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(THP2/13) Theory of Enhanced Core Confinement Regimes in Tokamaks

   
G. M. Staebler , R. E. Waltz , and C. M. Greenfield 
General Atomics, P.O. Box 85608, San Diego, California 92186-5608
 
B. W. Stallard 
Lawrence Livermore National Laboratory, Livermore, California

Abstract
A comparison of two types of DIII-D  plasmas with improved core ion thermal transport is made. One is an H-mode  edge weak magnetic shear discharge and the other is an L-mode  edge negative central shear plasma. It is found that the region of reduced ion thermal transport is consistent with the region where theory predicts stability of ion temperature gradient modes in both cases. The electron thermal transport remains anomalously high throughout the plasma. The electron transport may be caused by the presence of electron temperature gradient modes in the outer part of the plasma. The modes are found to be linearly unstable even into the region of high $\rm E \times B$ shear. In the central core no drift-ballooning modes  are found to be unstable. The negative central shear case is predicted to be unstable to resistive interchange modes in the reversed shear  region.

   

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