Fluctuations, shearedradial electric fields and transport interplay in fusionplasmas

Abstract

Aview of recent experimental results and progress in thecharacterization of plasma turbulence in magnetically confineddevices is given. An empirical similarity in the scalingproperties of the probability distribution function ofturbulent transport has been observed in the plasma edge region. This result supports the view that turbulent transportdisplays universality in fusion plasmas and emphasizes theimportance of the statistical description of transportprocesses in fusion plasmas as an alternative approach to thetraditional way of characterizing transport based on thecomputation of effective transport coefficients. Comparativestudies in different magnetically confined plasmas show thatfluctuations and sheared poloidal flows organize themselves tobe close to marginal stability. This property should beconsidered as a critical test for improved confinement transition models. Magnetic configuration scan experiments instellarator devices have shown a complex interplay betweentransport and sheared radial electric fields in the proximityof rational surfaces. The development of new fluctuationanalysis techniques based on the investigation of velocity fluctuations opens a new way to investigate turbulent transportand dynamical electric fields in the plasma core region.