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Characteristics of an axisymmetric magnetic oscillation closely related to L-H transition on experimental advanced superconducting tokamak (EAST)

An axisymmetric magnetic oscillation (AMO) of 5–10 kHz in the L-mode plasma edge has been studied on an experimental advanced superconducting tokamak. The analysis shows that this oscillation only occurs at the plasma very close to the L-H transition. The structure of magnetic oscillation is axisymmetric (n = 0) toroidally and demonstrates an m = 2 standing wave in the poloidal direction. The density fluctuation of AMO measured by reflectometry at the midplane is nearly in phase, indicating that the AMO is not a radial traveling wave. The AMO shows an obvious modulation effect on the background magnetic/density fluctuation, and as a result, the edge density/density gradient and particle flux onto the divertor are also modulated by the AMO. The frequency scaling of the AMO is f m ∝ ( ∇ n e / I p 2 ) − 1. The bicoherence analyses show a strong nonlinear interaction between the AMO and the background turbulence, and other nonlinear interactions between the AMO and three other coherent fluctuations with frequencies (∼4, ∼11, and ∼15 kHz) are also found.An axisymmetric magnetic oscillation (AMO) of 5–10 kHz in the L-mode plasma edge has been studied on an experimental advanced superconducting tokamak. The analysis shows that this oscillation only occurs at the plasma very close to the L-H transition. The structure of magnetic oscillation is axisymmetric (n = 0) toroidally and demonstrates an m = 2 standing wave in the poloidal direction. The density fluctuation of AMO measured by reflectometry at the midplane is nearly in phase, indicating that the AMO is not a radial traveling wave. The AMO shows an obvious modulation effect on the background magnetic/density fluctuation, and as a result, the edge density/density gradient and particle flux onto the divertor are also modulated by the AMO. The frequency scaling of the AMO is f m ∝ ( ∇ n e / I p 2 ) − 1. The bicoherence analyses show a strong nonlinear interaction between the AMO and the background turbulence, and other nonlinear interactions between the AMO and three other coherent fluct...