Finite element modelling of weak plasma turbulence (Q1263492)

The quasilinear theory, the lowest order nonlinear theory of plasma turbulence is nowadays one of the most consolidated and useful theoretical tools for the investigation of several important problems in the domain of controlled nuclear fusion research. Our study is based on ADLER, a finite element code designed to solve the quasilinear equations in two dimensions in velocity and wave number space. Special attention is paid to the algebraic solver, which was found to be the computationally most intensive section of the code. In particular we have compared the direct Gauss elimination technique with a series of vectorized iterative solvers developed at ECSEC. This comparison shows that the iterative solvers do perform successfully and, apart from the obvious savings of storage, they also prove advantageous from the viewpoint of CPU costs especially when the grid resolution is augmented. Finally, some new application of ADLER in the domain of unsteady lower hybrid current drive are presented. A good qualitative agreement with the experimental result is found, showing once more that quasilinear theory is an appropriate tool for the description of the current drive physics.