Investigation of the perpendicular dynamics of drift-wave turbulence in a toroidal plasma with multi-probe arrays

The microscopic structure of drift-wave turbulence perpendicular to the magnetic field is investigated in a toroidal plasma by means of multi-probe arrays. The dependence of structure sizes on the drift-scale rho(s) is studied with the objective of classifying the range of perpendicular wavenumbers k(perpendicular to)rho(s) with respect to the analytical linear drift-wave dispersion relation. Wavenumbers in the range 0.2-1.5 are found according to a scaling around k(perpendicular to) similar to rho(-1/2)(s). Values k(perpendicular to)rho(s) < 0.3, for which a dispersion-free dynamics is expected, are found in H and D. Biasing experiments on discharges in this range show that very strong E x B flow shear changes the characteristic mode structure in favour of coherent large-scale structures, which can be related to local turbulent inward transport as a result of modifications in the phase relation between density and potential fluctuations.