Role of turbulence and electric fields in the formation of transport barriers and the establishment of improved confinement in tokamak plasmas through inter-machine comparison

Over the past decade new regimes of tokamak operation have been identified, whereby electrostatic and magnetic turbulence responsible for anomalous transport, can be externally suppressed, leading to improved confinement. Although turbulence measurements have been performed on many confinement devices, the insight gained from these experiments is relatively limited. To make further progress in the understanding of plasma turbulence in relation to improved confinement and transport barriers, an extensive experimental and theoretical research programme should be undertaken. The present INTAS project investigates the correlations between on the one hand the occurrence of transport barriers and improved confinement in the tokamaks TEXTOR & T-10 and Tore Supra as well as on the smaller-scale tokamaks FT-2, TUMAN-3M and CASTOR, and on the other hand electric fields, modified magnetic shear and electrostatic and magnetic turbulence using advanced diagnostics with high spatial and temporal resolution. This is done in a strongly coordinated way and exploiting the complementarity of TEXTOR and T-10 and the backup potential of the other tokamaks, which together have all the relevant experimental tools and theoretical expertise. Advanced theoretical models and numerical simulations are used to check the experimental results.