  Turbulence simulation codes can exploit the flute-like nature of plasma
turbulence to reduce the effective number of degrees of freedom necessary to
represent fluctuations. This can be achieved by employing magnetic coordinates
of which one is aligned along the magnetic field. This work presents an
approach in which the position along the field lines is identified by the
toroidal angle, rather than the most commonly used poloidal angle. It will be
shown that this approach has several advantages. Among these, periodicity in
both angles is retained. This property allows moving to an equivalent
representation in Fourier space with a reduced number of toroidal components.
It will be shown how this duality can be exploited to transform conventional
codes that use a spectral representation on the magnetic surface into codes
with a field-aligned coordinate. It is also shown that the new approach can be
generalised to get rid of magnetic coordinates in the poloidal plane
altogether, for a large class of models. Tests are carried out by comparing the
new approach with the conventional approach employing a uniform grid, for a
basic ion temperature gradient (ITG) turbulence model implemented by the two
corresponding versions of the ETAI3D code. These tests uncover an unexpected
property of the model, that localized large parallel gradients can
intermittently appear in the turbulent regime. This leaves open the question
whether this is a general property of plasma turbulence, which may lead one to
reconsider some of the usual assumptions on micro-turbulence dynamics.
