Comparison of RWM feedback systems with different input signals

The problem of better choice of the input signal for the resistive wall mode (RWM) feedback control is analysed. Three cases are compared: with radial field sensors, poloidal field sensors inside the vessel, and poloidal sensors outside. It is shown that, among the signals thus measured, the largest is the internal poloidal one. This makes the system with internal poloidal field sensors more attractive than the other two. The combination of poloidal and radial sensors is proposed as an even better choice. Several tests are proposed for experimental verification in DIII-D. (author)