HBT-EP Active Mode Control Research*

The HBT-EP active MHD mode control program is studying advanced feedback control algorithms, ITER relevant internal feedback control coil configurations, and simultaneous control of internal and external MHD modes. The HBT-EP approach incorporates a segmented adjustable conducting wall, internal modular feedback control coils driven by a high-speed (10 microsec delay) MIMO digital control system for resistive wall modes (RWM), and edge rotation control using a biased electrode with supersonic nozzle fueling and lithium wall coating. Primary research thrusts are: (i) systematically study required feedback system gain as a function of control coil modularity and toroidal angle coverage compared with VALEN model predictions testing possible breakdown in basic ‘rigid mode’ model; (ii) test advanced feedback control techniques of adaptive filtering and equilibrium state estimation; (iii) study physics of RWM rotation stabilization by controlled variation of critical parameters (rotation, dissipation, and growth rate) using biased electrode ExB flow and control of ion charge exchange viscosity; (iv) use improved understanding and control capability to suppress tearing and kink type MHD modes simultaneously near the ideal wall limit.