STM-D-1111Paper2009Published and peer-reviewed

Disruption control on FTU and ASDEX Upgrade with ECRH

B. Esposito · G. Granucci · S. Nowak · J. R. Martin-Solis · L. Gabellieri · E. Lazzaro · P. Smeulders · M. Maraschek · G. Pautasso · J. Stober · W. Treutterer · L. Urso · F. Volpe · H. Zohm · FTU, ECRH and ASDEX Upgrade Teams

Abstract and summary · read the original at the source · none found

In one page

A tokamak holds its plasma in a magnetic bottle, and a disruption is that bottle failing: the current collapses in milliseconds and dumps its energy into the wall. Esposito, Granucci, Nowak and colleagues, working on the FTU tokamak at Frascati and on ASDEX Upgrade at Garching, show that one can be headed off with a beam of microwaves. They trigger disruptions deliberately — firing molybdenum into the plasma with a laser, or pushing the density past the Greenwald limit with puffed deuterium — and watch the loop voltage for the rise that says one is coming. That signal fires electron-cyclotron heating aimed at a radius chosen before the shot. When the beam lands on one of the magnetic islands growing inside the plasma, that island stops growing, the modes coupled to it settle as well, and the current collapse is delayed or avoided outright, with the discharge recovering completely. Power matters: on ASDEX Upgrade 0.6 megawatts aimed near the resonant surface delays the dangerous mode, and 0.35 megawatts does not.

Why it matters hereChapter 9 follows plasma that organises itself into structures which persist and carry current, and here the structure is a magnetic island growing inside a tokamak — this is a demonstration that a well-aimed beam can address one directly and stop it. Chapter 12 needs the result because a machine that disrupts is a machine that cannot be relied on to make energy, and this paper writes the whole control loop out: precursor, trigger, aim, outcome.

What it claims

01Electron cyclotron resonance heating is a promising technique for avoiding or postponing disruptions, and it was tested in dedicated experiments on two machines, FTU and ASDEX Upgrade, with the disruptions produced deliberately — by injecting molybdenum through laser blow-off on FTU, or by puffing deuterium gas above the Greenwald density limit on both machines.Abstract, first three sentences
Published and peer-reviewed
02The control loop is explicit and repeatable. The toroidal magnetic field is held fixed, the launching mirrors are steered before every discharge so that the microwave power is deposited at a chosen radius, and the loop voltage signal serves as the disruption precursor that triggers the heating power before the plasma current quench.Abstract
Published and peer-reviewed
03On FTU, at plasma currents of 0.35 to 0.5 megaamperes, a toroidal field of 5.3 tesla and 0.4 to 1.2 megawatts of heating power, applying the beam modifies the time at which the current quench starts, and the modification depends on where the power is deposited.Abstract
Published and peer-reviewed
04The mechanism is island-level and specific. A scan in deposition location shows that directly heating one of the magnetic islands produced by resistive magnetohydrodynamic instabilities — with mode numbers m over n of 3 over 2, 2 over 1 or 3 over 1 — prevents that island from growing further, also stabilises the other coupled modes, and delays the current quench or avoids it entirely; disruption avoidance with complete recovery of the discharge is obtained when the power is applied on rational surfaces.Abstract
Published and peer-reviewed
05The modes involved in the disruption are identified as tearing modes stabilised by strong local heating, and their evolution is reproduced using the Rutherford equation, so the effect is not only observed but modelled with the standard island-growth theory.Abstract
Published and peer-reviewed
06There is a power threshold, and it is the number to watch. On ASDEX Upgrade, in L-mode plasmas at 0.6 megaamperes and 2.5 tesla, injecting 0.6 megawatts — comparable to the ohmic heating power — close to the q equals 2 surface significantly delays the onset of the 2 over 1 mode and prolongs the discharge, with the density continuing to rise throughout that phase; when the injected power is reduced to 0.35 megawatts, no delay in the onset of the mode is observed at all.Abstract, closing sentences
What to watch

Read it · abstract

Abstract

The use of ECRH has been investigated as a promising technique to avoid or postpone disruptions in dedicated experiments in FTU and ASDEX Upgrade. Disruptions have been produced by injecting Mo through laser blow-off (FTU) or by puffing deuterium gas above the Greenwald limit (FTU and ASDEX Upgrade). The toroidal magnetic field is kept fixed and the ECRH launching mirrors have been steered before every discharge in order to change the deposition radius. The loop voltage signal is used as disruption precursor to trigger the ECRH power before the plasma current quench. In the FTU experiments (Ip = 0.35–0.5 MA, Bt = 5.3 T, PECRH = 0.4–1.2 MW) it is found that the application of ECRH modifies the current quench starting time depending on the power deposition location. A scan in deposition location has shown that the direct heating of one of the magnetic islands produced by magnetohydrodynamic (MHD) resistive instabilities (either m/n = 3/2, 2/1 or 3/1) prevents its further growth and also produces the stabilization of the other coupled modes and the delay of the current quench or its full avoidance. Disruption avoidance and complete discharge recovery are obtained when the ECRH power is applied on rational surfaces. The modes involved in the disruption are found to be tearing modes stabilized by a strong local ECRH heating. The Rutherford equation has been used to reproduce the evolution of the MHD modes. In the ASDEX Upgrade experiments L-mode plasmas (Ip = 0.6 MA, Bt = 2.5 T, PECRH = 0.6 MW ∼ POHM) the injection of ECRH close to q = 2 significantly delays the 2/1 onset and prolongs the duration of the discharge: during this phase the density continues to increase. No delay in the onset of the 2/1 mode is observed when the injected power is reduced to 0.35 MW.

B. Esposito, G. Granucci, S. Nowak, J. R. Martin-Solis, L. Gabellieri, E. Lazzaro, P. Smeulders, M. Maraschek, G. Pautasso, J. Stober, W. Treutterer, L. Urso, F. Volpe, H. Zohm and the FTU, ECRH and ASDEX Upgrade Teams, Disruption control on FTU and ASDEX Upgrade with ECRH, Nuclear Fusion 49, 065014 (2009).

(Abstract only, and the full text was not reachable — see the rights note above. On this site, the theory of the macroscopic magnetic islands this experiment is aimed at is at /library/stm-1990916bc3, the nonlinear rotating-island analysis behind it at /library/stm-c728aa7225, and the turbulence-driven flows that shape the same plasmas at /library/stm-ea244957db.)

The way in

https://doi.org/10.1088/0029-5515/49/6/065014SOURCE NOT REACHED IN FULL. The article is held by IOP Publishing as Nuclear Fusion volume 49, issue 6, article 065014, and Crossref carries no licence statement for it. Unpaywall and OpenAlex label it bronze open access, but the only address either gives is the publisher’s own PDF at iopscience.iop.org, which returns the publisher’s bot page rather than the file; a bronze label is not a Creative Commons licence in any case. On 2026-09-08 the paper was hunted through Crossref, OpenAlex, Unpaywall, OpenAIRE, Semantic Scholar and INSPIRE-HEP, and through the two institutional repositories that hold records of it: the Max Planck Society’s PuRe at pure.mpg.de, whose REST record for the item carries the bibliographic metadata and affiliations but no abstract and no file, and the CNR repository IRIS at iris.cnr.it, whose record states in terms that no files are associated with it. No repository copy or author preprint exists. The summary and every claim below are therefore written from the authors’ own complete abstract together with the bibliographic record, and every locator says Abstract, because the abstract is what was read. AUTHORS. Initials are left unexpanded because no publisher record consulted gives the authors’ given names. The registry record carried three empty strings at the end of the author list; those are the three collaboration credits in the published byline, deposited to Crossref without names as FTU, ECRH and ASDEX Upgrade Teams, and they are restored here as a single collaboration entry. The named authors are from the EURATOM-ENEA association at Frascati, the EURATOM-ENEA association at the CNR Institute of Plasma Physics in Milan, the Universidad Carlos III de Madrid, and the Max-Planck-Institut für Plasmaphysik at Garching.

How to cite it

B. Esposito, G. Granucci, S. Nowak, J. R. Martin-Solis, L. Gabellieri, E. Lazzaro, P. Smeulders, M. Maraschek, G. Pautasso, J. Stober, W. Treutterer, L. Urso, F. Volpe, H. Zohm, FTU, ECRH and ASDEX Upgrade Teams (2009) Disruption control on FTU and ASDEX Upgrade with ECRH. doi:10.1088/0029-5515/49/6/065014

Where it sits in the curriculum

Plasmoids, charge clusters and the orbs Lattice confinement fusion