Control of sawteeth and triggering of NTMs with ion cyclotron resonance frequency waves in JET
A new scenario to delay or prevent neoclassical tearing mode (NTM) onset is presented. By active sawtooth destabilisation, short period and low amplitude sawteeth are generated, such that the sawtooth produced NTM seed island is reduced and the threshold normalised 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 stabilisation, 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 destabilised 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.
Bibliographic Reference: An article published in: Nuclear Fusion 42 (November 2002) 1324-1334
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://stacks.iop.org/0029-5515/42/1324
Record Number: 200215620 / Last updated on: 2002-12-02
Original language: en
Available languages: en