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Feedback suppression of rotating external kink instabilities in the presence of noise
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View: Figures


Image of FIG. 1.
FIG. 1.

The arrangement of the conducting wall sections, radial control coils, and poloidal sensor coils on HBT-EP.

Image of FIG. 2.
FIG. 2.

Evolutions of the plasma current and edge safety factor for a typical discharge in the feedback experiments. The external kink mode appears when surface is near the edge of the plasma, in the range .

Image of FIG. 3.
FIG. 3.

Poloidal field fluctuations measured from the plasma surface for (a) no feedback, (b) positive feedback using the Kalman filter, and (c) negative feedback with the Kalman filter.

Image of FIG. 4.
FIG. 4.

Frequency spectrum of poloidal field fluctuations in arbitrary units as a function of the phase angle between feedback and the measured mode. Feedback may be phased to either suppress or excite the mode near , but the Kalman filter prevents excitation at higher frequencies.

Image of FIG. 5.
FIG. 5.

Adding flat-spectrum, Gaussian noise to the mode calculated by the FPGA algorithm showcases the Kalman filter’s noise removal capability. Plot (a) shows a simulation of the cosine mode as calculated in the DFT step in the algorithm (black) and the sum of this signal with the cosine component of the added noise (gray). Plots (b) and (c) show one of five FPGA outputs to the control coils in the added noise experiments for algorithms with and without the Kalman filter, phased to excite the mode.

Image of FIG. 6.
FIG. 6.

A comparison of the frequency spectrum of the poloidal field for added noise experiments, for feedback off (solid), Kalman filter mode ID feedback (dotted), and mode ID feedback (dashed) discharges. Plots (a) and (c) show suppression and excitation experiments with no added noise. Plots (b) and (d) show the suppression and excitation cases with extra noise added to the feedback algorithms. With the added noise, the algorithm without the Kalman filter loses its ability to suppress and excite the mode, while the Kalman filter algorithm does not.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Feedback suppression of rotating external kink instabilities in the presence of noise