study of convective momentum pinch, toroidal ion temperature gradient mode near marginal stability is examined in kinetic limit. It is found from quasilinear estimation that the inward turbulent equipartition momentum pinch remains as the most robust part of pinch. In addition, it is found that ion temperature gradient driven momentum pinch is inward for typical parameters, while ion density gradient driven momentum pinch is outward. It is shown by theoretical formulas and experimental data analysis that momentum pinch velocity is sensitive to the electron to ion temperature ratio. For study of diffusive momentum transport, parallel shear flow instability is studied in fluid limit. Diffusion coefficient using mixing length estimate from nonlocal theory reveals that it has a strong dependence on the parallel flow shear and is mainly carried by fluctuations in short wavelength regime. Gyrokinetic simulation of collisionless parallel shear flow instability shows that the analytic prediction of diffusion coefficient is comparable to numerical values in the linear phase of the simulations. In the nonlinear phase, fluctuation energy gets transferred to the long wavelength regime.
A twodimensional, uniform velocitygrid based solver for the nonlinear FokkerPlanckLandau (FPL) collision operator has been developed in the limit of strong magnetic field. The conservative and entropy increasing semidiscretized numerical scheme for the isotropic FPL equation by C. Buet et al. (2002) has been extended to 2D velocity space. A Picard fixed point method is used for semiimplicit time advance. One time evaluation of interpolation coefficients for probability distribution function is introduced so that numerical equilibrium is achieved with Maxwellian. However, positivity property is sacrificed at the saving of computational costs. In addition, a highly practical method is suggested to apply the velocitygrid based collision solver to particleincell code. 
URI:  http://arks.princeton.edu/ark:/88435/dsp018336h201n 
Alternate format:  The Mudd Manuscript Library retains one bound copy of each dissertation. Search for these copies in the library's main catalog: http://catalog.princeton.edu/ 
Type of Material:  Academic dissertations (Ph.D.) 
Language:  en 
Appears in Collections:  Plasma Physics

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