FLUCTUATIONS AND ASSOCIATED TRANSPORT IN THE L MODE IN TORE-SUPRA

A parametric experimental study of fluctuations has been performed in L-mode plasmas during steady-state phases in Tore Supra. Simultaneous measurements of density and magnetic fluctuations in the gradient regi on of the discharge show that both components are strong functions of the local electron temperature decreasing lengths. The wavenumber spec trum of density fluctuations is obtained with the CO2 scattering diagn ostic both in the bulk and at the edge of the discharge. In the bulk, in the L-mode compared to ohmic plasmas, the k spectrum increases belo w k = 7 cm(-1) and is globally shifted towards low k values. At the ed ge (r/a > 0.9) an increase on all k values is observed. At r/a = 0.5, the level of both types of fluctuations is found to be linearly correl ated with the local heat diffusivity chi(e). The heat flux ratio advec ted by electrostatic eddies in the bulk of the discharge is estimated by using fluctuation measurements and generic predictions for the para metric dependency of the thermal flux. The calculated level of density fluctuation necessary to account for the heat transport at midradius is found to be compatible with values measured in other tokamaks. It i s also found that the heat flux ratio behaviour conducted by electrost atic fluctuations is compatible with most of the experimental heat flu x ratio behaviour in the plasma core (0.4 < r/a < 0.6). This property does not hold at the edge of the plasma (r/a = 0.7). The similar param etric dependency of magnetic and density fluctuation level does not al low one to make a clear statement about their relative importance in t he transport process and suggests that they could be coupled.