OBSERVATION OF A LOCALIZED TRANSITION FROM EDGE TO CORE DENSITY TURBULENCE IN THE TFTR TOKAMAK

A localized transition zone is observed between turbulent, long-wavele ngth density fluctuations (k(perpendicular-to) < 2 cm-1) in the core a nd edge of beam-heated discharges in TFTR. The core turbulence is unim odal while the edge has two counterpropagating modes, both of which ar e spectrally distinct from the core fluctuations. The fluctuation ampl itude in the core scales with the global energy confinement time while in the edge it does not. These observations suggest that distinct mod es are responsible for turbulence in the two regions and that only the core mode is directly related to global confinement.