|[ home ]|
Main thrust of the GENE development for stellarator applications is the
extension of the original local model (based on the 'flux-tube' concept) toward the
flux-surface model, covering an entire stellarator surface (of infinitesimal radial extent)
per simulation. The importance of this approach lies in the fact that, in a non-axisymmetric configuration,
the individual flux-tubes usually have measurably different properties regarding
micro-instabilities and the associated turbulence.
The following picture depicts the electrostatic rms-density fluctuations caused by ITG turbulence on one W7-X toroidal period (left, the unwrapped surface). Note that the fluctuations reside mainly along a thin band on the outboard side of the configuration.
This feature is in stark contrast to the tokamak case (shown below), where strong fluctuations are present all over the outboard side, where curvature is unfavorable. It should be noted that the variation of the fluctuation amplitude is much smaller in the axisymmetric configuration that in W7-X.
The following movie shows the time evolution of the ITG density fluctuations on a W7-X magnetic surface.