MHD Mode Studies during Wall Stabilization and Applied Resonant Magnetic Field Experiments(^*)

A diagnostic system measuring the soft X-ray emissivity distribution in HBT-EP plasmas has been built to study the changes of MHD mode structures during wall stabilization and the application of resonant magnetic fields. The system employs 32 observation channels which are located at one toroidal position and distributed uniformly around the plasma cross section. Several algorithms are used to reconstruct and simulate the emissivity distribution. The fluctuating part of the soft X-ray emissivity distribution provides a way of identifying the MHD modes. The influence of movable segmented shell on the MHD instability mode structure has been studied. Reconstruction and simulation have also been carried out to find the locations and sizes of islands produced with applied resonant magnetic fields including those with modulated frequency and multi-helicity. (^*)Supported by U. S. DOE Grant No. DE--FG02--86ER--53222