Analysis of large and small scale flucuations in the plasma edge of ASDEX Upgrade

Introduction Large and small scale fluctuations of both electron density and temperature are accessible by the Thomson scattering system on ASDEX Upgrade [1] in the steep edge gradient region of H mode plasmas: The characteristic structures and spatial distributions of large scale fluctuations which exist during and in between Edge Localised Modes (ELMs) were investigated by 2D snapshots of the electron density and temperature in the poloidal plane [2, 3]. Small scale fluctuations between ELMs are inferred indirectly in the steep gradient region by measuring the gradient lengths Lne and LTe of the 1D radial electron density and temperature profiles, respectively. The deduced parameter ηe Lne LTe was identified as a critical parameter in theoretical calculations of the fluctuations induced by electrons. Several values for ηe were found on ASDEX Upgrade for different plasma parameters [5]. The variation of the mean amplitudes of the large scale fluctuations and of the parameter ηe with plasma parameters for type I ELMy discharges is investigated in this paper. Experimental Setup