Interaction of external n = 1 magnetic fields with the sawtooth instability in low-q RFX-mod and DIII-D tokamaks

Piron, C.; Martin, P.; Bonfiglio, D.; Hanson, J.; Logan, N. C.; Paz-Soldan, C.; Piovesan, P.; Turco, F.; Bialek, J.; Franz, P.; Jackson, G.; Lanctot, M. J.; Navratil, G. A.; Okabayashi, M.; Strait, E.; Terranova, D.; Turnbull, A.

doi:10.1088/0029-5515/56/10/106012

Title: Interaction of external n = 1 magnetic fields with the sawtooth instability in low-q RFX-mod and DIII-D tokamaks

Journal Article · Thu Aug 11 00:00:00 EDT 2016 · Nuclear Fusion

DOI:https://doi.org/10.1088/0029-5515/56/10/106012· OSTI ID:1335695

Piron, C. ^[1]; Martin, P. ^[1]; Bonfiglio, D. ^[1]; Hanson, J. ^[2]; Logan, N. C. ^[3]; Paz-Soldan, C. ^[4]; Piovesan, P. ^[1]; Turco, F. ^[2]; Bialek, J. ^[2]; Franz, P. ^[1]; Jackson, G. ^[4]; Lanctot, M. J. ^[4]; Navratil, G. A. ^[2]; Okabayashi, M. ^[3]; Strait, E. ^[4]; Terranova, D. ^[1]; Turnbull, A. ^[4]

Consorzio RFX (CNR, ENEA, INFN, Univ. di Padova, Acciaierie Venete SpA), Padova (Italy)
Columbia Univ., New York, NY (United States)
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
General Atomics, San Diego, CA (United States)

External n = 1 magnetic fields are applied in RFX-mod and DIII-D low safety factor Tokamak plasmas to investigate their interaction with the internal MHD dynamics and in particular with the sawtooth instability. In these experiments the applied magnetic fields cause a reduction of both the sawtooth amplitude and period, leading to an overall stabilizing effect on the oscillations. In RFX-mod sawteeth eventually disappear and are replaced by a stationary m = 1, n = 1 helical equilibrium without an increase in disruptivity. However toroidal rotation is significantly reduced in these plasmas, thus it is likely that the sawtooth mitigation in these experiments is due to the combination of the helically deformed core and the reduced rotation. The former effect is qualitatively well reproduced by nonlinear MHD simulations performed with the PIXIE3D code. The results obtained in these RFXmod experiments motivated similar ones in DIII-D L-mode diverted Tokamak plasmas at low q₉₅. These experiments succeeded in reproducing the sawtooth mitigation with the approach developed in RFX-mod. In DIII-D this effect is correlated with a clear increase of the n = 1 plasma response, that indicates an enhancement of the coupling to the marginally stable n = 1 external kink, as simulations with the linear MHD code IPEC suggest. A significant rotation braking in the plasma core is also observed in DIII-D. Numerical calculations of the Neoclassical Toroidal Viscosity (NTV) carried out with PENT identify this torque as a possible contributor for this effect.

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Research Organization:: Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States)

Sponsoring Organization:: USDOE

Grant/Contract Number:: FG02-04ER54761; AC02-09CH11466; FC02-04ER54698; 633053

OSTI ID:: 1335695

Alternate ID(s):: OSTI ID: 1373937

Journal Information:: Nuclear Fusion, Vol. 56, Issue 10; ISSN 0029-5515

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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Cited by: 9 works

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Mitigation of sawtooth crash as a manifestation of MHD mode coupling prior to disruption of KSTAR plasma Kim, Gnan; Yun, Gunsu S.; Woo, Minho Plasma Physics and Controlled Fusion, Vol. 61, Issue 5 https://doi.org/10.1088/1361-6587/aafe50	journal	March 2019

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