Publications associées à Magnetic helicity

Shedding light on the MRI-driven dynamo in a stratified shearing box

We study the magneto-rotational instability (MRI) dynamo in a geometrically thin disc (H/R < 1) using stratified zero net (vertical) flux shearing box simulations. We find that mean fields and electromotive forces (EMFs) oscillate with a primary frequency ...

2024

Dissipative magnetic structures and scales in small-scale dynamos

Jennifer Waltraud Schober

Small-scale dynamos play important roles in modern astrophysics, especially on galactic and extragalactic scales. Owing to dynamo action, purely hydrodynamic Kolmogorov turbulence hardly exists and is often replaced by hydromagnetic turbulence. Understandi ...

OXFORD UNIV PRESS2023

Occam's razor on the mechanism of resistive-wall-mode-induced beta limits in diverted tokamaks

Jonathan Graves, Daniele Brunetti

External kink modes, believed to be the drive of the 0-limiting resistive wall mode, are strongly stabilized by the presence of a separatrix. We thus propose a novel mechanism explaining the appearance of long-wavelength global instabilities in free bounda ...

2023

Dynamo instabilities in plasmas with inhomogeneous chiral chemical potential

Jennifer Waltraud Schober

We study the dynamics of magnetic fields in chiral magnetohydrodynamics, which takes into account the effects of an additional electric current related to the chiral magnetic effect in high-energy plasmas. We perform direct numerical simulations, consideri ...

American Physical Society2022

Modeling of saturated external MHD instabilities in tokamaks: A comparison of 3D free boundary equilibria and nonlinear stability calculations

Jonathan Graves

3D free boundary equilibrium computations have recently been used to model external kinks and edge harmonic oscillations (EHOs), comparing with linear MHD stability codes, and nonlinear analytic theory [Kleiner et al., Phys. Plasma Controlled Fusion 61, 08 ...

2022

A non-twisting flux tube for local gyrokinetic simulations

Stephan Brunner, Justin Richard Ball

Local gyrokinetic simulations use a field-aligned domain that twists due to the magnetic shear of the background magnetic equilibrium. However, if the magnetic shear is strong and/or the domain is long, the twist can become so extreme that it fails to prop ...

2021

Model for current drive induced crash cycles in W7-X

Joaquim Loizu Cisquella, Ajay Kumar

In the Wendelstein 7-X (W7-X) stellarator, the vacuum rotational transform, ι, has a flat radial profile and does not cross any major rational resonance. Nevertheless, during plasma operation the ι‐profile can be strongly modified by electron cyclotron cur ...

IOP Publishing Ltd2021

Development of free-boundary equilibrium and transport solvers for simulation and real-time interpretation of tokamak experiments

Francesco Carpanese

To exploit fusion as a source of energy, a hot and dense confined plasma is needed. This is achieved in tokamaks by actively controlling the plasma state meaning shape, position and internal kinetic profiles. This thesis addresses two topics: the developme ...

EPFL2021

Chiral fermion asymmetry in high-energy plasma simulations

Jennifer Waltraud Schober

The chiral magnetic effect (CME) is a quantum relativistic effect that describes the appearance of an additional electric current along a magnetic field. It is caused by an asymmetry between the number densities of left- and right-handed fermions, which ca ...

2020

Properties of a new quasi-axisymmetric configuration

Joaquim Loizu Cisquella

A novel, compact, quasi-axisymmetric configuration is presented which exhibits low fast-particle losses and is stable to ideal magnetohydrodynamic (MHD) instabilities. The design has fast-particle loss rates below 8% for flux surfaces within the half-radiu ...

IOP Publishing Ltd2019

Helical equilibrium magnetohydrodynamic flow effects on the stability properties of low-n ideal external-infernal modes in weak shear tokamak configurations

Wilfred Anthony Cooper, Jonathan Graves, Patrycja Nowak-Sliwinska, Daniele Brunetti, Alberto Mariani

The impact of equilibrium helical flows on the stability properties of low shear tokamak plasmas is assessed. The corrections due to such helical flow to the equilibrium profiles (mass density, pressure, Shafranov shift, magnetic fluxes) are computed by mi ...

IOP PUBLISHING LTD2019

Singular global components and frequency shift of the geodesic acoustic continuum modes in shaped tokamaks

Jonathan Graves

Within the ideal magnetohydrodynamic (MHD) model, the geodesic acoustic modes (GAMs) in tokamaks derived by Winsor et al (1968 Phys. Fluids 11 2448) belong to the continuous spectrum, characterised by unbounded non-square integrable eigenfunctions (delta f ...

2019

Magnetohydrodynamic theory of the global structure and magnetic components of geodesic acoustic modes in tokamaks

Jonathan Graves

Ideal magnetohydrodynamic (MHD) theory is used to investigate some of the fundamental properties of the geodesic acoustic continuum modes (GAMs) in tokamaks, including their global structure, their associated magnetic components both inside and outside the ...

IOP2016

Magnetohydrodynamics of chiral relativistic fluids

Alexey Boyarsky, Oleg Ruchayskiy

We study the dynamics of a plasma of charged relativistic fermions at very high temperature T >> m, where m is the fermion mass, coupled to the electromagnetic field. In particular, we derive a magnetohydrodynamical description of the evolution of such a p ...

American Physical Society2015

Magnetohydrodynamic helical structures in nominally axisymmetric low-shear tokamak plasmas

Olivier Sauter, Jonathan Graves, Wilfred Anthony Cooper, Holger Reimerdes, Antoine Pochelon, Federico David Halpern, Daniele Brunetti

The primary goal of hybrid scenarios in tokamaks is to enable high performance operation with large plasma currents whilst avoiding MHD instabilities. However, if a local minimum in the safety factor is allowed to approach unity, the energy required to ove ...

Iop Publishing Ltd2013

Exploitation of a general-coordinate guiding centre code for the redistribution of fast ions in deformed hybrid tokamak equilibria

Jonathan Graves, Wilfred Anthony Cooper, David Pfefferlé

Self-consistent fast ion distributions are usually obtained using a code that solves the guiding-centre equations, with an appropriate fast ion source (e.g. NBI pinis) and sink (e.g. collision operators). Straight field-line coordinate systems, such as Boo ...

Iop Publishing Ltd2012

Imaging of turbulent structures and tomographic reconstruction of TORPEX plasma emissivity

Ambrogio Fasoli, Ivo Furno, Christian Gabriel Theiler, Davoud Iraji

In the TORPEX [ A. Fasoli et al., Phys. Plasmas 13, 055902 (2006) ], a simple magnetized plasma device, low frequency electrostatic fluctuations associated with interchange waves, are routinely measured by means of extensive sets of Langmuir probes. To com ...

American Institute of Physics2010

Tokamak Magnetohydrodynamic Equilibrium States with Axisymmetric Boundary and a 3D Helical Core

Olivier Sauter, Laurent Villard, Jonathan Graves, Wilfred Anthony Cooper, Antoine Pochelon

Magnetohydrodynamic (MHD) equilibrium states with imposed axisymmetric boundary are computed in which a spontaneous bifurcation develops to produce an internal three-dimensional (3D) configuration with a helical structure in addition to the standard axisym ...

American Physical Society2010

Three-dimensional fluid simulations of a simple magnetized plasma

Paolo Ricci

Three-dimensional fluid simulations are performed in a simple magnetized toroidal plasma, in which vertical and toroidal magnetic fields create helicoidal magnetic field lines that terminate on the torus vessel. The simulations are carried out in the three ...

American Institute of Physics (AIP)2009

Gyrokinetic particle-in-cell global simulations of ion-temperature-gradient and collisionless-trapped-electron-mode turbulence in tokamaks

Sébastien Jolliet

The goal of thermonuclear fusion research is to provide power plants, that will be able to produce one gigawatt of electricity. Among the different ways to achieve fusion, the tokamak, based on magnetic confinement, is the most promising one. A gas is heat ...

EPFL2009