Abstract
A finite-difference scheme, with appropriate nonuniform grid correction, is used to solve two-dimensional (2-D) Fokker-Planck equations in velocity space for several scenarios pertaining to lower-hybrid (LH) and electron cyclotron (EC) current drive (CD) in tokamak plasmas. The aim is to assess how nonuniform grids perform in reducing the computational costs of typical Fokker-Planck calculations, whilst keeping the accuracy in the computed rf current and absorbed power densities within reasonable limits. To achieve this goal, the parameters that enable one to define a specific nonuniform grid are explored, more precisely, the grid spacings within each distinct region of the 2-D (speed and pitch angle) velocity space. The results are shown as plots of the estimated savings in computational effort, as well as of the relative errors in the current and power densities, against the nonuniform-grid parameters under analysis. Several features exhibited by such results (which may be found useful when establishing rules for designing nonuniform grids) are also discussed, both for LHCD and ECCD.
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