Improving conservation properties of a 5D gyrokinetic semi-Lagrangian code

In gyrokinetic turbulent simulations, the knowledge of some stationary states can help reducing numerical artifacts. Considering long-term simulations, the qualities of the Vlasov solver and of the radial boundary conditions have an impact on the conservation properties. In order to improve mass and energy conservation mainly, the following methods are investigated: fix the radial boundary conditions on a stationary state, use a 4D advection operator that avoids a directional splitting, interpolate with a delta-f approach. The combination of these techniques in the semi-Lagrangian code Gysela leads to a net improvement of the conservation properties in 5D simulations. (authors)