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Title: Stabilization of the vertical instability by non-axisymmetric coils

In a published Physical Review Letter [A. Reiman, Physical Review Letters, 99, 135007 (2007)], it was shown that axisymmetric (or vertical) stability can be improved by placing a set of parallelogram coils above and below the plasma oriented at an angle to the constant toroidal planes. The physics of this stabilization can be understood as providing an effective additional positive stability index. The original work was based on a simplified model of a straight tokamak and is not straightforwardly applicable to a finite aspect ratio, strongly shaped plasma such as in DIII-D. Numerical calculations were performed to provide a proof of principal that 3-D fields can, in fact raise the elongation limits as predicted, in a real DIII-D-like configuration. A four field period trapezoid-shaped coil set was developed in toroidal geometry and 3-D equilibria were computed using trapezium coil currents of ,10kA, 100kA, and 500kA. The ideal magnetohydrodynamics growth rates were computed as a function of the conformal wall position for the n=0 symmetry-preserving family. The results show an insignificant relative improvement in the stabilizing wall location for the two lower coil current cases, of the order of 10-3 and less. In contrast, the marginal wall position is increased bymore » 7% as the coil current is increased to 500kA, confirming the main prediction from the original study in a real geometry case. In DIII-D the shift in marginal wall position of 7% would correspond to being able to move the existing wall outward by 5 to 10 cm. While the predicted effect on the axisymmetric stability is real, it appears to require higher coil currents than could be provided in an upgrade to existing facilities. Lastly, additional optimization over the pitch of the coils, the number of field periods and the coil positions, as well as plasma parameters, such as the internal inductivity liβ, and q95 would mitigate this but seem unlikely to change the conclusion.« less
Authors:
 [1] ;  [2] ;  [1] ;  [3] ;  [1] ;  [1]
  1. General Atomics, San Diego, CA (United States)
  2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  3. Ecole Polytechnique Federale Lausanne (Switzlerland). Centre de Recherche en Physique des Plasma (CRPP)
Publication Date:
OSTI Identifier:
1371763
Grant/Contract Number:
FC02-04ER54698
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 56; Journal Issue: 8; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
General Atomics, San Diego, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Contributing Orgs:
Princeton Plasma Physics Laboratory, Princeton, New Jersey, USA Centre de Recherches en Physique des Plasmas, Lausanne, Switzerland
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; magnetohydrodynamic stability; axisymmetric stability; vertical stability; 3D magnetic fields