Scaling of the MHD perturbation amplitude required to trigger a disruption and predictions for ITER

0460364 - ÚFP 2017 RIV AT eng J - Journal Article
de Vries, P.C. - Pautasso, G. - Nardon, E. - Cahyna, Pavel - Gerasimov, S. - Havlíček, Josef - Hender, T.C. - Huijsmans, G.T.A. - Lehnen, M. - Maraschek, M. - Markovič, Tomáš - Snipes, J.A.
Scaling of the MHD perturbation amplitude required to trigger a disruption and predictions for ITER.
Nuclear Fusion. Roč. 56, č. 2 (2016), č. článku 026007. ISSN 0029-5515. E-ISSN 1741-4326
R&D Projects: GA MŠMT(CZ) LM2011021
EU Projects: European Commission(XE) 633053 - EUROfusion
Institutional support: RVO:61389021
Keywords : disruptions * locked modes * MHD instabilities * ITER * COMPASS tokamak
OECD category: Fluids and plasma physics (including surface physics)
Impact factor: 3.307, year: 2016
http://iopscience.iop.org/article/10.1088/0029-5515/56/2/026007/meta

The amplitude of locked instabilities, likely magnetic islands, seen as precursors to disruptions has been studied using data from the JET, ASDEX Upgrade and COMPASS tokamaks. It was found that the thermal quench, that often initiates the disruption, is triggered when the amplitude has reached a distinct level. This information can be used to determine thresholds for simple disruption prediction schemes. The measured amplitude in part depends on the distance of the perturbation to the measurement coils. Hence the threshold for the measured amplitude depends on the mode location (i.e. the rational q-surface) and thus indirectly on parameters such as the edge safety factor, q(95), and the internal inductance, li(3), that determine the shape of the q-profile. These dependencies can be used to set the disruption thresholds more precisely. For the ITER baseline scenario, with typically q(95) = 3.2, li(3) = 0.9 and taking into account the position of the measurement coils on ITER, the maximum allowable measured locked mode amplitude normalized to engineering parameters was estimated to be a.B-ML(r(c))/I-p = 0.92 m mT/MA, or directly as a fraction edge poloidal magnetic field: BML(r(c))/B theta(a) = 5 . 10(-3). But these values decrease for operation at higher q(95) or lower li(3). The analysis found furthermore that the above empirical criterion to trigger a thermal quench is more consistent with a criterion derived with the concept of a critical island size, i.e. the thermal quench seemed to be triggered at a distinct island width.
Permanent Link: http://hdl.handle.net/11104/0260461