SUBJECT: M.S. Thesis Presentation
BY: Min-hee Sayer
TIME: Tuesday, November 6, 2012, 1:30 p.m.
PLACE: Boggs, 3-47
TITLE: Evolution of radial force balance and radial particle transport over a L-H transition
COMMITTEE: Dr. Weston M. Stacey, Chair (NRE)
Dr. Bojan Petrovic (NRE)
Dr. Dingkang Zhang (NRE)


In operation of a tokamak experiment, the plasma confinement directly relates to performance of a fusion reactor. The plasma confinement condition generally changes from L-mode (low quality confinement) to H-mode (high quality confinement). Comparison of experimental data exhibits various distinctions between confinement modes. One noteworthy distinction between confinement modes is development of steep density and temperature gradients of electrons and ions in the plasma edge region of High confinement, H-modes, relative to Low-confinement, L-modes. The fundamental reason for the change for L-mode to H-mode is not understood. A recent study suggests that the major difference between L-mode and H-mode are associated with the electromagnetic forces in the “pinch velocity” and the pressure gradient, not in the diffusion coefficients that multiplies the pressure gradient. The research examines in detail the time evolution of the radial force balance and the particle and energy transport during the L-H transition. For the analysis, DIII-D shot #118897 is selected for transition between L- and H-mode confinements. Plasma conditions in L-mode, near the L-H transition and following the transition are selected for analysis of various parameter profiles. The initial analysis is based on the four principal equations for plasma: particle balance, momentum balance, force balance and heat conduction. Based on these equations, specific equations have been derived: toroidal and radial momentum balances, diffusion coefficient, pinch velocity and heat conduction relation for calculation of parameters. The analysis of these equations, using the measured data, establish how various terms in the radial force balance (radial electric field, VXB (electromagnetic) force, and pressure gradient) and the diffusive transport coefficients evolve over the confinement mode transition.