Abstract of VIRIATO Project

This proposal aims at improving the I/O capability of the code Viriato, a unique framework that solves a reduced (4D, instead of the usual 5D) version of gyrokinetics applicable to strongly magnetised plasmas. Viriato is fully parallelized, using domain decomposition with MPI; it is pseudo-spectral perpendicular to the magnetic field and employs a high order upwind scheme for discretizing the equations along the magnetic field. A distinguishing feature of the code is its use of a spectral representation (Hermite polynomials) to handle the velocity space dependence. This Hermite representation converts a drift-kinetic equation for the electrons into a coupled set of fluid-like equations for each of the coefficients of the Hermite polynomials. In terms of numerical accuracy this is rather advantageous, since spectral representations are more powerful that grid-based ones, and it enables the deployment of the standard tools of CFD to deal with what would otherwise be a difficult kinetic equation.

In 2015 Viriato was the recipient of HLST support which focused on the optimization of the code's parallel performance. The project is still ongoing although preliminary results already show a very good improvement in scalability. This made us realize that the main bottleneck, in order resolve more accurately electron-scale physics, in problems such as kinetic plasma turbulence, magnetic reconnection and the electron temperature gradient instability, was the (parallel) I/O performance of the code, whose optimization is the main goal of this project.