On the Influence of Probe Presheath on the Measurement of Fluctuation and E × B Turbulent Transport by Langmuir Probes

Abstract

AbstractThe influence of the probe's presheath region in the level of plasma fluctuations and E × B turbulent transport has been investigated in the plasma edge region of the stellarator TJ‐II using a multi array of Langmuir and Mach probes. Simultaneous measurements of plasma fluctuations carried out by probes located in and out the probe body sheath show similar results in the normalized level of fluctuations in the ion saturation current. However, floating potential fluctuations measured in the co and counter direction of the magnetic field on the sheath probe body show slight but significant differences. The local radial electrostatic turbulent driven transport measured in and out of the probe body sheath show consistent results, within the errors bars due to uncertainties in the determination of the effective probe collecting area. These results and previous findings call into a question the recent interpretation of probe measurements on the basis of the influence of the probe's presheath zone (B. Labombard, Plasma Phys. and Cont. Fusion 9(2002) 1300). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)