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Moyer, R. A.; Paz-Soldan, C.; Nazikian, R.; Orlov, D. M.; Ferraro, N. M.; Grierson, B. A.; Knölker, M.; Lyons, B. C.; McKee, G. R.; Osborne, T. H.; Rhodes, T. L.; Meneghini, O.; Smith, S.; Evans, T. E.; Fenstermacher, M. E.; Gröbner, R. J.; Hanson, J. M.; La Haye, R. J.; Luce, T. C.; Mordijck, S.; Solomon, W. M.; Turco, F.; Yan, Z.; Zeng, L. (2017): Validation of the model for ELM suppression with 3D magnetic fields using low torque ITER baseline scenario discharges in DIII-D. In: Physics of Plasmas, Vol. 24, No. 10, 102501
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Abstract

Experiments have been executed in the DIII-D tokamak to extend suppression of Edge Localized Modes (ELMs) with Resonant Magnetic Perturbations (RMPs) to ITER-relevant levels of beam torque. The results support the hypothesis for RMP ELM suppression based on transition from an ideal screened response to a tearing response at a resonant surface that prevents expansion of the pedestal to an unstable width [Snyder et al., Nucl. Fusion 51, 103016 (2011) and Wade et al., Nucl. Fusion 55, 023002 (2015)]. In ITER baseline plasmas with I/aB = 1.4 and pedestal nu* similar to 0.15, ELMs are readily suppressed with co-I-p neutral beam injection. However, reducing the beam torque from 5 Nm to <= 3.5 Nm results in loss of ELM suppression and a shift in the zero-crossing of the electron perpendicular rotation omega(perpendicular to e) similar to 0 deeper into the plasma. The change in radius of omega(perpendicular to e) similar to 0 is due primarily to changes to the electron diamagnetic rotation frequency omega(e)*. Linear plasma response modeling with the resistive MHD code M3D-c1 indicates that the tearing response location tracks the inward shift in omega(perpendicular to e) similar to 0. At pedestal nu* similar to 1, ELM suppression is also lost when the beam torque is reduced, but the omega(perpendicular to e) change is dominated by collapse of the toroidal rotation v(T). The hypothesis predicts that it should be possible to obtain ELM suppression at reduced beam torque by also reducing the height and width of the omega(e)* profile. This prediction has been confirmed experimentally with RMP ELM suppression at 0 Nm of beam torque and plasma normalized pressure beta(N) similar to 0.7. This opens the possibility of accessing ELM suppression in low torque ITER baseline plasmas by establishing suppression at low beta and then increasing beta while relying on the strong RMP-island coupling to maintain suppression. Published by AIP Publishing.