Enhanced particle confinement and turbulence reduction due to E x B shear in the TEXTOR tokamak

Positive radial electric fields have been created at the edge of the TEXTOR tokamak plasma using an electrode. The electric field induces a thin (delta r similar to 1.5 cm), E x B driven layer at the edge rotating poloidally at 12-20 km/s and featuring high shear. Concomitant changes in the density and poloidal electric field fluctuations and their cross-phase in the shear layer result in suppression of radial turbulent particle transport, even at low radial electric field strength. Temperature fluctuations are reduced, resulting in diminished turbulent heat flux. As turbulent particle transport is quenched, the particle confinement time tau(p) increases by a factor of 2 and the energy confinement time tau(E) by 20%. Turbulent transport accounts for similar to 50% of the total particle flux. Both the cross-phase and the density fluctuations are sensitive to the sign of del E-r.