Parallel filtering in global gyrokinetic simulations

In this work, a Fourier solver [B.F. McMillan, S. Jolliet, A. Bottino, P. Angelino, T.M. Tran, L Villard, Comp. Phys. Commun. 181 (2010) 7151 is implemented in the global Eulerian gyrokinetic code GT5D [Y. Idomura, H. Urano, N. Aiba, S. Tokuda, Nucl. Fusion 49 (2009) 0650291 and in the global Particle-In-Cell code ORB5 [S. Jolliet, A. Bottino, P. Angelino, It Hatzky. T.M. Iran, B.F. McMillan, O. Sauter, K. Appert, Y. Idomura, L Villard, Comp. Phys. Commun. 177 (2007) 4091 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(parallel to) spectrum is independent of plasma size at fixed normalized poloidal wave number. (C) 2011 Elsevier Inc. All rights reserved.