Influence of temperature fluctuations on plasma turbulence investigations with Langmuir probes

Abstract

The reliability of Langmuir probe measurements for plasma-turbulence investigations is studied on GEMR gyro-fluid simulations and compared with results from conditionally sampled I-V characteristics as well as self-emitting probe measurements in the near scrape-off layer of the tokamak ASDEX Upgrade. In this region, simulation and experiment consistently show coherent in-phase fluctuations in density, plasma potential and also in electron temperature. Ion-saturation current measurements turn out to reproduce density fluctuations quite well. Fluctuations in the floating potential, however, are strongly influenced by temperature fluctuations and, hence, are strongly distorted compared to the actual plasma potential. These results suggest that interpreting floating as plasma-potential fluctuations while disregarding temperature effects is not justified near the separatrix of hot fusion plasmas. Here, floating potential measurements lead to corrupted results on the ExB dynamics of turbulent structures in the context of, e.g., turbulent particle and momentum transport or instability identification on the basis of density-potential phase relations.

References in corpus (2)

• Nonlinear polarisation and dissipative correspondence between low frequency fluid and gyrofluid equations
• Analysis of the temperature influence on Langmuir probe measurements on the basis of gyrofluid simulations

Cited by in corpus (8)

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• L-mode filament characteristics on MAST as a function of plasma current measured using visible imaging
• New insights on divertor parallel flows, ExB drifts, and fluctuations from in situ, two-dimensional probe measurement in the Tokamak à Configuration Variable