Quantification of locked mode instability triggered by a change in confinement

Peterka, M.; Seidl, J.; Markovic, T.; Loarte, A.; Logan, N. C.; Park, J. -K.; Cahyna, P.; Havlicek, J.; Imrisek, M.; Kripner, L.; Panek, R.; Sos, M.; Bilkova, P.; Bogar, K.; Bohm, P.; Casolari, A.; Gribov, Y.; Grover, O.; Hacek, P.; Hron, M.; Kovarik, K.; Tomes, M.; Tskhakaya, D.; Varju, J.; Vondracek, P.; Weinzettl, V.

doi:10.1088/1741-4326/ad6ce7

Title: Quantification of locked mode instability triggered by a change in confinement

Journal Article · 03 September 2024 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/ad6ce7 · OSTI ID:2439350

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; Gribov, Y.;

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Abstract This work presents the first analysis of the disruptive locked mode (LM) triggered by the dynamics of a confinement change. It shows that, under certain conditions, the LM threshold during the transient is significantly lower than expected from steady states. We investigate the sensitivity to a controlled n = 1 error field (EF) activated prior to the L-H transition in the COMPASS tokamak, at q ₉₅ ∼ 3, β _N ∼ 1, and using EF coils on the high-field side of the vessel. A threshold for EF penetration subsequent to the L-H transition is identified, which shows no significant trend with density or applied torque, and is an apparent consequence of the reduced intrinsic rotation of the 2/1 mode during this transient phase. This finding challenges the assumption made in theoretical and empirical works that natural mode rotation can be predicted by global plasma parameters and urges against using any parametric EF penetration scaling derived from steady-state experiments to define the EF correction strategy in the entire discharge. Furthermore, even at EFs below the identified penetration threshold, disruptive locking of sawtooth-seeded 2/1 tearing modes is observed after about 30% of L-H transitions without external torque.

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Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: SC0021968

OSTI ID:: 2439350

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 10 Vol. 64; ISSN 0029-5515

Publisher:: IOP PublishingCopyright Statement

Country of Publication:: IAEA

Language:: English

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