Publications by Laurent Villard

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Using a global approach for solving an ion gyrokinetic model in three-dimensional geometry the linear stability and structure of ion-temperature-gradient (ITG) modes in the configuration of the stellarator Wendelstein 7-X (W7-X) [G. Grieger , in Plasma Physics and Controlled Nuclear Fusion Research 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 525.] is studied. The time evolution of electrostatic perturbations is solved as an initial value problem with a particle-in-cell deltaf method.

Turbulence in tokamaks generates radially sheared zonal flows. Their oscillatory counterparts, geodesic acoustic modes (GAMs), appear due to the action of the magnetic field curvature. The GAMs can be driven unstable by an anisotropic energetic particle (E ...

With the term microinstabilities, we indicate a class of plasma drift waves such as the ion temperature gradient (ITG) mode, the trapped electron mode (TEM), and the electromagnetic Alfvenic ion temperature gradient (AITG) mode. They are usually driven by ...

Energy transfer from electron-cyclotron (EC) waves to the plasma is being routinely used in tokamaks to heat and drive current through the electron channel. Technical applications such as magnetohydrodynamic mode mitigation require power deposition with a ...

In this work, we explore the effects of collisions on turbulent transport, focusing on two different TCV magnetic equilibria featuring positive and negative triangularity. The investigation is conducted using gyrokinetic modeling. Both gradient-driven and ...

Gyrokinetic codes in plasma physics need outstanding computational resources to solve increasingly complex problems, requiring the effective exploitation of cutting-edge HPC architectures. This paper focuses on the enabling of ORB5, a state-of-the-art, fir ...

There is not yet a straightforward method for determining the D-T ratio in the centre of a tokamak plasma. One of the simpler measurements put forward in the past is the interpretation of the MHD spectrum in the frequency range of the global Alfven eigenmodes (GAE). However, the frequencies of these modes do not depend on the plasma mass alone, but are also quite strongly dependent on the details of the current and density profiles; this creates a problem of deconvolution of the estimate of the plasma mass

Electromagnetic turbulence is addressed in tokamak and stellarator plasmas with the global gyrokinetic particle-in-cell codes ORB5 (E Lanti et al, Comp. Phys. Comm., 251, 107072 (2020)) and EUTERPE (V Kornilov et al, Phys. Plasmas, 11, 3196 (2004)). The la ...

The particle-in-cell code ORB5 is a global gyrokinetic turbulence simulation code in tokamak geometry. It has been developed at CRPP, Lausanne, Switzerland, with major contributions from IPP, Garching, Germany, and IPP, Greifswald, Germany, under a long-st ...

Low aspect ratio tokamaks (LATs) can potentially provide a high ratio of plasma pressure to magnetic pressure beta and high plasma current I at a modest size. This opens up the possibility of a high-power density compact fusion power plant. For the concept to be economically feasible, bootstrap current must be a major component of the plasma current, which requires operating at high beta(p). A high value of the Troyon factor beta(N) and strong shaping is required to allow simultaneous operation at a high-P

We consider the communication costs of gyrokinetic plasma physics simulations running at large scale. For this we apply virtual decompositions of the toroidal domain in three dimensions and additional domain cloning to existing simulations done with the OR ...

Global simulations of electromagnetic turbulence in circular-flux-surface tokamak and ASDEX-Upgrade geometry, tearing instabilities and their combination with the electromagnetic turbulence, nonlinear Alfvenic modes in the presence of fast particles and th ...

Research on the Tokamak à Configuration Variable (TCV) addresses a wide range of key questions relevant to ITER and future fusion power plants. Over the past two years, highly productive experimental campaigns have led to major advances across several areas: the ITER baseline scenario; pedestal properties in low-collisionality, peeling-limited conditions; and the development of high-

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, non-inductive regimes. Alternative high-confinement scenarios have likewise received significant attention, with re

Gyrokinetic simulations are computationally extremely demanding due to the high dimensionality of the physical phase space and the interplay between plasma particles and electromagnetic fields. It is thus essential to make full use of the available numerical resources to be able to simulate more complex physical problems. With the aim of optimizing the gyrokinetic Particle-In-Cell code ORB5 towards exascale computing, a particle sorting method is implemented to increase data locality. Furthermore, different

A new code is presented here, named Gyrokinetic SEmi-LAgragian (GYSELA) code, which solves 4D drift-kinetic equations for ion temperature gradient driven turbulence in a cylinder (r, theta, z). The code validation is performed with the slab ITG mode that o ...

Global Alfven eigenmodes are studied using fluid and kinetic plasma models to determine how the finite Larmor excursions of the bulk species and the resonant Landau interactions modify the spectrum in the toroidicity Alfven eigenmode (TAE) range of frequencies. A new kinetic Alfven mode conversion mechanism is described taking place away from the resonances through toroidal coupling, when the spatial scales of the fast and the kinetic Alfven waves become comparable. If the Landau damping of the mode convert

A new solver for Maxwell's equations in three-dimensional (3D) plasma configurations is presented. The new code LEMan (Low-frequency ElectroMagnetic wave propagation) determines a global solution of the wave equation in a realistic stellarator geometry at ...

Experiments on the TCV tokamak have shown that rapid vertical movement of diverted ELMy H-mode plasmas can affect the time sequence of edge localized modes. The effect is attributed to the induction of an edge current during the movement of the plasma column in the spatially inhomogeneous vacuum field of a single-null configuration. In TCV the fast vertical movement is provoked by the positional control coils inside the vacuum vessel, however it is argued that a similar effect might be produced in larger de

Collisionless delta-f gyrokinetic particle-in-cell simulations suffer from the entropy paradox, in which the entropy grows linearly in time while low-order moments are saturated. As a consequence, these simulations do not reach a steady state and are unsui ...

Strong electric fields generate an ExB rotation of the equilibrium plasma. Experiments have shown that this effect could lower the anomalous transport in tokamaks. The study of the effect of these flows on the linear stability of ion temperature gradient (ITG) modes has therefore been undertaken. The question is addressed solving the spectrum of the gyrokinetic equation in the full two-dimensional poloidal plane for a large aspect ratio tokamak with concentric circular magnetic surfaces. Results show a stro

Laurent Villard

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Gyrokinetic global three-dimensional simulations of linear ion-temperature-gradient modes in Wendelstein 7-X

Nonlinear dynamics of energetic-particle driven geodesic acoustic modes in ASDEX Upgrade

A spectral global gyrokinetic approach to plasma linear microinstability analysis

Experimental and numerical investigations of electron transport enhancement by electron-cyclotron plasma-wave interaction in tokamaks

Collisional effects on positive and negative triangularity through local and global temperature gradient-driven and flux-driven gyrokinetic simulations

Gyrokinetic simulations on many- and multi-core architectures with the global electromagnetic Particle-In-Cell Code ORB5

Measurement of the effective plasma ion mass in large tokamaks using global Alfven eigenmodes

Numerics and computation in gyrokinetic simulations of electromagnetic turbulence with global particle-in-cell codes

Global Nonlinear Electromagnetic Simulations of Tokamak Turbulence

Stable equilibria for bootstrap-current-driven low aspect ratio tokamaks

Prediction of the Inter-Node Communication Costs of a New Gyrokinetic Code with Toroidal Domain

Gyrokinetic particle-in-cell simulations of electromagnetic turbulence in the presence of fast particles and global modes

Progress and innovations in the TCV tokamak research programme

Hybrid OpenMP/MPI parallelization of the charge deposition step in the global gyrokinetic Particle-In-Cell code ORB5

A drift-kinetic Semi-Lagrangian 4D code for ion turbulence simulation

Kinetic Alfvén eigenmodes in a hot tokamak plasma

A full-wave solver of the Maxwell's equations in 3D cold plasmas

Magnetic triggering of ELMs in TCV

Quasi-steady and steady states in global gyrokinetic particle-in-cell simulations

Effect of E x B flows on global linear ion temperature gradient modes