Modelling of macroscopic magnetic islands in tokamaks
F. Porcelli · A. Airoldi · C. Angioni · A. Bruschi · P. Buratti · F. Califano · S. Cirant · I. Furno · D. Grasso · E. Lazzaro · A. A. Martynov · M. Ottaviani · F. Pegoraro · G. Ramponi · E. Rossi · O. Sauter · C. Tebaldi · O. Tudisco
Abstract and summary · read the original at the source
In one page
A tokamak holds its plasma inside nested magnetic surfaces, like the layers of an onion. Sometimes a layer tears and reconnects into a magnetic island — a bubble of field lines that short-circuits the insulation and lets heat run out of the core. Porcelli and seventeen colleagues bring the experiment and the theory together for the two large versions of that behaviour: the sawtooth, in which the plasma centre repeatedly crashes and rebuilds, and the neoclassical tearing mode, an island that feeds on the plasma’s own pressure-driven current. They report a model that predicts how often a sawtooth crashes and how big the crash is, checked against measurements from the FTU and TCV tokamaks. They show that diamagnetic effects — the drift that comes with a pressure gradient — set both the threshold for a crash and the rate at which an island turns. And they clarify how reconnection proceeds when collisions are too rare to matter, where phase mixing rather than electrical resistance decides how far an island grows before it settles.
Why it matters hereChapter 9 is about plasma that organises itself into large, long-lived magnetic structures, and the tokamak island is the best-instrumented example anyone has: it forms on its own, it rotates, it saturates, and it can be steered with a microwave beam. Chapter 12 keeps the ledger of fusion routes, and controlling these islands is the difference between a machine that holds its plasma and one that loses it.
What it claims
01The subject is the dynamics of sawteeth and neoclassical tearing modes — the two large-scale magnetic reorganisations that decide what a tokamak can actually hold — treated together, with the experiment and the modelling set against each other rather than reported apart.Title and abstract, opening sentence
Published and peer-reviewed02A model that predicts the sawtooth period and the sawtooth amplitude is validated experimentally, on data from two different machines: the FTU tokamak and the TCV tokamak.Abstract, main finding (1)
Published and peer-reviewed03Diamagnetic effects — the drift that accompanies a pressure gradient — matter twice over: they help set the threshold at which a sawtooth crash is triggered, and they set the rotation of non-linear tearing modes.Abstract, main finding (2)
Published and peer-reviewed04Reconnection does not need collisions to proceed. In dissipationless regimes the growth and the saturation of a magnetic island are governed by phase mixing, and the paper sets out that collisionless mechanism explicitly.Abstract, main finding (3)
Published and peer-reviewed05Electron cyclotron resonance heating and macroscopic island dynamics act on each other, so a steerable microwave beam is a handle on the island rather than only a way of heating the plasma.Abstract, closing sentence
Published and peer-reviewed06What follows from all of this is whether a validated sawtooth model plus a microwave beam aimed at the island adds up to reliable control of macroscopic islands in a reactor-scale machine — the measurement that decides it is island suppression sustained on a burning plasma, not on the metre-scale devices this work draws on.Abstract, main finding (1) read with the closing sentence
What to watch
Read it · abstract
Abstract
The article presents experimental and theoretical investigations on the dynamics of sawteeth and neoclassical tearing modes in tokamak plasmas. The main findings of these investigations are: (1) The experimental validation, on the basis of FTU and TCV data, of a model for the prediction of the sawtooth period and amplitude; (2) the importance of diamagnetic effects in determining the threshold for sawtooth crashes and the rotation of non-linear tearing modes; (3) a clarification of collisionless reconnection processes, in particular the role of phase mixing in association with magnetic island growth and saturation in dissipationless regimes. The interplay between ECRH and macroscopic island dynamics is also discussed.
F. Porcelli, A. Airoldi, C. Angioni, A. Bruschi, P. Buratti, F. Califano, S. Cirant, I. Furno, D. Grasso, E. Lazzaro, A. A. Martynov, M. Ottaviani, F. Pegoraro, G. Ramponi, E. Rossi, O. Sauter, C. Tebaldi and O. Tudisco, Modelling of macroscopic magnetic islands in tokamaks, Nuclear Fusion 41, issue 9, 1207–1218 (2001). The experimental data come from the FTU and TCV tokamaks.
(Abstract only — see the rights note above. On this site, rotating nonlinear magnetic islands in a tokamak plasma are at /library/stm-c728aa7225, the effect of a shear flow profile on island stability is at /library/stm-95d2311119, disruption control with electron cyclotron heating on FTU and ASDEX Upgrade is at /library/stm-fcdb04e159, and flow generated by electrostatic turbulence in tokamaks is at /library/stm-ea244957db.)
The way in
https://doi.org/10.1088/0029-5515/41/9/309Published as Nuclear Fusion 41, issue 9, pages 1207 to 1218 (2001), copyright IOP Publishing, with no licence recorded in Crossref, so the sheet is abstract-only. No open full text was reachable on 2026-09-08: the IOP article page refuses automated requests, and although OpenAlex and Unpaywall both list EPFL Infoscience record 119803 as a green open-access location, the repository item there carries bibliographic metadata only — its sole content bundle is a licence file and no article file is attached. The abstract below therefore comes from the OpenAIRE record for this DOI, cross-checked word for word against the CoLab record for the same DOI, with the ligature losses of one deposited copy repaired against the other so that findings, effects and clarification read correctly. Every claim is located to the published abstract, which enumerates the work’s own main findings; note that the OpenAlex abstract field for this DOI is corrupt, carrying the title and author list in place of the abstract.
How to cite it
F. Porcelli, A. Airoldi, C. Angioni, A. Bruschi, P. Buratti, F. Califano, S. Cirant, I. Furno, D. Grasso, E. Lazzaro, A. A. Martynov, M. Ottaviani, F. Pegoraro, G. Ramponi, E. Rossi, O. Sauter, C. Tebaldi, O. Tudisco (2001) Modelling of macroscopic magnetic islands in tokamaks. doi:10.1088/0029-5515/41/9/309
Where it sits in the curriculum
Plasmoids, charge clusters and the orbsLattice confinement fusion