Spectroscopic interpretation and velocimetry analysis of fluctuations in a cylindrical plasma recorded by a fast camera

Abstract

Fast visible imaging is used on a cylindrical magnetized argon plasma produced by thermionic discharge in the Mirabelle device. To link the information collected with the camera to a physical quantity, fast camera movies of plasma structures are compared to Langmuir probe measurements. High correlation is found between light fluctuations and plasma density fluctuations. Contributions from neutral argon and ionized argon to the overall light intensity are separated by using interference filters and a light intensifier. Light emitting transitions are shown to involve a metastable neutral argon state that can be excited by thermal plasma electrons, thus explaining the good correlation between light and density fluctuations. The propagation velocity of plasma structures is calculated by adapting velocimetry methods to the fast camera movies. The resulting estimates of instantaneous propagation velocity are in agreement with former experiments. The computation of mean velocities is discussed.

Flow dynamics and magnetic induction in the von-Kármán plasma experiment

“…Preliminary results related to the dynamics of low-frequency waves at the edge of the plasma column have been obtained with a high-speed camera (Photron SA-5). High-speed imaging (around 10 5 images/s at a resolution 200 × 200 px) allows to probe the global spatio-temporal dynamics of plasma density fluctuations (Oldenbürger et al 2010). Ion velocimetry from Laser Induced Fluorescence of Argon ions (ArII) lines will shortly be installed to probe the details of the plasma flows with non-intrusive diagnostics (Demtröder 1981;Bieber et al 2011).…”

“…In particular, the role of large-scale controlled flows on effective small-scale cross-field transport can be addressed. Fast imaging camera and probe-arrays will be used to probe the spatio-temporal dynamics of plasma fluctuations (Oldenbürger et al 2010). …”

“…In most of these investigations, rotation of the plasma column is achieved by biasing cold limiters, rings or portions of the vacuum vessel. In these studies, the influence of radial plasma flow shear on interchange instability (Teodorescu et al 2006), drift wave instabilities (Klinger et al 1997), turbulent transport (Wallace et al 2004;Schaffner et al 2012;Zhou et al 2012), plasma confinement (Fredriksen et al 2006) or radial transport (Oldenbürger et al 2010;Annaratone et al 2011) has been detailed. Our flow driving scheme will allow to drive plasma rotation in both directions and to extend some of the previous studies in cases with an axial shear of the rotation of the plasma column.…”

Investigating flow patterns and related dynamics in multi-instability turbulent plasmas using a three-point cross-phase time delay estimation velocimetry scheme

“…Other PTV methods are also capable of measuring the instantaneous velocity field of propagating wave-like structures in a plasma. 20,21 Ref. 22 is a detailed study of optical flow and pattern matching techniques introducing a hybrid approach between cross-correlation and pattern matching.…”

Spatiotemporal Splitting of Global Eigenmodes due to Cross-Field Coupling via Vortex Dynamics in Drift Wave Turbulence

“…E × B-vorticity fluctuations (Ω = ∇ ×ṽ E×B ) are measured with a 3×3 probe array [21] and are associated with light intensity fluctuations (zero-lag correlation values of ≈ 0.5 − 0.8). Light fluctuations represent the dynamics of density fluctuations [25] and the dynamics ofẼ × Bvorticity [26].…”