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Title: Spatiotemporal temperature fluctuation measurements by means of a fast swept Langmuir probe array

Abstract

Stationary Langmuir probe measurements of ion saturation current and floating potential in a plasma cannot give direct information on density and plasma potential fluctuations in the presence of temperature fluctuations. This problem can be avoided if the probe bias voltage is continuously swept faster than the fluctuation time scale, recording the current-voltage characteristic. This article reports the development of a spatiotemporal highly resolving Langmuir probe array with 15 fast swept tips, operating in the strongly magnetized, collisionless edge plasma of the Wendelstein 7-AS stellarator [Plasma Phys. Controlled Fusion 31, 1579 (1989)]. The probe tips are aligned in the poloidal direction, the tip spacing is 2 mm, and the sweeping frequency is 1.4 MHz. Current and voltage data are sampled with 50 MHz. The high bandwidth of the measurement is achieved by placing miniaturized differential amplifiers close to the probe tips in order to do an impedance transform. The surface-mounting technology and an additional inverse feedback module are utilized, allowing for an input voltage range of {+-}100 V, and a common mode rejection rate of 55 dB at 4 MHz, which is sufficient to resolve the nonlinear probe characteristic. For the evaluation of the data, a fit model for stationary probesmore » is employed and found adequate. Changes of the plasma parameters during one voltage sweep are taken into account by a linear interpolation of the fit parameters. Spatio-temporal fluctuation data gained by a fast swept Langmuir probe array, which can be relevant for the turbulent radial transport of particles and energy, are presented.« less

Authors:
; ;  [1]
  1. Max-Planck-Institut fuer Plasmaphysik, Wendelsteinstrasse 1, Greifswald 17491 (Germany)
Publication Date:
OSTI Identifier:
20953443
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 78; Journal Issue: 5; Other Information: DOI: 10.1063/1.2740785; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AMPLIFIERS; BOUNDARY LAYERS; ELECTRIC CURRENTS; FLUCTUATIONS; INTERPOLATION; LANGMUIR PROBE; MHZ RANGE 01-100; NONLINEAR PROBLEMS; PLASMA; PLASMA DENSITY; PLASMA POTENTIAL; STELLARATORS

Citation Formats

Schubert, M., Endler, M., and Thomsen, H.. Spatiotemporal temperature fluctuation measurements by means of a fast swept Langmuir probe array. United States: N. p., 2007. Web. doi:10.1063/1.2740785.
Schubert, M., Endler, M., & Thomsen, H.. Spatiotemporal temperature fluctuation measurements by means of a fast swept Langmuir probe array. United States. doi:10.1063/1.2740785.
Schubert, M., Endler, M., and Thomsen, H.. Tue . "Spatiotemporal temperature fluctuation measurements by means of a fast swept Langmuir probe array". United States. doi:10.1063/1.2740785.
@article{osti_20953443,
title = {Spatiotemporal temperature fluctuation measurements by means of a fast swept Langmuir probe array},
author = {Schubert, M. and Endler, M. and Thomsen, H.},
abstractNote = {Stationary Langmuir probe measurements of ion saturation current and floating potential in a plasma cannot give direct information on density and plasma potential fluctuations in the presence of temperature fluctuations. This problem can be avoided if the probe bias voltage is continuously swept faster than the fluctuation time scale, recording the current-voltage characteristic. This article reports the development of a spatiotemporal highly resolving Langmuir probe array with 15 fast swept tips, operating in the strongly magnetized, collisionless edge plasma of the Wendelstein 7-AS stellarator [Plasma Phys. Controlled Fusion 31, 1579 (1989)]. The probe tips are aligned in the poloidal direction, the tip spacing is 2 mm, and the sweeping frequency is 1.4 MHz. Current and voltage data are sampled with 50 MHz. The high bandwidth of the measurement is achieved by placing miniaturized differential amplifiers close to the probe tips in order to do an impedance transform. The surface-mounting technology and an additional inverse feedback module are utilized, allowing for an input voltage range of {+-}100 V, and a common mode rejection rate of 55 dB at 4 MHz, which is sufficient to resolve the nonlinear probe characteristic. For the evaluation of the data, a fit model for stationary probes is employed and found adequate. Changes of the plasma parameters during one voltage sweep are taken into account by a linear interpolation of the fit parameters. Spatio-temporal fluctuation data gained by a fast swept Langmuir probe array, which can be relevant for the turbulent radial transport of particles and energy, are presented.},
doi = {10.1063/1.2740785},
journal = {Review of Scientific Instruments},
number = 5,
volume = 78,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}