Observation of density fluctuations associated with the resonant q = 2 surface in the Wendelstein VII-AS stellarator
| Autor: | H. J. Hartfuss, E. Anabitarte, ECRH-Group, J. Sanchez |
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| Rok vydání: | 1990 |
| Předmět: | |
| Zdroj: | Nuclear Fusion. 30:2383-2391 |
| ISSN: | 1741-4326 0029-5515 |
| DOI: | 10.1088/0029-5515/30/11/014 |
| Popis: | Enhanced density fluctuations associated with the rational q = 2 (l = 0.5) surface have been observed by microwave reflectometry in currentless discharges heated by neutral beam injection, with pellet injection at an edge value of the rotational transform l of 0.52. A radial scan of the MHD activity located the coherent density fluctuations at r/a = 0.7. The frequency and amplitude of these fluctuations have been estimated. The correlation between the level of the local density fluctuation and the l value during l modulation at 300 Hz leads to the conclusion that the broadband density fluctuation is enhanced at the points where the rational l values are crossed. A phase jump in the turbulence modulation occurs for r/a = 0.7, indicating the location of the resonant l = 0.5 surface. This effect can become the basis of a new method to analyse the evolution of the l profile inside the plasma, with interesting applications to current control experiments, especially in low shear configurations. |
| Databáze: | OpenAIRE |
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