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

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

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

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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