VIRIATO

 

A Fourier-Hermite spectral code for strongly magnetised plasma dynamics

Benchmarks

Tearing mode benchmark against full Gyrokinetic code AstroGK [Numata et al., J. Comp. Phys. 229, 9347 (2010)]. VIRIATO shows very good agreement with AstroGK in the small beta limit. [The original tearing mode study used for this benchmark is reported in Numata et al., Phys. Plasmas 18, 112106 (2011)]

SCALING

VIRIATO exactly reproduces the Kinetic Alfvén Wave (KAW) dispersion relation. Figures show the frequency (left) and damping rates (right) as a function of the electron skin-depth. Data points are from VIRIATO; lines are the exact analytical solution.

Viriato was a Lusitanian hero fighting the Roman occupation.

VIRIATO is a versatile code to solve three different sets of equations:

    - The Kinetic Reduced Electron Heating Model [a.k.a. KREHM, Zocco & Schekochihin, Phys. Plasmas 18, 102309 (2011)]; this is a 4D (position plus parallel velocity) reduced gyrokinetic model, valid in the limit of low plasma beta.

    - Kinetic long wavelength slow mode eqs. [Schekochihin et al., Astrophys. J. Suppl. 182, 310 (2009)]

    - Reduced MHD [Strauss, Phys. Fluids 19, 134 (1976)]

PUBLICATIONS

The first publication resulting from VIRIATO focuses on electron heating in weakly collisional, strongly magnetised reconnection (Loureiro, Schekochihin and Zocco, Phys. Rev. Lett. 111, 025002 (2013)).  The main result is the demonstration of the dominance of Landau damping (i.e., velocity space dissipation arising from phase-mixing) over real-space dissipation as the main electron heating mechanism.

VIRIATO TEAM

VIRIATO is based on a 2D gyrofluid code originally developed by Nuno Loureiro and Bill Dorland (U. Maryland). Currently, VIRIATO is developed and maintained by Nuno Loureiro, L. Fazendeiro (IPFN), Anjor Kanekar (U. Maryland) and Alfred Mallett (U. Oxford). Other collaborators include W. Dorland (U. Maryland), R. Numata (U. Hyogo), R. Samtaney (KAUST), Alex Schekochihin (U. Oxford), A. Zocco (IPP Greifswald).

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Last update: 03/06/2013

Phase-space evolution during reconnection: progressive filamentation of the electron distribution function is observed, the textbook signature of phase-mixing.

Preliminary tests show good strong and weak scaling performance on Hopper (Cray XE6, NERSC) and Edison (Cray XC30, NERSC).

VIRIATO is pseudo-spectral (Fourier) in the xy plane and spectral (Hermite) in velocity space. Along the z (magnetic guide-field) direction, the equations are discretised on a grid and integrated using a combination of a 3rd order Total Variation Diminishing Runge-Kutta method for the time derivative with a seventh-order upwind scheme for the fluxes [R. Samtaney, Comp. Sci. Disc.  5, 014004 (2012)].

VIRIATO is written in Fortran 90 and fully parallelised using domain decomposition with MPI. FFTs are performed with the freely available package fftw.

Algorithms