Reflectometry observation of density fluctuations associated with the resonant q=2 surface in Wendelstein VII-AS stellarator
Enhanced density fluctuations with the rational q = 2 (iota = 0.5) surface are observed by a microwave reflectometer in currentless NBI heated discharges with pellet injection at an edge iota of 0.52. Radial scan of MHD activity locates coherent density fluctuations at r/a = 0.7. Frequency and amplitude are estimated. Correlation between the level of the local density turbulence and the iota value during iota modulation at 300 Hz leads to the conclusion that the local enhancement of the broadband density turbulence exists at the points where the rational iota values are crossed. A phase jump in the turbulence modulation occurs for r/a = 0.7, indicating the location of the resonant iota = 0.5 surface. The effect can be the basis of a new method to analyse the evolution of the iota profile inside the plasma, with interesting applications in current control experiments.
Bibliographic Reference: Report: IPP 2/304 EN (1989) 27 pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
Record Number: 199010711 / Last updated on: 1994-12-01
Original language: en
Available languages: en