Density, temperature, and potential fluctuation measurements by the swept Langmuir probe technique in Wendelstein 7-AS
- Max Planck Institut fuer Plasmaphysik, EURATOM-IPP Association, D-85748 Garching (Germany)
In the Wendelstein 7-AS stellarator (W7-AS) [Plasma Phys. Controlled Fusion [bold 33], 1591 (1991)], current-voltage characteristics of the Langmuir probe at sweep frequencies in the range 400 kHz to 1 MHz were measured and it was found that the mean and fluctuation values of the ion saturation current, floating potential, and electron temperature were independent of the sweep frequency. A radial scan in the vicinity of the velocity shear layer was performed. The simultaneous sweeping of 3 probe tips showed a statistically significant spatial coherence of the fluctuations in the poloidal direction and a decrease in spatial coherence of the fluctuations with increasing tip separation could be demonstrated. The observation of a change in the propagation direction of fluctuations as the shear layer was crossed and a calculation of the transport spectrum show that the swept probe method is capable of reproducing known results. Apparent temperature fluctuations, due to variations of density and potential during a sweep, are shown by simulations to be only of importance at frequencies above half the Nyquist frequency.
- OSTI ID:
- 6687241
- Journal Information:
- Physics of Plasmas; (United States), Vol. 1:11; ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
STELLARATORS
PLASMA DIAGNOSTICS
ELECTRON TEMPERATURE
FLUCTUATIONS
LANGMUIR PROBE
PLASMA DENSITY
POTENTIALS
TEMPERATURE MEASUREMENT
CLOSED PLASMA DEVICES
ELECTRIC PROBES
PROBES
THERMONUCLEAR DEVICES
VARIATIONS
700320* - Plasma Diagnostic Techniques & Instrumentation- (1992-)