Characteristics of fluctuations in the equatorial and polar directions of a compact dipole plasma driven at steady state
The fluctuations in the plasma potential ( Vs̃) and electron density ( Nẽ) are measured in the steady-state dipole plasma confined in a spherical vacuum chamber using a single permanent dipole magnet. Measurements are made from a radial distance r = 0.5–17 cm, from the surface of the magnet in the...
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Veröffentlicht in: | Physics of plasmas 2024-09, Vol.31 (9) |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | The fluctuations in the plasma potential (
Vs̃) and electron density (
Nẽ) are measured in the steady-state dipole plasma confined in a spherical vacuum chamber using a single permanent dipole magnet. Measurements are made from a radial distance r = 0.5–17 cm, from the surface of the magnet in the equatorial (
θ=90°) and polar (
θ=180°) directions, using a 4-pin probe setup, and have been characterized by power spectra, cross-phase, cross-coherence, induced transport, and energy spectra. The fluctuations are stronger near the surface of the dipole magnet for
θ=90°, thereafter their magnitude decreases gradually with the radial distance. However, a peaked profile of potential fluctuations with the peak around r = 9 cm is observed for
θ=180°. The locations of strong fluctuations are around the locations of smaller values of the electron neutral collision frequency. Frequency-resolved power spectra show that the fluctuations in the dipole plasma, predominantly, belong to the very low-frequency range. The values of cross-phase (
≤45°) and
|Vs̃/Te|/|Nẽ/Ne|≤1 indicate the presence of drift wave instability in both planes, where
Te and
Ne are equilibrium values of the electron temperature and density. The radial variation of fluctuation-induced electron flux (
Γr) verifies the “inward diffusion” of electrons in the equatorial plane. |
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ISSN: | 1070-664X 1089-7674 |
DOI: | 10.1063/5.0207927 |