Analysis of Feedback Experiments for the Control of Rotating Resistive Modes in HBT-EP

Investigation of the effect of a combination of close-fitting, adjustable conducting shell and magnetic feedback on MHD instabilities has been carried out in the HBT-EP tokamak. Simulation of the response of the feedback coils for the control of rotating resistive modes has been done by solving the dynamical equations^1 describing the nonlinear evolution of the tearing mode island width and frequency of rotation in 1D. A high-power amplifier is used to power a set of five discrete saddle coils to produce the external n=1, m=2 helical field. The amplitude and phase of the n=1, m=2 fluctuations are measured using a set of m=2 Fourier analyzing Rogowski coils. The results from the simulation are compared with those from the experiment. Supported by U. S. DOE Grant No. DE-FG02-86ER53222 ^1 E. Lazzaro and M. F. F. Nave, Phys. Fluids 31,1623 (1988)