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Experimental observation of resonance manifold shrinking under zonal flow shear

: Ullmann, T.; Schmid, B.; Manz, P.; Milligen, B. Van; Tovar, G.E.M.; Ramisch, M.


Physical Review. E 102 (2020), Art. 063201
ISSN: 1063-651X
ISSN: 1539-3755
ISSN: 2470-0045
ISSN: 2470-0053
ISSN: 1550-2376
European Commission EC
H2020; 633053; EUROfusion
Journal Article
Fraunhofer IGB ()

In two-dimensional turbulent systems the redistribution of energy can be described by quadratic nonlinear three-wave interactions, which are limited by resonance conditions. The set of coupling modes can be understood as resonant manifold. It has been predicted by theory that, in the presence of a shear flow, the resonant manifold in wave-number space shrinks in time favoring large-scale structures. The phenomenon of manifold shrinking in the presence of shear flows is studied the first time experimentally in drift wave turbulence at the stellarator TJ-K by bicoherence analysis. By estimating effective mode numbers characterizing the width of the manifold, it is demonstrated that increasing shear leads to a shrinking of the resonance manifold.