Publications by Laurent Villard

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.

The wave structures, eigenfrequencies and damping rates of toroidicity and ellipticity induced Alfven eigenmodes (TAEs, EAEs) of low toroidal mode numbers (n) are calculated for various axisymmetric ideal MHD equilibria with the global wave finite element code LION. The importance of the safety factor (q) and density (rho) profiles on the continuum damping rates is analysed. For realistic profiles, several continuum gaps exist in the plasma discharge. Frequency misalignment of these gaps yields continuum da

Nonlinear electrostatic global gyrokinetic simulations of collisionless ion temperature gradient (ITG) turbulence and ExB zonal flows in axisymmetric toroidal plasmas are examined for different choices of the initial distribution function. Using a local Ma ...

A two-fold analysis of electromagnetic core tokamak instabilities in the framework of the gyrokinetic theory is presented. First principle theoretical foundations of the gyrokinetic theory are used to explain and justify the numerical results obtained with ...

Relying on the good agreement observed between the gyrokinetic PENN model and the low toroidal mode number n damping measurements from JET, the stability of Alfven eigenmodes (AEs) is predicted for reactor relevant conditions. Full non-local wave-particle power transfers are computed between global wavefields and alpha particles in an ITER reference equilibrium, showing that low-n eigenmodes (n similar or equal to 2) are strongly damped and intermediate-n eigenmodes (n similar or equal to 12) with a global

Alfven eigenmodes (AEs) with intermediate toroidal mode numbers are modelled using the global gyrokinetic PENN code to determine the stability of high performance tokamak discharges in the presence of energetic particles. A large plasma pressure and a weak magnetic shear in the core give rise to radially extended kinetic AEs, which are stabilized by the high shear at the edge of a divertor (X point) configuration. Large values for the safety factor and the ion Larmor radius in reversed shear operation may h

In order to address non-local effects in turbulent transport of magnetic-fusion devices, the gyrokinetic code GENE has been extended from a flux tube to a more global geometry. This global version of GENE includes radial variations of temperature and density profiles, as well as of magnetic equilibrium quantities. Non-periodic radial boundary conditions allow for profile evolution. Thanks to an interface with the MHD equilibrium code CHEASE, as well as the implementation of various types of source and sink

Kinetic effects have been implemented in the three-dimensional full-wave code LEMan. These allow modeling Landau damping as well as the Kinetic Alfvén Wave (KAW). Special attention has been taken on the exact computation of the parallel wave vector as it c ...

The scaling of turbulence-driven heat transport with system size in magnetically confined plasmas is reexamined using first-principles based numerical simulations. Two very different numerical methods are applied to this problem, in order to resolve a long ...

The negative triangularity tokamak (NTT) is a unique reactor concept based on 'power-handling-first' philosophy with the heat exhaust problem as the leading concern. The present paper exposes a reactor concept using L-mode edge based on NTT configuration, ...

Frequency chirping of Alfven modes, a phenomenon observed in tokamak fusion plasmas driven by energetic particles (EPs), can result in significant losses of EPs. In this study, we use the global gyrokinetic code ORB5 (Lanti et al 2020 Comput. Phys. Commun. ...

Frequency locking of edge localized modes (ELMs) to the vertical plasma movements induced by magnetic perturbations first demonstrated in TCV was successfully repeated in ASDEX Upgrade. However, the ELMs were triggered in ASDEX Upgrade when the plasma was ...

A common feature of the Vlasov equation is that it develops fine-scale filamentation as time evolves, as observed, for example, in global nonlinear simulations of the ion-temperature-gradient instability. From a numerical point of view, it is not trivial t ...

This paper is a written summary of an overview oral presentation given at the 1st Spanish Fusion High Performance Computer (HPC) Workshop that took place on the 27 November 2020 as an online event. Given that over the next few years ITER24 will move to its ...

In this work, we use the global electromagnetic and electrostatic gyro kinetic approaches to investigate the effects of zonal flows forced-driven by Alfvén modes due to their excitation by energetic particles on the dynamics of ITG (ion temperature gradien ...

A simple configuration that consists of a set of toroidal, helical and vertical field coils is used to calculate free boundary equilibria with non-zero plasma current and approximately helically symmetric plasma boundary shape. The amount of helical boundary deformation is controlled by the ratio of the current in the helical field coils to the current in the toroidal field coils. When this ratio is increased, the (m, n) = (2, 1) external kink is stabilized at beta similar or equal to 1% for inverse rotatio

We introduce and derive the Fourier -enhanced 3D electrostatic field solver of the gyrokinetic full -f PIC code PICLS. The solver makes use of a Fourier representation in one periodic direction of the domain to make the solving of the system easily paralle ...

This paper presents the current state of the global gyrokinetic code Orb5 as an update of the previous reference (Jolliet et al., 2007). The Orb5 code solves the electromagnetic Vlasov–Maxwell system of equations using a PIC scheme and also includes collis ...

Over the past decades, multiple gyrokinetic codes have shown to be able to simulate turbulence and associated transport in the core of Tokamak devices. However, their application to the edge and scrape-off layer (SOL) region presents significant challenges ...

The gyrokinetic particle-in-cell code PICLS is a full-f finite element tool to simulate turbulence in open and closed field lines. During the previous year, the capability of PICLS was extended to encompass electromagnetic effects. Successful tests using t ...

Laurent Villard

Chat with Graph Search

Geometrical and Profile Effects on Toroidicity and Ellipticity Induced Alfven Eigenmodes

On the definition of a kinetic equilibrium in global gyrokinetic simulations

First principles gyrokinetic analysis of electromagnetic plasma instabilities

Global Alfven eigenmode stability in thermonuclear tokamak plasmas

Stability of Alfven eigenmodes in optimized tokamaks

Development of a Global Version of the Gyrokinetic Microturbulence Code GENE

Convolution and iterative methods applied to low frequency waves in 3D configurations

System size effects on gyrokinetic turbulence

L-mode-edge negative triangularity tokamak reactor

Nonlinear dynamics of nonadiabatic chirping-frequency Alfven modes in tokamak plasmas

Comparing magnetic triggering of ELMs in TCV and ASDEX Upgrade

Fine-scale structures and negative-density regions: Comparison of numerical methods for solving the advection equation

EUROfusion-theory and advanced simulation coordination (E-TASC): programme and the role of high performance computing

Ion temperature gradient mode mitigation by energetic particles, mediated by forced-driven zonal flows

Global ideal MHD stability of plasmas with toroidal, helical and vertical field coils

Verification of the Fourier-enhanced 3D finite element Poisson solver of the gyrokinetic full-f code PICLS

Orb5: A global electromagnetic gyrokinetic code using the PIC approach in toroidal geometry

Particle-in-cell methods in edge plasma physics: the PICLS code

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

Verification of the Picls Electromagnetic Upgrade in Mixed Variables