Control of the resistive wall mode with internal coils in the DIII-D tokamak
Artikel i vetenskaplig tidskrift, 2005
Internal coils, 'I-Coils', were installed inside the vacuum vessel of the DIII-D device to generate non-axisymmetric magnetic fields to act directly on the plasma. These fields are predicted to stabilize the resistive wall mode (RWM) branch of the long-wavelength external kink mode with plasma beta close to the ideal wall limit. Feedback using these I-Coils was found to be more effective as compared to using external coils located outside the vacuum vessel. Locating the coils inside the vessel allows for a faster response and the coil geometry also allows for better coupling to the helical mode structure. Initial results were reported previously (Strait E.J. et al 2004 Phys. Plasmas 11 2505). This paper reports on results from extended feedback stabilization operations, achieving plasma parameters up to the regime of Cβ ≈ 1.0 and open loop growth rates of γopenτw ≳ 25 where the RWM was predicted to be unstable with only the 'rotational viscous stabilization mechanism'. Here Cβ ≈ (β - βno-wall.limit)/(βideal.wall.limit - βno-wall.limit) is a measure of the beta relative to the stability limits without a wall and with a perfectly conducting wall, and τw is the resistive flux penetration time of the wall. These feedback experimental results clarified the processes of dynamic error field correction and direct RWM stabilization, both of which took place simultaneously during RWM feedback stabilization operation. MARS-F modelling provides a critical rotation velocity in reasonable agreement with the experiment and predicts that the growth rate increases rapidly as rotation decreases below the critical. The MARS-F code also predicted that for successful RWM magnetic feedback, the characteristic time of the power supply should be limited to a fraction of the growth time of the targeted RWM. The possibility of further improvements in the presently achievable range of operation of feedback gain values is also discussed.
Författare
M. Okabayashi
General Atomics
Princeton University
J. Bialek
Columbia University
Anders Bondeson
Chalmers, Tillämpad mekanik
M. S. Chance
Princeton University
M. S. Chu
General Atomics
A. M. Garofalo
Columbia University
R. Hatcher
Princeton University
Y. In
FAR-TECH, Inc.
G. L. Jackson
General Atomics
R. J. Jayakumar
Lawrence Livermore National Laboratory
T. H. Jensen
General Atomics
O. Katsuro-Hopkins
Columbia University
R. J. La Haye
General Atomics
Yueqiang Liu
Chalmers
G. A. Navratil
Columbia University
H. Reimerdes
Columbia University
J. T. Scoville
General Atomics
E. J. Strait
General Atomics
M. Takechi
Japan Atomic Energy Agency
A. D. Turnbull
General Atomics
P. Gohil
General Atomics
J. S. Kim
Japan Atomic Energy Agency
M. A. Makowski
Lawrence Livermore National Laboratory
J. Manickam
Princeton University
J. Menard
Princeton University
Nuclear Fusion
0029-5515 (ISSN) 1741-4326 (eISSN)
Vol. 45 12 1715-1731Ämneskategorier
Maskinteknik
DOI
10.1088/0029-5515/45/12/028