The Dynamics of Short-Scale Turbulent Fluctuations During The H–L Back Transition in The EAST Superconducting Tokamak
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The dynamics of the turbulent fluctuations during the H–L back transition have been studied on EAST by a CO2 laser collective scattering system. The limit-cycle oscillation (LCO) regime has been frequently observed during the H–L back transition, and the oscillation frequency increases gradually as the back transition is approached. In the LCO regime, both the core and outer fluctuation level have a gradual increase, and reach a maximum near the back transition to L-mode, which mainly result from the appearance and enhancement of a low-frequency (10–20 kHz) quasi-coherent structure. The cross-spectrum analysis suggests that the QC structure could propagate from the core to the outer region.
KeywordsH–L back transition Turbulent fluctuations Collective scattering Quasi-coherent structure
One of the authors (Cao) thanks the useful discussions with H. Q. Wang. This work was supported by the National Nature Science Foundation of China with Contracts Nos. 10975159, 11275232.