Publications de Laurent Villard

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The excitation of toroidicity-induced Alfven eigenmodes (TAEs) using prescribed external electromagnetic perturbations (hereafter 'antenna') acting on a confined toroidal plasma, as well as its nonlinear couplings to other modes in the system, is studied. ...

Abandoning the assumption of nested magnetic surfaces in tokamak plasma expands the field of research and opens up new approaches for both theoretical and experimental plasma physics. The computer code KINX for calculations of the ideal MHD stability was d ...

The work reported in this paper addresses two aspects. In the first part, numerical simulations are conducted to examine the impact of magnetic equilibrium shaping (elongation and triangularity), on both conventional Ion Temperature Gradient (ITG) modes an ...

In this work, we extend our previous studies (Singh et al 2023, Nucl. Fusion 63, 086029; Singh et al 2024, Nucl. Fusion 64, 106005) by performing global δf electromagnetic gyrokinetic simulations including collisions using the ORB5 particle-in-cell (PIC) code, spanning the plasma from magnetic axis to separatrix. The analysis focuses on ion temperature gradient (ITG) and trapped electron mode (TEM) turbulence in both linear and nonlinear regimes for experimentally relevant profiles and parameters of the ADI

In this work, linear and nonlinear collisionless electrostatic simulation studies of the standard and short wavelength ion temperature gradient mode (SWITG) for experimental profiles and parameters of ADITYA-U tokamak are performed using the linear global ...

Important steps towards the understanding of turbulent transport have been made with the development of the gyrokinetic framework for describing turbulence and with the emergence of numerical codes able to solve the set of gyrokinetic equations. This paper ...

Internal transport barriers (ITB) form through turbulence suppression, often observed when the safety factor profile exhibits an off-axis minimum. This work aims at improving our understanding of the conditions enabling the development of an ITB, using a m ...

Gyrokinetic simulations are extensively used as a tool to describe various phenomena in magnetically confined plasmas. Among others, turbulent transport induced by drift-wave type instabilities such as Ion Temperature Gradient (ITG), Trapped Electron Mode (TEM) and Electron Temperature Gradient (ETG) plays a central role in fusion research. While the ITG mode in first approximations can be modeled using a reduced adiabatic electron model, the TEM and ETG modes require a kinetic description. The global delta

The ubiquitous mode is investigated in the linear regime for the first time using a global gyrokinetic model. These modes are driven by the density gradient in trapped electron population but with mode frequency in the ion diamagnetic drift direction, in c ...

The implementation of linearized operators describing inter- and like-species collisions in the global gyrokinetic particle-in-cell code ORB5 [ S. Jolliet, Comput. Phys. Commun. 177, 409 (2007) ] is presented. A neoclassical axisymmetric equilibrium with s ...

This paper presents experimental results on the accessibility and the properties of plasmas with improved confinement in TCV. First, the H-mode threshold power is measured in Ohmic plasmas. Above an Ohmic threshold density, the threshold power increases with the density. A lower threshold density is found when additional electron cyclotron heating (ECH) is applied. At these low densities, the threshold power increases dramatically with decreasing density. Only a small fraction of the wide operational domain

A new diagnostic has been developed to investigate the wave-particle interaction in the phase-space in gyrokinetic particle-in-cell codes. Keeping information about energy transfer terms in the velocity space, the technique has been implemented and tested ...

Long global gyrokinetic turbulence simulations are particularly challenging in situations where the system deviates strongly from its initial state and when fluctuation levels are high, for example, in strong gradient regions. For particle-in-cell simulati ...

A global, gyro-kinetic nonlinear study of the ubiquitous mode (UM) for Lithium Tokamak eXperiment (LTX)-like profiles, under flat electron and ion temperature scenarios is conducted using a global gyrokinetic model. Exact MHD equilibria with circular shape ...

A global plasma turbulence simulation code, ORB5, is presented. It solves the gyrokinetic electrostatic equations including zonal flows in axisymmetric magnetic geometry. The present version of the code assumes a Boltzmann electron response on magnetic sur ...

The aim of this paper is to report on recent advances made in global gyrokinetic simulations of ion temperature gradient (ITG) modes and other microinstabilities. The nonlinear development and saturation of ITG modes and the role of E x B zonal flows are studied with a global nonlinear deltaf formulation that retains parallel nonlinearity and thus allows for a check of the energy conservation property as a means of verifying the quality of the numerical simulation. Due to an optimized loading technique, the

Two global gyrokinetic codes are benchmarked against each other by comparing simulation results in the case of ion temperature gradient driven turbulence, in the adiabatic electron response limit The two codes are the Eulerian code GENE and the Lagrangian ...

It is now widely believed that low frequency turbulence developing from smallscale instabilities is responsible for the phenomenon of anomalous transport generally observed in magnetic confinement fusion experiments. The microinstabilities are driven by gradients of equilibrium density, ion and electron temperatures and magnetic field strength. Gyrokinetic theory is based on the Vlasov-Maxwell equations and, consistent with the ordering, averages out the fast particle gyromotion, reducing the phase space fr

Turbulence and Transport Reduction with Negative Triangularity : Correlation ECE Measurements in TCV Due to turbulence, core energy transport in fusion devices such as tokamaks generally exceeds collisional transport by at least an order of magnitude. It is therefore crucial to understand the instabilities driving the turbulent state and to find ways to control them. Plasma shape is one of these fundamental tools. In low collisionality plasmas, such as in a reactor, changing the plasma shape from Dee-shape

A widespread method for gyrokinetic simulations relies on the discretization of distribution functions with numerical markers. The electromagnetic field is typically represented on a grid by finite differences or finite elements (Particle-In-Cell, PIC). When simulating large-sized systems, this method encounters performance losses, both locally (intra-CPU) and globally (inter-CPU) because the amount of communicated data increases. Another approach, Particle-In-Fourier (PIF), takes advantage of the anisotrop

Laurent Villard

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Linear and nonlinear excitation of TAE modes by external electromagnetic perturbations using ORB5

MHD Stability and Energy Principle for Two-Dimensional Equilibria without Assumption of Nested Magnetic Surfaces

Magnetic shaping effects on turbulence in ADITYA-U tokamak

Electromagnetic gyrokinetic simulation of drift wave turbulence in ADITYA-U with collisions

Gyrokinetic simulation of short wavelength ion temperature gradient instabilities in the ADITYA-U tokamak

Gyrokinetic simulations of turbulent transport: size scaling and chaotic behaviour

Global electromagnetic gyrokinetic simulations of internal transport barriers in reversed-shear tokamaks

An improved hybrid electron model for global gyrokinetic simulations using the ORB5 PIC code

Global gyrokinetic study of density gradient driven instability in tokamaks: the ubiquitous mode

Neoclassical equilibria as starting point for global gyrokinetic microturbulence simulations

Accessibility and properties of ELMy H-mode and ITB plasmas in TCV

Implementation of energy transfer technique in ORB5 to study collisionless wave-particle interactions in phase-space

Gyrokinetic simulations of turbulence and zonal flows driven by steep profile gradients using a delta-f approach with an evolving background Maxwellian

Gyrokinetic transport driven by ubiquitous modes in LTX-like tokamak with ‘flat’ temperature

A global collisionless PIC code in magnetic coordinates

Full radius linear and nonlinear gyrokinetic simulations for tokamaks and stellarators: zonal flows, applied E x B flows, trapped electrons and finite beta

Nonlinear quasisteady state benchmark of global gyrokinetic codes

First principles based simulations of instabilities and turbulence

Transport and turbulence reduction with negative triangularity : Correlation ECE measurements in TCV

The Particle-In-Fourier (PIF) Approach Applied to Gyrokinetic Simulations