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Active control for stabilization of neoclassical tearing modesa)
a)Paper LI1b 2, Bull. Am. Phys. Soc. 50, 220 (2005).
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View: Figures


Image of FIG. 1.
FIG. 1.

DIII-D ECCD system, including six gyrotrons, waveguide runs from gyrotrons to tokamak, and six independently steered launchers with mirror articulation for both poloidal and toroidal directions.

Image of FIG. 2.
FIG. 2.

Typical geometry for ECCD deposition in DIII-D plasmas. The EC power is absorbed at the second harmonic resonance location (vertical red line). Motional Stark effect diagnostic data is used with magnetic measurements in real-time equilibrium reconstruction to determine the location of the internal surfaces.

Image of FIG. 3.
FIG. 3.

(Color) (a) Saturated 3/2 NTM islands in DIII-D, illustrating typical relative dimensions of island and ECCD deposition region and (b) an expanded view of the deposition location.

Image of FIG. 4.
FIG. 4.

Summary of elements of the SEARCH AND SUPPRESS algorithm. This algorithm uses a systematic search of a chosen alignment parameter to find the optimal value of that parameter and stabilize the NTM.

Image of FIG. 5.
FIG. 5.

(Color) Probability potential function constructed by TARGET LOCK from time-series data (collected in real time during the sweep/jitter search process when the algorithm is used in a discharge, but here analyzing data from a SEARCH AND SUPPRESS case). Time increases into the paper. The potential function begins very broad and becomes narrower, localizing the optimal alignment location as time evolves in the discharge.

Image of FIG. 6.
FIG. 6.

Experimental application of TARGET LOCK algorithm to suppress 2/1 NTM.

Image of FIG. 7.
FIG. 7.

(Color) Example of SEARCH AND SUPPRESS followed by ACTIVE TRACKING to stabilize a 2/1 NTM using TF control and maintain suppression following disappearance of the island. denotes the major radius of the ECCD deposition spot, whereas denotes the major radius of the inboard resonant surface at the vertical position of the ECCD deposition.

Image of FIG. 8.
FIG. 8.

Illustration of refraction compensation predictor based on density and density profile peaking measurements.

Image of FIG. 9.
FIG. 9.

(Color) Schematic illustrating the integrated plasma control design process.

Image of FIG. 10.
FIG. 10.

(Color) Comparison of two simulations of NTM control action for two different choices of dwell time. A choice of dwell produces unsatisfactorily slow suppression, whereas a dwell time produces faster alignment and suppression.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Active control for stabilization of neoclassical tearing modesa)