Extending the RWM stability region by optimal feedback control

The stabilization of the resistive wall mode (RWM) instability in the DIII-D tokamak is necessary to maintain conditions for the plasma experiment. Stability has been achieved in experiments using proportional/derivative (PD) gain controllers. However, the stability range in terms of the mode growth rate ¿ is limited. Employing an optimal feedback controller in conjunction with a state estimator designed to reject sensor colored noise, the stability region of the system is greatly extended. Using experimental results, the power spectral density of the measurement noise is used to model the colored noise as a noise transfer function with a white noise input. The Linear Quadratic Gaussian (LQG) control technique is applied and results are compared to a traditional PD controller through simulations.