Optimal Closed-Loop Control of the Azimuthal Velocity Profile by ExB Actuation in HELCAT
Z. Ilhan, D. Huxley-Cohen, H. Wang, E. Schuster, M. Gilmore, A. Ware
Symposium on Fusion Engineering
San Francisco, California, USA, June 10-14, 2013
Abstract
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The cross-field turbulence-driven particle transport in magnetically
confined plasmas can be reduced by adequately shaping the flow profiles.
HELCAT (HELicon-CAThode), a linear magnetized plasma device, uses
concentric ring electrodes to modify the flow profiles by E×B actuation.
As a result, turbulent particle and heat transport can be mitigated by
generating a sheared radial electric field through the varying ring
voltages. Active control of the turbulent fluctu- ations, including the
associated cross-field particle transport, via manipulation of flow
profiles is investigated in this work. 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. A model-based feedback controller is proposed to
achieve this goal even in the presence of external disturbances, model
uncertainties and perturbed initial conditions. A
linear-quadratic-integral (LQI) optimal controller is designed to
minimize a weighted combination of the tracking error and the control
effort. Numerical simulations show the effectiveness of the proposed
controller to regulate the radial azimuthal velocity profile around a
prescribed desired profile. The proposed control solution has the
potential of being used as a systematic tool to elucidate the physics
of laboratory plasmas such as those achieved in HELCAT.