Publications by Laurent Villard

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Global gradient driven gyrokinetic simulations performed with the Gyrokinetic Electromagnetic Numerical Experiment (GENE) code are used to investigate Tokamak a configuration variable (TCV) plasmas with negative triangularity. Considering limited L-mode pl ...

Flux-driven global gyrokinetic codes are now mature enough to make predictions in terms of turbulence and transport in tokamak plasmas. Some of the recent breakthroughs of three such codes, namely GYSELA, ORB5 and XGC1, are reported and compared wherever a ...

Modern supercomputer architectures are evolving towards embedding more and more cores per compute node, often making use of accelerators such as GPUs, in which thousands of threads can be executed concurrently. To make legacy codes profit efficiently from such resources usually requires a major refactoring effort. I will present the strategy that we adopted for the production code ORB5, a global gyrokinetic Particle-In-Cell (PIC) code for studying turbulence in tokamak plasmas, developed by many physicists

Maxwell's equations are solved in a toroidal axisymmetric plasma. The numerical method implemented in the PENN code is based on a formulation in terms of the electromagnetic potentials and a discretization with standard bilinear or bicubic Hermite finite elements. Two models for the dielectric tensor operator yield different physical problems, which can be used comparatively to study small amplitude plasma perturbations down to the Alfven range of frequencies. The first treats the plasma as resistive fluids

After a brief introduction on present day simulation and modeling of burning plasmas in magnetically confined devices, the results of a non-linear benchmark are presented, undertaken among several state-of-the-art codes available to study the self-consistent interaction of an Energetic Particle (EP) population with shear Alfv & eacute;n waves: HYMAGYC, MEGA, ORB5 and XTOR-K. The first two codes, HYMAGYC and MEGA, are hybrid codes: HYMAGYC is a MHD-Gyrokinetic code (the bulk plasma is represented by MHD equa

Using the local (flux-tube) version of the Eulerian code GENE (Jenko et al 2000 Phys. Plasmas 7 1904), gyrokinetic simulations of microturbulence were carried out considering parameters relevant to electron-internal transport barriers (e-ITBs) in the TCV t ...

The theoretical study of plasma turbulence is of central importance to fusion research. Experimental evidence indicates that the confinement time results mainly from the turbulent transport of energy, the magnitude of which depends on the turbulent state r ...

Following recent observations of unstable Toroidal Alfven Eigenmodes (TAEs) in a counter-current Neutral Beam Injection (NBI) scenario developed in TCV, an in-depth analysis of the impact of such modes on the global confinement and performance is carried o ...

An electron density gradient driven instability identified as the toroidal branch of the universal drift instability is studied using a global gyrokinetic model treating both electrons and ions fully nonadiabatically and valid at all orders in the ratio of ...

The paper presents the KINX code for computing linear ideal MHD growth rates and eigenvectors of axisymmetric plasmas surrounded by a vacuum layer and a conducting wall. Plasma equilibrium magnetic surfaces are assumed to be nested either in the whole plasma domain (separatrix at the plasma boundary is possible) or in the domains separated by an internal separatrix (doublet and divertor configurations). The computational domain is decomposed into subdomains with nested flux surfaces. In each subdomain finit

The mutual interactions of ion temperature gradient (ITG) driven modes, zonal flows and geodesic acoustic modes (GAM) in tokamak plasmas are investigated using a global nonlinear gyrokinetic formulation with totally unconstrained evolution of temperature g ...

Global Alfven eigenmodes are studied using two different models for the plasma and the results compared with the instability threshold measured experimentally. Fluid-resistive models predict that continuum damped toroidicity induced Alfven modes (TAE) are formed in the frequency range of the experimental instabilities, but using realistic values of the resistivity makes a stability analysis impossible for computational reasons. The kinetic plasma model solves this problem by taking into account the ion Larm

In this work, a Fourier solver [B.F. McMillan, S. Jolliet, A. Bottino, P. Angelino, T.M. Tran, L Villard, Comp. Phys. Commun. 181 (2010) 7151 is implemented in the global Eulerian gyrokinetic code GT5D [Y. Idomura, H. Urano, N. Aiba, S. Tokuda, Nucl. Fusio ...

It is believed that low frequency microinstabilities such as ion temperature gradient (ITG) driven modes and trapped electron modes (TEMs) are largely responsible for the experimentally observed anomalous transport via the ion and electron channels in a to ...

Electrostatic microinstabilities in ion internal barrier (ITB) and H-mode discharges of the ASDEX Upgrade tokamak [O. Gruber, R. Arslanbekov, C. Atanasiu , Nucl. Fusion 41, 1369 (2001)] have been investigated with a full radius gyrokinetic code. The code models linear stability and includes the effect of an equilibrium radial electric field and trapped electrons. In order to simulate plasmas in experimental conditions [k(perpendicular to)rho(L)similar toO(1)], the long wavelength approximation in the quasin

In the context of global gyrokinetic simulations of turbulence using a particle-in-cell framework, verifying the delta-f assumption with a fixed background distribution becomes challenging when determining quasi-steady state profiles corresponding to given ...

A new conservative gyrokinetic full-f Vlasov code is developed using a finite difference operator which conserves both the L1 and L2 norms. The growth of numerical oscillations is suppressed by conserving the L2 norm, and the code is numerically stable and ...

Scientific and technical activities on JET focus on the issues likely to affect the ITER design and operation. Our understanding of the ITER reference mode of operation, the ELMy H-mode, has progressed significantly. The extrapolation of ELM size to ITER has been re-evaluated. Neoclassical tearing modes have been shown to be meta-stable in JET, and their beta limits can be raised by destabilization (modification) of sawteeth by ion cyclotron radio frequency heating (ICRH). Alpha simulation experiments with

Plasma Turbulence studied by means of Correlation-ECE in the TEM domain in TCV Electron temperature fluctuations in the TEM domain have been measured in TCV using the correlation-ECE diagnostics [1]. Significant broadband electron temperature fluctuations are found radially extending between 0.3

The nonlinear dynamics of beta-induced Alfven eigenmodes (BAEs) driven by energetic particles (EPs) in the presence of ion-temperature-gradient turbulence is investigated, by means of selfconsistent global gyrokinetic simulations and analytical theory. A t ...

Laurent Villard

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Nonlocal effects in negative triangularity TCV plasmas

Predictions on heat transport and plasma rotation from global gyrokinetic simulations

Porting a Legacy Global Lagrangian PIC Code on Many-Core and GPU-Accelerated Architectures

Global Waves in Resistive and Hot Tokamak Plasmas

State of the Art of Gyrokinetic and Hybrid Mhd-kinetic Codes Through Non-linear Benchmarking to Study Reactor Relevant Burning Plasmas

Non-Linear Gyrokinetic Simulations of Microturbulence in TCV Electron Internal Transport Barriers

The role of plasma elongation on turbulent transport in magnetically confined plasmas

Study of fast-ion-driven toroidal Alfvén eigenmodes impacting on the global confinement in TCV L-mode plasmas

Toroidal Universal Drift Instability: A Global Gyrokinetic Study

The KINX ideal MHD stability code for axisymmetric plasmas with separatrix

Effects of plasma current on nonlinear interactions of ITG turbulence, zonal flows and geodesic acoustic modes

Stability of global drift-kinetic Alfven eigenmodes in DIII-D

Parallel filtering in global gyrokinetic simulations

A comprehensive gyrokinetic description of global electrostatic microinstabilities in a tokamak

Simulations of global electrostatic microinstabilities in ASDEX Upgrade discharges

Gyrokinetic flux-driven simulations in mixed TEM/ITG regime using a delta-f PIC scheme with evolving background

New conservative gyrokinetic full-f Vlasov code and its comparison to gyrokinetic delta f particle-in-cell code

Overview of JET results

Plasma Turbulence studied by means of Correlation-ECE in the TEM domain in TCV

Gyrokinetic investigation of Alfven instabilities in the presence of turbulence