Abstract
Anomalous transport due to large coherent structures, or coherent events, is studied experimentally in a magnetized toroidal discharge plasma. The present analysis emphasizes anomalous plasma losses as well as transport of electron thermal energy density across magnetic field lines. The experiment was carried out in the Blaamann device at the University of Tromsø. The diagnostics are based on data for potential, density and electron temperature variations as detected by Langmuir probes. Most of the data analysis uses conditional sampling. The flux of thermal energy density can be broken down into several components which are analyzed separately. Experimental means for obtaining the space-time variation of the complete polarization drifts are demonstrated, and the results compared with the fluctuating -velocities. For the present conditions these polarization drifts contribute only little to the plasma losses, but for other discharge parameters in heavier gases they can be important. Our results show that while the density, the potential and the electric field variations are dominated by large scales, the vorticity of the -flow as well as the ion polarization drifts are strongly intermittent.
Highlights
Plasma losses due to large amplitude fluctuations characterize a number of laboratory devices, and similar features can be observed in nature as well
In the present work we present data from the toroidal Blaamann device at the Arctic University of Tromsø [1], where a discharge plasma is confined by a simple toroidal magnetic field B0 with a possibility for adding a small vertical magnetic field
The results presented in the following refer to one particular device, but they are relevant for other similar experiments [2,3,4,5]
Summary
Plasma losses due to large amplitude fluctuations characterize a number of laboratory devices, and similar features can be observed in nature as well These phenomena have been studied intensively in part because of their importance for controlled thermonuclear fusion experiments. The thermal energy density, which is studied in the present work, is given as (n + n0)(Te + Te0), where the electron temperature is Te >> Ti, assuming the ions to be cold. The flux of this quantity is Y + Y0 ≡ (Te + Te0)(Γ +. Particular attention will be given to the space time evolution of the term TeΓ ≡ Te(n0u + nu0 + nu − nu)
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