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P: Plasmaphysik

P 9: Magnetischer Einschluss, Fusionsplasmen

P 9.4: Talk

Tuesday, March 19, 2002, 17:25–17:40, HZO 60

Active Probing Experiments in Wendelstein 7-AS stellarator — •Henning Thomsen, T. Klinger, and M. Endler — Max-Planck-Institut für Plasmaphysik, EURATOM Association, Germany

In recent experiments on Wendelstein 7-AS stellarator, the propagation parallel and perpendicular to the confining magnetic field of sine signals in the drift frequency range 1-100 kHz were studied by means of extensive Langmuir probe diagnostics [1]. In contrast to previous findings in tokamaks [2,3], an asymmetry of the parallel propagation was not observed. Perpendicular to the magnetic field, the propagation is determined by the background E×B-plasma rotation. As an advanced approach, spatio-temporal wave patterns were injected into the edge plasma. Such a technique was recently used in a magnetized low-temperature plasma and a strong influence on the plasma turbulence, i.e. a mode-selective synchronization, was found [4]. On the contrary, in Wendelstein 7-AS stellarator the imposed waves do not show a dramatic effect on the plasma turbulence. Nonetheless, the injected waves can be seen as ‘test waves’ in a turbulent background. These waves can co- or counter-propagate with respect to the background plasma rotation. The coupling strength of the imposed wave patterns to the background turbulence relies on the match of the imposed waves to the dynamics of turbulent structures.

[1] H. Thomsen, et al., Czech. J. Phys.,51, 1079 (2001)

[2] T. Uckan et al., Nucl. Fusion, 35, 487 (1995)

[3] Z. Kan et al., Phys. Plasmas, 4, 2237 (1997)

[4] C. Schroeder et al., Phys. Rev. Letters, 86, 5711 (2001)