Optimal Control of the Plasma Azimuthal Velocity Profile by Feedback ExB Actuation in HELCAT
Z.O. Ilhan, D. Huxley-Cohen, H. Wang, E. Schuster, M. Gilmore, and A. Ware
IEEE Transactions on Plasma Science, vol. 42, no. 3, pp. 469-476, March 2014
Abstract
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Active control of the flow shear, which is related to the radial derivative of the azimuthal flow, is a key
factor in reducing the cross-field turbulence-driven particle transport in a magnetically confined plasma column.
Once a desired radial azimuthal velocity profile and its associated level of turbulent fluctuations are identified,
the challenge of systematically achieving and sustaining it still remains. In this paper, a model-based feedback
controller is proposed to overcome this challenge in helicon-cathode (HELCAT). This linear, dual-source,
magnetized-plasma, laboratory device employs concentric ring electrodes to mitigate the turbulent plasma transport
by generating a sheared radial electric field and modifying the flow profiles by ExB actuation.
A linear-quadratic-integral optimal feedback controller is designed to minimize a weighted combination of the
tracking error and the control effort with an ultimate goal of regulating the radial azimuthal velocity profile
around a prescribed desired profile even with external disturbances and perturbed initial conditions. Numerical
simulations show the effectiveness of the proposed controller in shaping the azimuthal flow profile in HELCAT.
The proposed control solution has the potential of being used as a systematic tool for physics-oriented studies
in laboratory plasmas such as those achieved in HELCAT.