Monte Carlo guiding centre simulations of E x B  flow shear in edge transport barrier

E_r×B flow shear is simulated with a fully kinetic five-dimensional neoclassical Monte Carlo simulation both for JET and ASDEX Upgrade. Here, E_r is the radial electric field and B is the magnetic field. It is shown that high enough shear for turbulence suppression can be driven at low (L) to high (H) transition conditions without taking into account anomalous processes in E_r shear formation. For typical plasma parameters, at a certain edge temperature, shear is weaker in JET than in ASDEX Upgrade, thus requiring a higher edge temperature for L-H transition as observed also in experiments. However, although the simulation is carried out at experimentally observed L-H transition temperatures of each device, shear is still weaker in JET, which proposes that the critical shear in JET should be lower than in ASDEX Upgrade. The parametric dependence of the shear on temperature, density and magnetic field is investigated and the effects of density and temperature gradients, plasma current and the direction of the ∇B drift on the shear are discussed.