State Reconstruction and Noise Reduction by Kalman Filter in the Vertical Position Control on Alcator C-Mod

The main sources of noise and pickups in Alcator C-Mod are identified, and their effects on the measurement and control of the vertical position are evaluated. Broadband noise may affect controllability of C-Mod plasmas at limit elongations and may become an issue with high-order controllers; therefore, two applications of Kalman filters are investigated. A Kalman filter is compared to a state observer based on the pseudoinverse of the measurement matrix and proves to be a better candidate for state reconstruction for vertical stabilization, provided adequate models of the system, the inputs, the process, and measurement noise and an adequate set of diagnostic measurements are available. A single-input single-output application of the filter for the vertical observer rejects high-frequency noise without destabilizing high-elongation plasmas.