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Comparative Experimental Study of Large-Scale Fluctuations in a Toroidally Mgnetized Low-Beta Plasma

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Final rept. 15 Apr 2001-31 Mar 2002

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A comparative experimental study of large-scale space-time structures embedded into the broad-band multi-scale turbulent plasma fluctuations of the purely toroidally magnetized experiment TEDDI is presented. Two different plasma sources are compared Plasma can be produced either by a thermionic discharge or by inductive heating by a helicon antenna. Turbulent plasma potential and plasma density fluctuations were analyzed by conditional averaging. It turned out that large-scale space-time structures develop on both plasmas, which propagate with local E x B drift. A contribution of diamagnetic drifts is not observed. In the thermionic discharge dipole-like density structures are found, in the helicon discharge the detected structures are generally of monopole-like shape and are considerably sized when compared to the thermionic discharge. Direct measurements of the fluctuation induced transport can be related to the specific properties of the detected large-scale fluctuation structures. It is concluded that the injection of the negative space charge via the heated filament greatly alters the properties of the turbulent fluctuations. Although the basic statistical properties are substantially unaffected by the plasma source a strong influence on the formation of large-scale fluctuation structures and the associated transport is found.

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  • Plasma Physics and Magnetohydrodynamics

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