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)
Hauptverfasser: Hunjan, Sargam, Bhattacharjee, Sudeep
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description 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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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. 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subjects Dipoles
Electron density
Electron energy
Electron flux
Energy spectra
Frequency ranges
Plasma
Power spectra
Spherical plasmas
Steady state
Vacuum chambers
title Characteristics of fluctuations in the equatorial and polar directions of a compact dipole plasma driven at steady state
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