Turbulence measurements and local transport analysis in dedicated β scan in Tore-Supra L-mode discharges.

The ITER H-mode scaling law written in dimensionless form [1] predicts a degradation of the energy confinement with β (the ratio of the kinetic to the magnetic pressure):B0τHE ∝ β−0.9. However dedicated experiments on JET [2] and DIII-D [3] have shown a very weak dependence with β while the JT-60U [4] results are closer to the original ITER scaling law. This contradic-tion remains unexplained. One possible explanation comes from ELMs, which are likely MHD modes and thus depend on β. To clarify this question, a β scaling experiment has been achieved in L-mode plasmas on Tore-Supra. These experiments are not subject to ELMs, as these relax-ation oscillations are not present in L-mode plasmas. In addition to global analysis, supported by transport calculations from the integrated modelling CRONOS code [6], turbulence has been studied with reflectometry. Thus, we will present the β dependence through global measure-ments (with τE) and local analysis (with the heat diffusivity χ and density fluctuations δn/n). We consider here the usual form of the dimensionless scaling analysis, which assumes that normalised transport coefficients only depend on the local dimensionless parameters ρ∗, β and ν ∗ [5]. Moreover it is also assumed that the thermal diffusivity can be written as a power law: χ = χBρ