Toroidal Modeling of RWM Feedback in the Presence of Control Voltage Saturation and Sensor Noise

Systematic, multiple initial value simulations are performed for a toroidal plasma using the recently updated MARS-F code in order to understand how the resistive wall mode (RWM) can be feedback controlled in the presence of control coil voltage saturation and/or sensor noise. The former renders the control nonlinear, thus generally requiring initial value computations for toroidal plasmas. This numerical study complements and confirms the key results from a previously analytic investigation of the RWM feedback with power saturation for a cylindrical plasma [Li et al., Physics of Plasmas, Vol. 19, 012502 (2012)]. Moreover, simulation results reveal a linear trend between the maximum tolerable sensor noise level and the degree of relaxing the control coil voltage saturation requirement, up to a certain level of noise, corresponding to a noise-to-signal ratio of about 25%. Beyond this level, further relaxing the control voltage saturation limit does not lead to increased sensor noise tolerance for the RWM stabilization.