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Jonathan Graves

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Publications associées (326)

Sawtooth pacing by real-time auxiliary power control in a tokamak

Timothy Goodman, Olivier Sauter, Jonathan Graves, Federico Alberto Alfredo Felici

In the standard scenario of tokamak plasma operation, sawtooth crashes are the main perturbations that can trigger performance-degrading, and potentially disruption-generating, neoclassical tearing modes. This Letter demonstrates sawtooth pacing by real-ti ...

American Physical Society2011

Magentohydrodynamic Properties of Nominally Axisymmetric Systems with 3D Helical Core

Wilfred Anthony Cooper, Olivier Sauter, Jonathan Graves

Magnetohydrodynamic equilibrium states with a three-dimensional helical core are computed to model the MAST spherical tokamak and the RFX-mod reversed field pinch. The boundary is fixed as axisymmetric. The MAST equilibrium state has the appearance of an i ...

IOP Publishing2011

Magnetohydrodynamic properties of nominally axisymmetric systems with 3D helical core

Wilfred Anthony Cooper, Olivier Sauter, Jonathan Graves

2011

JET Snake Magnetohydrodynamic Equilibria

Wilfred Anthony Cooper, Olivier Sauter, Jonathan Graves

Magnetohydrodynamic (MHD) equilibrium states with a three-dimensional helical core that display the characteristics of a saturated ideal internal kink mode are computed to model snake structures that have been observed in the JET tokamak [A.~Weller et al. ...

IOP Publishing Ltd2011

Drift stabilization of ballooning modes in a high-$\langle \beta \rangle$ LHD configuration

Wilfred Anthony Cooper, Jonathan Graves, Lucie Brocher

Ideal MHD yields at best inconclusive predictions about the stability of the LHD heliotron for

\langle \beta \rangle \geq 3\%

. We investigate the impact of the drift stabilization of ballooning modes for the inward shifted LHD configuration (vacuum magne ...

IOP Publishing Ltd2010

Drift stabilization of ballooning modes in an inward-Shifted LHD configuration

Wilfred Anthony Cooper, Jonathan Graves, Lucie Brocher

A drift-magnetohydrodynamic theory is applied to a background anisotropic pressure equilibrium state to generate a drift corrected ballooning mode equation. The ratio of the mode frequency to the hot particle drift frequency constitutes the critical expans ...

Wiley-VCH2010

Neoclassical equilibria as starting point for global gyrokinetic microturbulence simulations

Stephan Brunner, Trach-Minh Tran, Laurent Villard, Alberto Bottino, Sébastien Jolliet, Jonathan Graves, Thibaut Vernay, Ben McMillan

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 ...

American Institute of Physics2010

The Effect of Plasma Profile Variation on the Stability of the n = 1 Internal Kink Mode in Rotating Tokamak Plasmas

Jonathan Graves

The sensitivity of the stability of the ideal n = 1 internal kink mode to variations in the plasma profiles is analysed both analytically and numerically in rotating tokamak plasmas. These stability analyses have been carried out including the centrifugal ...

IOP Publishing Ltd2010

Saturated ideal modes in advanced tokamak regimes in MAST

Jonathan Graves

MAST plasmas with a safety factor above unity and a profile with either weakly reversed shear or broad low-shear regions, regularly exhibit long-lived saturated ideal magnetohydrodynamic (MHD) instabilities. The toroidal rotation is flattened in the presen ...

IOP Publishing Ltd2010

Experimental verification of sawtooth control by energetic particles in ion cyclotron resonance heated JET tokamak plasmas

Stefano Coda, Jonathan Graves

Experimental evidence from the JET tokamak is presented supporting the predictions of a recent theory (Graves et al 2009 Phys. Rev. Lett. 102 065005) on sawtooth instability control by toroidally propagating ion cyclotron resonance waves. Novel experimenta ...

IOP Publishing Ltd2010

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

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

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

Empirical scaling of sawtooth period for onset of neoclassical tearing modes

Olivier Sauter, Stefano Coda, Jonathan Graves

Experimental observations from a range of tokamaks show that neoclassical tearing modes (NTMs) are triggered at lower plasma pressure when the sawtooth period is longer. A multi-machine database from nine tokamaks has been established in order to extrapola ...

IOP Publishing Ltd2010

Magnetic Reconnection Triggering Magnetohydrodynamic Instabilities during a Sawtooth Crash in a Tokamak Plasma

Wilfred Anthony Cooper, Jonathan Graves

Thomson scattering measurements with subcentimeter spatial resolution have been made during a sawtooth crash in a Mega Ampere Spherical Tokamak fusion plasma. The unparalleled resolution of the temperature profile has shed new light on the mechanisms that ...

APS2010

A new sawtooth control mechanism relying on toroidally propagating ion cyclotron resonance frequency waves: Theory and Joint European Torus tokamak experimental evidence

Stefano Coda, Jonathan Graves

The sawtooth control mechanism in plasmas employing toroidally propagating ion cyclotron resonance waves is extended. The asymmetrically distributed energetic passing ions are shown to modify the ideal internal kink mode when the position of the minority i ...

APS2010

Three-dimensional anisotropic pressure free boundary equilibria

Wilfred Anthony Cooper, Jonathan Graves

Free boundary three-dimensional anisotropic pressure magnetohydrodynamic equilibria with nested magnetic flux surfaces are computed through the minimisation of the plasma energy functional

W={\int}_{V}{d^3}x\left[{B^2}/(2\mu_0)+p_{||}/(\Gamma-1)\right]

. ...

2009

Importance of centrifugal effects for the internal kink mode stability in toroidally rotating tokamak plasmas

Jonathan Graves

Analytical theory and two different magnetohydrodynamical stability codes are used in a study of the effects of toroidal plasma rotation on the stability of the ideal, internal kink mode in tokamaks. The focus of the paper is on the role that the centrifug ...

American Institute of Physics (AIP)2009

BECOOL: Ballooning eigensolver with COOL finite elements

Wilfred Anthony Cooper, Jonathan Graves

An incompressible variational ideal ballooning mode equation is discretized with the COOL finite element discretization scheme using basis functions composed of variable order Legendre polynomials. This reduces the second order ordinary differential equati ...

2009

Sawtooth-Control Mechanism using Toroidally Propagating Ion-Cyclotron-ResonanceWaves in Tokamaks

Stefano Coda, Jonathan Graves

The sawtooth control mechanism in plasmas employing off-axis toroidally propagating ion cyclotron resonance waves in tokamaks is reinvestigated. The radial drift excursion of energetic passing ions distributed asymmetrically in the velocity parallel to the ...

American Physical Society2009

The effect of plasma triangularity on turbulent transport:modelling TCV experiments by linear and non linear gyrokinetic simulations

Stephan Brunner, Antoine Pochelon, Olivier Sauter, Laurent Villard, Stefano Coda, Yann Camenen, Jonathan Graves, Alessandro Marinoni, Xavier Lapillonne

The effect of plasma shape on confinement has been experimentally explored in the TCV tokamak revealing that the core electron heat transport is significantly reduced by a negative triangularity configuration, which could indicate a (partial) stabilization ...

2009

Anomalous transport of energetic particles in ITER relevant scenarios

Ambrogio Fasoli, Jonathan Graves, Mattia Albergante

Definitive simulations ...

American Institute of Physics (AIP)2009

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