Turbulence Behaviour During Electron Heated Reversed Shear Discharges in JET

Low frequency/long wavelength density turbulence is found to be reduced within the volume enclosed by an electron thermal Internal Transport Barrier (e-ITB) generated with lower hybrid microwave heating in the JET tokamak. The turbulence reduction coincides with a region (typically r/a < 0.4) of negative, or reversed magnetic shear s and reduced electron thermal diusion χe. In the tokamak edge region (r/a > 0.8) large positive magnetic shear s > 1 is also found to reduce the turbulence amplitude. Estimates of the core turbulence wavelengths (λ⊥ > 0.1 m) are not in agreement with expectations from Electron Temperature Gradient (ETG) instabilities.