Feedback control of tokamak instabilities

The authors have made extensions and adaptation of theories of modern control science for lumped parameter systems (ODE) to disturbed parameter systems (PDE), like plasmas. Experimentally, they have performed several successful experiments in feedback stabilization of rvec E x rvec B rotationally driven mode and an ITG instability. They now propose generalization of the feedback theories so that they are applicable to multimode instabilities in tokamaks. They also propose unique suppressor structures suitable for tokamak applications. Specifically, they propose a modulated neutral beam suppressor for the control of major disruptions via feedback suppression of tearing and/or kink modes. The suppressor action is modeled by the beam momentum, particle and energy input in the respective conservation equations. They also propose a scheme for the control of the thermonuclear thermal instability via feedback modulated biasing of a poloidal divertor suppressor. The modulated biasing will result in an electric current and an associated heat flux along the magnetic field in the scrape-off layer. With an appropriate phase and amplitude this in turn will enhance the radial power loss to reduce the core temperature excursion and stabilize the instability. The necessary feedback power levels for ITER-like parameters will be estimated in both cases