1

HL-2A

Spatial and spectral characteristics of large scale coherent structures in edge turbulent plasmas of HL-2A

tokamak J. Q. Dong1,2, K.J. Zhao1, J. Cheng1, L.W. Yan1, W. Y. Hong1,

Z. H. Huang1, D. F. Kong3, Q. W. Yang1, X. T. Ding1, X. R. Duan1, HL-2A Team

1) Southwestern Institute of Physics, Chengdu, China2) IFTS, Zhejiang University, Hangzhou, China3) University of Science and Technology of China, Hefei, China

International West Lake Symposium on Fusion Plasma PhysicsHangzhou, China, May 25-27, 2011

2

HL-2A

Outline 1. Introduction2. Discharge parameters and probe setup 3. Experimental results4. Summary

3

HL-2A1. Introduction • Formation of large scale coherent structures (LSCS) such as zo

nal flows (ZFs, including LFZF and GAM) and blobs/filaments is universal in turbulent plasmas.

• ZFs are defined as azimuthally symmetric radial electric field fluctuations with radial meso-scale.

• Blobs (filaments) are identified as asymmetric LSCSs stretching along magnetic field lines.

• Experimental identification of the LSCS is important to understand transport and confinement in fusion plasmas.

• Formation mechanism of the LSCS is of fundamental scientific interest and under intensive investigation.

• Spatial and spectral characteristics and generation mechanism of the LSCS are studied in the edge of HL-2A tokamak plasmas.

4

HL-2A

•R: 1.65 m•a: 0.40 m•Bt: 1.9/2.7T•Configuration: Limiter, LSN divertor•Ip: 168/450 kA•ne: 1.9/8 x 1019m-3 •Edge safety factor q95=3.5-6.5

Auxiliary heating: ECRH/ECCD: 3 MW (4/68 GHz/500 kW/1 s) modulation: 10~30 Hz; 10~100 % NBI (tangential): 1.0 MW LHCD: 1 MW (2/2.45 GHz/500 kW/1 s)

Fueling system (H2/D2):

Gas puffing (LFS, HFS, divertor)

Pellet injection (LFS, HFS)

SMBI (LFS,HFS) LFS: f =1~60 Hz, pulse duration > 0.5 ms, gas pressure < 3 MPa

2. Discharge parameters and probe setup

5

HL-2A

3D Langmuir probe arrays for ZF

2. Experiment arrangement

PP

RP

TSLP

• Sampling rate = 1 MHz• Spatial resolution= 4mm• Diameter of tips is 1.5 mm. • Height of tips is 3 mm.

6

HL-2A

The combination of poloidal 10-tip (A) and radial 8-tip (B) probe arrays with a toroidal separation of 60 degrees (210 cm).

• Array A is located d1= 2.1 cm blow the mid-plane, • Array B is located d2=5.2 cm above the mid-plane.

Sampling rate = 1 MHzSpatial resolution= 4mm

3D Langmuir probe arrays for blob

Diameter of tips is 1.5 mm. Height of tips is 3 mm.

7

HL-2A3.1 Experimental results for zonal flow

The poloidal and toroidal symmetries, i.e, m=0,n=0 were measured, simultaneously, for LFZF and GAM.

AT

k (cm-1)

f(kH

z)

-0.6 -0.3 0 0.3 0.60

10

20

30

k(cm-1)

f(kH

z)

-0.01 0 0.010

10

20

30

GAM

GAM

LFZF

S(k,f) S(k,f)

(a) (b)(e) (f ) GAM

LFZF

Coexistence of intensive LFZFs and GAMs

8

HL-2AFinite radial wave number

• Kr=0.6cm-1, Δkr =3.7cm-1 for the LFZF• Kr=3.8cm-1, Δkr =3.8cm-1 for the GAM

(a) Radial wave frequency-vector spectrum of potential fluctuations,

(b) radial wave vector spectra for the LFZF and GAM,

c) Radial coherency spectrum.

9

HL-2ARadial variation of ZF power spectra

• Moving from the last close flux surface inwards, the intensity of GAM first goes up, then decreases.

• The intensity of LFZF increases inwards

• The intensities of LFZF and GAM both increase with ECRH power

440 460 480 500 520 540 560 580 600-200

-100

0

time (ms)

f(V

)

OH ECRH

r=-3.2cm

10

HL-2ARadial distribution of power partition

GAM dominantCoexistence• The LFZF (a) and GAM (b)

power partition as a function of radial position in OH, ECRH discharges

• LFZF+GAM (c), AT (d) power partition as a function of radial position in OH and ECRH plasmas.

• GAM dominating near LCFS, but LFZF & GAM are nearly equal in the inner region

• LFZF+GAM power partition has a maximum at r~-1.2 cm and is lower in ECRH plasmas.

11

HL-2A

Radial profiles of edge plasma shear flows, Reynolds stress and fluctuations

• Rs=<VrVθ>

• Rs’=(VrVθ)’

12

HL-2A

The waveforms of the radial electric field fluctuation of GAM, Reynolds stress and its gradient in GAM frequency band.

Turbulence modulation by shear flows

2 2| | 2 2| |

(a) The shearing rate of LFZF and

in LFZF frequency band,

(b) the shearing rate of GAM and

in GAM frequency band.2 2| |

2 2| |

13

HL-2A

3.2 Experimental Results for blobs

The contour of maximum coherence, the maximum coherence and average wave vector measured in SOL (a)-(c) and edge plasmas (d)-(f).

r (

mm

)

81624

0.50.60.70.8

max

.

32241680

210

-1-2

d (mm)

k l (10-2

cm-1

)

0.50.60.70.8

max

.

32241680

210

-1-2-3

d(mm)

k l (10-2

cm-1

)

r

(mm

)

-20-12

-4

0.20.40.60.8

0.20.40.60.8

(b)

(a) (d)

(e)

(f)(c)

EdgeSOL

}])({[}])({[/]})(][)({[)( 22 ytyExtxEytyxtxExy

Coherence

14

HL-2AGeneration in edge

Two-dimensional images of conditional average of the floating potentials across the LCFS at six times of 2 s interval.

Polo

idal

(mm

)

-10 0 100

10

20

30

-10 0 100

10

20

30

-10 0 100

10

20

30

r(mm)

Polo

idal

(mm

)

-10 0 100

10

20

30

r(mm)-10 0 10

0

10

20

30

r(mm)-10 0 10

0

10

20

30

(b) (c)

(e) (f)(d)

(a)

-6

-4

-2

0

2

Er (

kv.m

-1)

-10 0 10 20-4-2024

r (mm)

E (

105s-1

)

(a)

(b)

Profiles of Er and E= V/r

15

HL-2A

Shearing time: [H. Biglari, et al, Phys. Fluids B2, 1, 1990],

In the shearing region，Lr1.5 cm, k2.0 cm-

1, V/r=E=2.8×105s-1, sh7s.

1)2

(

rVLk r

sh

Polo

idal

(mm

)

-10 0 100

10

20

30

-10 0 100

10

20

30

-10 0 100

10

20

30

r(mm)

Polo

idal

(mm

)

-10 0 100

10

20

30

r(mm)-10 0 10

0

10

20

30

r(mm)-10 0 10

0

10

20

30

(b) (c)

(e) (f)(d)

(a)

Generation in edge

16

HL-2AEvolution of the shearing rate profile

r (mm)

(

s)

-10 -5 0 5 10 15 20

-4

-2

0

2

4

6

-0.50.51.52.5

E (105s-1)

Cross-conditional average

1) The peak of the shearing rate appears in the region -10 mm<r<-5 mm ;

2) The peak of the shearing rate starts to increase from =0 and reaches maximum in the interval 2<<4s ;

17

HL-2A

Two-dimensional images of conditional average of the floating

potentials in the SOL at six times of 5 s interval.

Propagation in SOL

18

HL-2A4. Summary The spatial and spectral structures of multiple shear flow pop

ulations, the shear flow-turbulence dynamics are investigated at the edge plasmas of HL-2A tokamak with ohmic and electron cyclotron resonance heating.

The LFZF and GAM power tends to coexist in the inner region and GAM dominates near the LCFS.

The Reynolds stress of the ambient turbulence is found to be well correlated with the mean flow, LFZF and GAM, suggesting that multiple shear flows are driven by nonlinear interaction with turbulence via the stress.

The analysis of shear flow-turbulence interaction demonstrates that the edge turbulence is modulated by all the multiple shear flows.

19

HL-2A

The characteristics, generation mechanism and propagation of blobs are investigated in the edge and scrape-off layer plasma of HL-2A tokamak for the first time.

The spontaneous EB sheared flows are identified responsible for the generation of the blobs.

20

HL-2A

Thank you for your attention!