Experimental evidence for gradient length-driven electron transport in tokamaks

Energy transport by the electrons in a tokamak is examined in steady-state and power modulation experiments using electron cyclotron heating. The resu lts are consistent with the assumption that temperature profiles are limite d by a critical gradient length, leading to "stiff" profiles. The modulatio n experiments show that the stiffness factor increases with temperature. Th ey strongly suggest that turbulence driven by the electron temperature grad ient may be a dominant mechanism of electron transport. Although possibly n ot universal, these results are valid under various plasma conditions.