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Control of sawteeth and triggering of NTMs with ion cyclotron resonance frequency waves in JET
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2002 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 42, no 11, 1324-1334 p.Article in journal (Refereed) Published
Abstract [en]

A new scenario to delay or prevent neoclassical tearing mode (NTM) onset is presented. By active sawtooth destabilization, short period and low amplitude sawteeth are generated, such that the sawtooth produced NTM seed island is reduced and the threshold normalized plasma pressure for triggering of NTMs, beta(Nonset), is increased. The scenario has been explored experimentally in the Joint European Torus (JET). Ion cyclotron resonance frequency (ICRF) waves tuned to the 2nd harmonic H-minority resonance have been used for sawtooth control. Whereas ICRF waves generally induce sawtooth stabilization, favouring the triggering of NTMs and reducing beta(Nonset), the present experiments show that by toroidally directed waves, ion cyclotron current drive is produced, and that sawteeth can be destabilized by careful positioning of the 2nd harmonic H resonance layer with respect to the sawtooth inversion radius. As a result, NTM onset is delayed and beta(Nonset) is increased above its value obtained in discharges with additional heating from neutral beam injection alone.

Place, publisher, year, edition, pages
2002. Vol. 42, no 11, 1324-1334 p.
Keyword [en]
neoclassical tearing modes, current drive, beta-limit, magnetic islands, asdex upgrade, stabilization, tokamak, perturbations, onset, discharges
URN: urn:nbn:se:kth:diva-22105DOI: 10.1088/0029-5515/42/11/306ISI: 000179669300008OAI: diva2:340803
QC 20100525Available from: 2010-08-10 Created: 2010-08-10Bibliographically approved

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Hellsten, Torbjörn A. K.Johnson, Thomas J.
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Alfvén Laboratory
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