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

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 RFX-mod experiments motivated similar ones in DIII-D L-mode diverted Tokamak plasmas at low q 95. 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,more » as simulations with the linear MHD code IPEC suggest. A significant rotation braking in the plasma core is also observed in DIII-D. Finally, numerical calculations of the neoclassical toroidal viscosity (NTV) carried out with PENT identify this torque as a possible contributor for this effect.« less
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [2] ;  [2] ;  [1] ;  [4] ;  [4] ;  [2] ;  [3] ;  [4] ;  [1] ;  [4]
  1. Consorzio RFX (CNR, ENEA, INFN, Univ. di Padova, Acciaierie Venete SpA), Padova (Italy)
  2. Columbia Univ., New York, NY (United States)
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  4. General Atomics, San Diego, CA (United States)
Publication Date:
Grant/Contract Number:
FG02-04ER54761; AC02-09CH11466; FC02-04ER54698; 633053
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 56; Journal Issue: 10; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; sawtooth instability; 3D magnetic fields; low-q plasmas
OSTI Identifier:
1335695
Alternate Identifier(s):
OSTI ID: 1373937