Parallel filtering in global gyrokinetic simulations

In this work, a Fourier solver [McMillan et. al., Comput. Phys. Commun. 181, 715 (2010)] is implemented in the global Eulerian gyrokinetic code GT5D [Y. Idomura et. al., Nucl. Fusion 49, 065029, 2009] and in the global Particle-In-Cell code ORB5 [S. Jolliet et. al., Comput. Phys. Commun 177, 477 (2007)] in order to reduce the memory of the matrix associated with the field equation. This scheme is verified with linear and nonlinear simulations of turbulence. It is demonstrated that the straight-field-line angle is the coordinate that optimizes the Fourier solver, that both linear and nonlinear turbulent states are unaffected by the parallel filtering, and that the k‖ spectrum is independent of plasma size at fixed normalized poloidal wave number.