The experimental investigation on the role of E x B The experimental investigation on the role of E x B flow shear in tilting and breaking turbulent eddies flow shear in tilting and breaking turbulent eddies I. Shesterikov 1 , Y. Xu 1 , С. Hidalgo 2 , S. Jachmich 1 , P. Dumortier 1 , M. Berte 1 , M. Vergote 1 , M. Van Schoor 1 , G. Van Oost 3 and the TEXTOR team 1 Laboratory for Plasma Physics, ERM / KMS, Brussels, Belgium 2 Laboratorio Nacional de Fusion, Association EURATOM-CIEMAT, 28040 Madrid, Spain 3 Department of Applied Physics, Ghent University, B-9000 Gent, Belgium
Outline Motivation Experimental Setup Impact of naturally sheared flow on turbulent eddies Impact of externally induced flow on turbulent eddies Geometry detection using the two-dimensional FFT Directional analysis using the 2D wavelet transformation Splitting events Multi-resolution Optical Flow and Reynold stress Conclusions
Outline Motivation Experimental Setup Impact of naturally sheared flow on turbulent eddies Impact of externally induced flow on turbulent eddies Geometry detection using the two-dimensional FFT Directional analysis using the 2D wavelet transformation Splitting events Multi-resolution Optical Flow and Reynold stress Conclusions
Motivation The effect of a sheared flow H. Biglari, P. H. Diamond and P. W. Terry, Phys. Fluids B2, 1 (1990)
Outline Motivation Experimental Setup Impact of naturally sheared flow on turbulent eddies Impact of externally induced flow on turbulent eddies Geometry detection using the two-dimensional FFT Directional analysis using the 2D wavelet transformation Splitting events Multi-resolution Optical Flow and Reynold stress Conclusions
TEXTOR Top View
Experimental Setup
Experimental Setup
Typical frames from GPI
Typical video from GPI
Outline Motivation Experimental Setup Impact of naturally sheared flow on turbulent eddies Impact of externally induced flow on turbulent eddies Geometry detection using the two-dimensional FFT Directional analysis using the 2D wavelet transformation Splitting events Multi-resolution Optical Flow and Reynold stress Conclusions
The impact of naturally sheared flow V edia V idi a V idi a V edia LCFS
The impact of naturally sheared flow 5% - Tilt Only We had analyzed 4959 images Among them in 19 discharges 30% - Tilt and Split Directly observed for the first time I. Shesterikov, Y. Xu et al., Nuclear Fusion 52, 042004 (2012).
The impact of naturally sheared flow Tilting and breaking eddies under the natural shear flow dV E r × B -1 E r x B flow shear rate ω s = ⋅ l cr l cθ dr ω D = 1 / τ c = 1.0 ⋅ 10 5 s − 1 Natural scattering rate 5 s − 1 ω s = 1.2 ⋅ 10 Tilt 5 s − 1 Tilt and Split ω s = 2.6 ⋅ 10 ω s Tilt = 1.2 ω D ω s Tilt and Split = 2.6 ω D
Outline Motivation Experimental Setup Impact of naturally sheared flow on turbulent eddies Impact of externally induced flow on turbulent eddies Geometry detection using the two-dimensional FFT Directional analysis using the 2D wavelet transformation Splitting events Multi-resolution Optical Flow and Reynold stress Conclusions
Biasing experiment H-mode transition
Biasing experiment H-mode transition
Biasing experiment Ohmic Biasing H-mode
Biasing experiment 2D Fourier Transform GPI Frame Ohmic No preferential orientation tg ( φ ) = k θ k r Biasing Preferential orientation
Biasing experiment ( 2D Fourier Transformation ) Ohmic Biasing H-mode
Biasing experiment ( Directional analysis ) Eddy № 25 Eddy № 26 Eddy № 27 Z [cm]
Biasing experiment ( Directional analysis ) cos ( θ ) +y ⋅ sin ( θ ) ) ) ⋅ exp ( − 1 2 ) 2 √ x Ψ M ( x,y,θ ) = exp ( ik 0 ( x ⋅ 2 +y 2D Morlet wavelet − 1 ∬ Ψ M ( ,θ ) I ( x,y ) dxdy x − a , y − b 2D Wavelet Transform W ( a,b,s,θ ) =s s s
Biasing experiment ( Directional analysis ) Ohmic Biasing H-mode No preferential No preferential preferential orientation orientation orientation
Biasing experiment ( splitting events ) Ohmic Biasing H-mode
Biasing experiment (o ptical Flow ) 2 ( V x ,V y ) = ∬ [ ∂ y ⋅ V y ] 2 ∂ E ∂ t + ∂ E ∂ x ⋅ V x + ∂ E ε b dxdy Typical video of Vector Field 2 ( V x ,V y ) = ∬ ( ∣∇ V x ∣ 2 ) + ( ∣∇ V y ∣ 2 ) dxdy ε c ∣∇ V x ∣ 2 = ( ∂ x ) 2 + ( ∂ y ) 2 ∂ V x ∂ V x ∣∇ V y ∣ 2 = ( ∂ x ) 2 + ( ∂ y ) 2 ∂ V y ∂ V y
Biasing experiment ( Reynold Stress ) <V r V θ > <V r V θ >
Biasing experiment ( Reynold Stress ) Y. Xu et al., PoP 16, 110704 (2009).
Biasing experiment ( Reynold Stress ) b 2 ( f 1, f 2 ) Ohmic Biasing b 2 ( f 1, f 2 )
Prior L-H transition Flow shear Tilting of eddies Symmetry breaking Generation of Reynold stress Low frequency Zonal Flow Helpful for L-H transition
Outline Motivation Experimental Setup Impact of naturally sheared flow on turbulent eddies Impact of externally induced flow on turbulent eddies Geometry detection using the two-dimensional FFT Directional analysis using the 2D wavelet transformation Splitting events Multi-resolution Optical Flow and Reynold stress Conclusions
Conclusion Both natural and externally induced flows have similar impact on breaking and tilting eddies Tilting and breaking depends on shear rate and shearing rate needs to be larger than some limit to break turbulent eddies, as confirmed in both ohmic and biasing Experiments. The multi-resolution optical flow approach has been implemented to reconstruct the velocity vector field. Before biasing the generation of Reynold stress due to symmetry breaking (tilting) is helpful to induce Low-Frequency Zonal Flows, which could be beneficial to reach the biasing H-mode.
Supplement
The impact of naturally sheared flow Tilting and breaking eddies under the natural shear flow dV E r × B -1 E r x B flow shear rate ω s = ⋅ l cr l cθ dr ω D = 1 / τ c = 1.0 ⋅ 10 5 s − 1 Natural scattering rate
Supplement
Supplement Splitting collection
Supplement
Supplement before bias. during bias. shear shear layer layer shear layer
Biasing experiment ( splitting events )
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