PONDEROMOTIVE FEEDBACK STABILIZATION FOR CONTROL OF EXTERNAL KINK MODES AND DISRUPTIONS IN TOKAMAKS

A NOVEL APPROACH TO FEEDBACK CONTROL OF EXTERNAL KINK INSTABILITIES AND PLASMA DISRUPTIONS IN TOKAMAK MAGNETIC FUSION EXPERIMENTS WILL BE INVESTIGATED AND THE TECHNICAL REQUIREMENTS FOR A FEEDBACK STABILIZATION SYSTEM RELEVANT TO THE PRINCETON BETA EXPERIMENT (PBX-M) ESTIMATED. THE WORK IS BASED ON THE CONCEPT OF PONDEROMOTIVE STABILIZATION OF GLOBAL MAGNETOHYDRODYNAMIC (MHD) INSTABILITIES, WHICH HAS PREVIOUSLY BEEN STUDIED THEORETICALLY AND DEMONSTRATED IN MAGNETIC MIRRO EXPERIMENTS. CALCULATIONS SHOW THAT THE PONDEROMOTIVE FORCE PRODUCED BY SEVERAL ION BERNSTEIN WAVE (IBW) ANTENNAS CAN STABILIZE EXTERNAL KINK MODES IN ADVANCED TOKAMAK REGIMES (E.G., HIGH BETA POLOIDAL), BUT THE REQUIRED RADIO FREQUENCY (RF) POWER IS SEVERE WITHOUT FEEDBACK. IT IS PLANNED TO INVESTIGATE A FEEDBACK DISRUPTION CONTROL SYSTEM IN WHICH THE RF ANTENNAS WOULD BE MODULATED IN RESPONSE TO THE AMPLITUDE AND PHASE OF THE UNSTABLE KINK MODE, THEREBY REDUCING RF POWER REQUIREMENTS FOR STABILIZATION BY TWO ORDERS OF MAGNITUDE ACCORDING TO PRELIMINARY ESTIMATES. IN PHASE I, THE THEORY OF PONDEROMOTIVE STABILIZATION WILL BE REFORMULATED TO INCORPORATE A SIMPLE FEEDBACK MODEL, AND PRELIMINARY BENCHMARKING CALCULATIOONS FOR REALISTIC PBX-M EQUILIBRIA WILL BE CARRIED OUT USING THE PRINCETON MHD CODES. IF FEASIBILITY IS ESTABLISHED, A PHASE II FEEDBACK SYSTEM DEVELOPMENT EFFORT AND STABILIZATION EXPERIMENT WILL BE PLANNED TO TEST THE CONCEPT EXPERIMENTALLY ON PBX-M.