PRESSURE-DRIVEN HIGH-N HIGH-M TEARING MODES IN LOW SHEAR REGIONS WITHHIGH-PRESSURE GRADIENTS AND HIGH-RESISTIVITY/

High-n modes near q = 1 observed in ASDEX Upgrade discharges with high impurity accumulation have been shown to be tearing modes. High-n tea ring modes are usually stable; however, owing to high current gradient and low shear they become unstable. The coupling of different poloida l harmonics due to toroidal geometry and plasma shaping supports the m ode growth. Changes in the pressure alter the relationship between the various sideband harmonics within one mode even to the extent that it s tearing character may be destroyed.