Linear microstability growth rates are calculated on a wavenumber-by-wavenumber basis with an implicit initial-value algorithm in the ballooning (or "flux-tube") limit. Linear and quasilinear properties of the fastest growing (or least damped) eigenmode at a given wavenumber may be calculated independently (and therefore reasonably quickly).
Nonlinear simulations of fully developed turbulence can be performed by users with access to a parallel computer. All plasma species are treated on an equal, gyrokinetic footing. Nonlinear simulations provide fluctuation spectra, anomalous (turbulent) heating rates, and species-by-species anomalous transport coefficients for particles, momentum and energy.
GS2 is a parallel code which scales well to large numbers of processors. There are separate optimizations to work with for small (Beowulf-style) clusters and large supercomputers.
Linear and nonlinear calculations may be carried out using a wide
range of assumptions, including:
Vacuum magnetic dipole
High aspect ratio torus (analytic axisymmetric equilibrium)
Numerically generated, local equilibrium (Miller-style)
Axisymmetric, numerically generated equilibria with arbitrary poloidal shaping from
Non-axisymmetric (stellarator) equilibria from VMEC
GS2 is fully supported by the GKV suite of IDL-based diagnostics developed for gyrokinetic turbulence simulation codes. Contact William Nevins for more information. Output files are written with NetCDF.
Because it was designed according to object-oriented principles, GS2 has been kept portable without sacrificing performance. For example, all parallelism is expressed in a single communications module, which can easily be adapted to a new platform. (Presently MPI and SHMEM are supported; serial execution is also available.)
Turbulent structures in gyrokinetics are highly elongated along the magnetic field. GS2 uses field-line following (Clebsch) coordinates to resolve such structures with maximal efficiency, in a flux tube of modest extent. Pseudo-spectral algorithms are used in the spatial directions perpendicular to the field, and for the two velocity space coordinate grids (energy and pitch angle) for high accuracy on computable 5-D grids.