Measurement of the correlation spectrum of electrostatic potential fluctuations in an ECRH Helimak plasma

Journal Article · Wed Sep 01 00:00:00 EDT 1993 · Journal of Fusion Energy; (United States)

DOI:https://doi.org/10.1007/BF01079672· OSTI ID:5090025

Zimmerman, E D; Luckhardt, S C ^[1]

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1. MIT Plasma Fusion Center, Cambridge, MA (United States)

Measurements of the length and time scales of turbulent potential fluctuations were carried out on the MIT Versatile Toroidal Facility (VTF). Plasmas were produced by ECRF heating in a novel toroidal configuration which the authors have termed the Helimak. The configuration consists of a toroidal field B[sub [phi]] of approximately 800 gauss and a vertical field B[sub z] of typically 10 gauss, produced by a Helmholtz coil. T[sub e] is approximately 10 eV. The density exhibited a peaked profile having n[sub max] [approximately]2 [times] 10[sup 10] cm[sup [minus]3] and a density gradient scale length of [approximately]10 cm. The fluctuation experiments were conducted using a mobile vertical array of eight Langmuir probes. At major radii outside the density peak, the vertical correlation lengths [lambda][sub c][perpendicular] of fluctuations were found to be on the order of 5-10 cm for fluctuation frequencies below 3-8 kHz, and on the order of 1-2 cm at higher frequencies. At major radii on the inner slope of the density peak, a new feature appears in the spatial coherence function consisting of a second peak at a probe separation which scales linearly with vertical field. This observation indicates that these fluctuations have a correlation length on the order of 2[pi]R[sub o] [approximately]600 cm in the direction parallel to the helical magnetic field lines.

• OSTI ID: 5090025
• Journal Information: Journal of Fusion Energy; (United States), Vol. 12:3; ISSN 0164-0313
• Country of Publication: United States
• Language: English

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70 PLASMA PHYSICS AND FUSION TECHNOLOGY
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ECR HEATING
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PLASMA WAVES
CORRELATIONS
FLUCTUATIONS
ANNULAR SPACE
CLOSED CONFIGURATIONS
CONFIGURATION
HEATING
HIGH-FREQUENCY HEATING
MAGNETIC FIELD CONFIGURATIONS
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