Electron Profile Stiffness and Critical Gradient Studies in an L-mode Discharge in DIII-D

Several heat flux scans have been performed in an L-mode discharge in DIII-D with the goal of investigating the stiffness and critical gradient in the electron channel at $\rho=0.6$, 0.4 and 0.3. The heat flux scans employed 6 gyrotrons operating for 3.5~s with a shot-by-shot variation in heat flux achieved by moving 1 gyrotron/shot from just outside to just inside the region of interest. The stiffness was studied as a function of 4 different toroidal rotation conditions, low rotation with ECH only, higher rotation with co-NBI and counter-NBI, and lower rotation with balanced-NBI. Preliminary results indicate that toroidal rotation does not appear to play a strong role in determining the stiffness of the electron profile. For the ECH only condition at $\rho=0.6$ very low values of temperature gradient were obtained, well below the critical gradient estimated by the gradient where the heat flux projects to zero.