TURBULENT FLUCTUATIONS IN TFTR CONFIGURATIONS WITH REVERSED MAGNETIC SHEAR

Turbulent fluctuations in plasmas with reversed magnetic shear have be en investigated on the Tokamak Fusion Test Reactor. Under intense auxi liary heating, these plasmas are observed to bifurcate into two states with different transport properties. In the state with better confine ment, it has been found that the level of fluctuations is very small t hroughout most of the region with negative shear. By contrast, the sta te with lower confinement is characterized by large bursts of fluctuat ions which suggest a competition between the driving and the suppressi on of turbulence. These results are consistent with the suppression of turbulence by the E x B velocity shear.