Viriato: A Fourier-Hermite spectral code for strongly magnetized fluid-kinetic plasma dynamics

Viriato is a novel fluid–kinetic code that solves a reduced-gyrokinetic set of equations [the Kinetic Reduced Electron Heating Model (KREHM) equations, which reduce to the standard Reduced-MHD equations in the appropriate limit]. Two main applications of these equations are magnetized (Alfvénic) plasma turbulence and magnetic reconnection. Viriato uses operator splitting (Strang or Godunov) to separate the dynamics parallel and perpendicular to the ambient magnetic field (assumed strong). Along the magnetic field, Viriato allows for either a second-order accurate MacCormack method or, for higher accuracy, a spectral-like scheme composed of the combination of a total variation diminishing (TVD) third order Runge–Kutta method for the time derivative with a 7th order upwind scheme for the fluxes. Perpendicular to the field Viriato is pseudo-spectral, and the time integration is performed by means of an iterative predictor–corrector scheme. In addition, a distinctive feature of Viriato is its spectral representation of the parallel velocityspace dependence, achieved by means of a Hermite representation of the perturbed distribution function. This talk will briefly describe the physics model and the main algorithms employed in the code. A set of linear and nonlinear benchmarks will be presented. Lastly, we will illustrate the advantages of the Hermite formulation by highlighting recent results on reconnection and turbulence that were obtained with Viriato.