Publications by Jonathan Graves

Schemes for Generating Deeply Trapped Fast Ions Via Ion-cyclotron-resonance Heating in Wendelstein 7-x

Wendelstein 7-X (W7-X) is a large, superconducting, optimized stellarator being operated in Greifswald, Germany. One of the original optimization criteria (Grieger et al 1992 Phys. Fluids B: Plasma Physics 4 2081) is good fast-ion confinement, mainly at in ...

IOP Publishing Ltd2025

Interplay of plasma resistivity and rotation on β limits in free boundary diverted tokamaks

Jonathan Graves

A plasma resistivity-β driving mechanism aimed at explaining the appearance of long wavelength global instabilities in free boundary high-β tokamak plasmas with a divertor is presented. These perturbations resemble very closely the resistive wall mode phen ...

2024

Direct prediction of saturated neoclassical tearing modes in slab using an equilibrium approach

Jonathan Graves, Joaquim Loizu Cisquella

We demonstrate for the first time that the nonlinear saturation of neoclassical tearing modes (NTMs) can be found directly using a variational principle based on Taylor relaxation, without needing to simulate the intermediate, resistivity-dependent dynamic ...

IOP Publishing2024

News and announcements from the Editor-in-Chief for 2024

Jonathan Graves

2024

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

Numerical tools for burning plasmas

Jonathan Graves, Laurent Villard, Emmanuel Lanti, Baruch Rofman, Alberto Bottino, Ben McMillan, Xiao Wang, Emanuele Poli

The software stack under development within a European coordinated effort on tools for burning plasma modelling is presented. The project is organised as a Task (TSVV Task 10) under the new E-TASC initiative (Litaudon et al 2022 Plasma Phys. Control. Fusio ...

IOP Publishing Ltd2023

Equilibrium β-limits dependence on bootstrap current in classical stellarators

Jonathan Graves, Joaquim Loizu Cisquella, Antoine Baillod

While it is important to design stellarators with high magnetohydrodynamic stability β-limit, it is also crucial to ensure that good magnetic surfaces exist in a large range of β values. As β increases, pressure-driven currents perturb the vacuum magnetic ...

Cambridge University Press2023

Exact expression for the hot plasma conductivity kernel in configuration space

Jonathan Graves, Mike Machielsen

Electromagnetic perturbations of a magnetized plasma cause induced charges and currents, collectively known as the plasma response. In the frequency domain, this response is a non-local functional of the electric field. The associated integral kernel, know ...

2023

Fast ion generation by combined RF-NBI heating in W7-X

Jonathan Graves, Mike Machielsen

Good fast ion confinement in quasi-isodynamic stellarators still has to be demonstrated experimentally. In the absence of fusion alphas, auxiliary heating systems can be used to generate fast ions. For this purpose, W7-X has neutral beam injection and its ...

Cambridge University Press2023

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

Laurent Villard, Jonathan Graves, Eric Serre

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 ...

2022