Momentum Diffusivity Estimation via PDE-Constrained Optimization
C. Xu, Y. Ou, E. Schuster, J. Ferron, T.C. Luce, M.L. Walker, D.A. Humphreys, T.A. Casper, W.H. Meyer
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
Dallas, Texas, November 17-21, 2008
Abstract
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Several experiments around the world have demonstrated that plasma
rotation can improve plasma stability and enhance confinement. It has
been shown [1] that the critical rotation speed for stabilization is a
function of the rotation profile shape, implying a radially distributed
stabilizing mechanism. Modeling of the rota- tional profile dynamics
is limited by poor knowledge of the momentum diffusivity coefficient.
In this work we use toroidal angular velocity data from experiments
where the torque is modulated using neutral beams, and we employ
optimization techniques to estimate the momentum diffusivity
coefficient for the angular momen- tum partial differential equation
(PDE) that best fits the experimental data. To further investigate the
nonlinear dependence of the momentum diffusivity on other physical
variables such as temperatures and densities, we introduce techniques
from nonlinear regression and machine learning.
[1] A.C. Sontag, et al., Nucl. Fusion 47, 1005 (2007).