Laser blow-off injected impurity transport in L mode Tore Supra plasmas

Metal impurity ions have been injected in Tore Supra discharges by laser blow-off. The ion transport is studied by means of an impurity ion transport code; the radial profiles of the diffusion coefficient D and of the inward convection velocity V are obtained by simulating soft X ray brightness and emissivity time evolutions. Three different experimental situations are considered: a discharge with sawteeth stabilized by LH heating, a high-n(e) discharge with ICR heating and a strongly sawtoothing discharge with combined ICR and LH heating. In all cases, the simulations show the presence of two transport regions, the central core having reduced transport coefficients, and the outer region where there is the necessity to increase transiently the diffusion coefficient D during the first few milliseconds after the injection. It has been previously suggested that the shear s = 0.5 is the critical physical parameter governing the transition from low to high transport coefficients. The s = 0.5 criterion seems satisfied in the first two cases, whereas the closeness of the s = 0.5 and q = 1 surfaces does not allow a conclusion to be made in the combined heating case.