EXPERIMENTAL-EVIDENCE OF EDGE TURBULENCE DRIVEN BY MULTIPLE MECHANISMS IN ATF

The scaling properties of edge fluctuations have been investigated using Langmuir probes in the edge region of the Advanced Toroidal Facility (ATF). The fluctuations in the ion saturation current (I(s)/I(s)) and the transport inferred from the fluctuations increase with increasing density gradient, while the local electron temperature is kept unchanged. The modification of the electron temperature in the range 10-50 eV while keeping the density profile constant does not have any significant influence on I(s)/I(s). In regions where E(r)/B almost-equal-to 0, the poloidal phase velocity of the fluctuations is given by v(ph) almost-equal-to 2T(e)/L(n)B. More than one of the proposed mechanisms must be invoked to explain all the experimental observations.