  De-aliasing is an essential procedure for eliminating the aliasing error in
nonlinear simulations, such as nonlinear gyrokinetic turbulence simulations. An
ideal approach to de-aliasing in the periodic dimension is Fourier truncation.
Finite difference low-pass filtering applied in the non-periodic direction
strongly dampens aliasing modes. At the same time, it induces numerical
dissipation in the region of the physically realistic solution. It is shown
analytically that the long-wave dissipation coefficient is proportional to the
(Np-3) power of the wavenumber under desirable constraints satisfying the
highest order accuracy, where Np is the number of filter points. Numerical
results after applying the optimised low-pass filtering to the nonlinear
gyrokinetic turbulence simulation suggest that the nine-point format preserves
intact mesoscopic zonal structures in Tokamak plasmas, and is therefore
suitable for long-time nonlinear turbulence simulations.
