The experimental investigation on the role of E x B The experimental - - PowerPoint PPT Presentation

• I. Shesterikov1, Y. Xu1, С. Hidalgo2, S. Jachmich1, P. Dumortier1, M. Berte1,
• M. Vergote1, M. Van Schoor1, G. Van Oost3 and the TEXTOR team

The experimental investigation on the role of E x B flow shear in tilting and breaking turbulent eddies The experimental investigation on the role of E x B flow shear in tilting and breaking turbulent eddies

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

Vedia Vidia

The impact of naturally sheared flow

LCFS Vidia Vedia

The impact of naturally sheared flow

5% - Tilt Only 30% - Tilt and Split We had analyzed 4959 images in 19 discharges Among them

• I. Shesterikov, Y. Xu et al., Nuclear Fusion 52, 042004 (2012).

Directly observed for the first time

The impact of naturally sheared flow

Tilting and breaking eddies under the natural shear flow

Er x B flow shear rate

ωD=1/τ c=1.0⋅105 s−1

Natural scattering rate

ωs=1.2⋅10

5 s −1

ωs=2.6⋅10

5 s −1

Tilt Tilt and Split

ωs ωD =1.2

Tilt Tilt and Split

ωs ωD =2.6

• 1

ωs= dV Er×B dr ⋅lcrlcθ

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

H-mode transition

Biasing experiment

H-mode transition

Biasing experiment

Ohmic Biasing H-mode

Biasing experiment

GPI Frame 2D Fourier Transform

Biasing experiment

Ohmic Biasing

No preferential

• rientation

tg (φ )= k θ kr

Preferential

• rientation

Biasing experiment (2D Fourier Transformation)

Ohmic Biasing H-mode

Eddy № 25 Eddy № 26 Eddy № 27

Z [cm]

Biasing experiment (Directional analysis)

Ψ M (x,y,θ )=exp (ik 0 ( x⋅ cos (θ )+y⋅sin (θ )))⋅exp(− 1 2 √x

2+y 2)

W (a,b,s,θ )=s

−1∬Ψ M(

x−a s , y−b s ,θ) I ( x,y )dxdy

2D Morlet wavelet 2D Wavelet Transform

Biasing experiment (Directional analysis)

Biasing experiment (Directional analysis)

No preferential

• rientation

preferential orientation No preferential

• rientation

Ohmic Biasing H-mode

Biasing experiment (splitting events)

Biasing H-mode Ohmic

ε b

2(V x ,V y)=∬[

∂ E ∂ t + ∂ E ∂ x⋅V x + ∂ E ∂ y⋅V y]

2

dxdy

∣∇ V x∣2=( ∂V x ∂ x )

2

+( ∂ V x ∂ y )

2

∣∇ V y∣2=( ∂V y ∂ x )

2

+( ∂V y ∂ y )

2

εc

2(V x,V y)=∬(∣∇ V x∣ 2)+(∣∇ V y∣2)dxdy

Biasing experiment (optical Flow)

Typical video of Vector Field

Biasing experiment (Reynold Stress)

<VrVθ> <VrVθ>

• Y. Xu et al., PoP 16, 110704 (2009).

Biasing experiment (Reynold Stress)

Biasing experiment (Reynold Stress)

b2(f 1,f 2)

Ohmic Biasing

b2(f 1,f 2)

Flow shear Tilting of eddies Symmetry breaking Generation of Reynold stress Low frequency Zonal Flow

Prior L-H transition

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

Tilting and breaking eddies under the natural shear flow

ωs= dV Er×B dr ⋅lcrlcθ

Er x B flow shear rate Natural scattering rate

The impact of naturally sheared flow

• 1

ωD=1/τ c=1.0⋅105 s−1

Supplement

Supplement

Splitting collection

Supplement

Supplement

shear layer shear layer shear layer

before bias. during bias.

Biasing experiment (splitting events)