Rapid changes of turbulence propagation direction in the edge of

Transcription

1 Rapid changes of turbulence propagation direction in the edge of I. Cziegler, J. L. Terry MIT Plasma Science and Fusion Center APS Division of Plasma Physics Dallas TX, November 8

2 Motivations for edge/sol turbulence studies Both L- and H-mode plasma regimes exhibit strong edge and scrape-off-layer turbulence in most laboratory discharges Our present understanding of this turbulence is insufficient to explain or predict major characteristics of these plasmas The turbulence of the edge region is often very different from that of the SOL the dynamics of these differences are of high interest for an insight to blob generation The edge flow shear region is believed to be very important in transport and confinement

3 Gas-Puff-Imaging Setup Side view z R B array views 3 mm Top view

4 Background earlier experiments show a clear radial structure In order to characterize the radial profile of the turbulence, the separatrix was swept across the vertical viewing array ρ = 8 mm Frequency (khz) ion ρ stands for distance into SOL at midplane ρ = mm el ion ρ = 9 mm el ion el

5 Background earlier experiments show a clear radial structure In order to characterize the radial profile of the turbulence, the separatrix was swept across the vertical viewing array ρ stands for distance into SOL at midplane Integration time τ ρ = 8 mm ave = 3ms ρ = mm ρ = 9 mm Frequency (khz)

6 e ph v vphi = 1.7 km/s 15 5 =.9 km/s Distance into SOL at Midplane (mm) separatrix Fitted velocity (km/s) Comparison to probe measurements shows important differences [1] B. LaBombard et al., JNM 313, 995 (3) 5 1 Distance into SOL at Midplane (mm) 15 The localization of the shear region and magnitudes match probe measurements

7 e ph v vphi = 1.7 km/s 5 =.9 km/s 5 1 Distance into SOL at Midplane (mm) [1] B. LaBombard et al., JNM 313, 995 (3) The localization of the shear region and magnitudes match probe Distance into SOL at Midplane (mm) measurements Instead of a smooth profile, an abrupt change is observed in the measured velocities, together with a 5 1 mm wide crossover region just outside the separatrix separatrix Fitted velocity (km/s) Comparison to probe measurements shows important differences Propagation velocities are largely invariant in the region!

8 Frequency f (khz)(khz) Integration time decreased to τave = 5µs Frequency f (khz)(khz) Frequency f (khz)(khz) Introducing finer time-resolution reveals rapid velocity flips

9 Integration time decreased to τave = 5µs Frequency f (khz)(khz) Introducing finer time-resolution reveals rapid velocity flips Frequency f (khz)(khz) Separate features different characteristics Frequency f (khz)(khz) Electron feature Ion feature 3. cm 1. cm Correlation length Radial propagation Negligible Considerable Fluctuation distribution Scalable Intermittent Wavelike Blobby

10 Integration time decreased to τave = 5µs Frequency f (khz)(khz) Introducing finer time-resolution reveals rapid velocity flips 1 5 Frequency f (khz)(khz) Frequency f (khz)(khz) A comparison to intermittent brightness fluctuations shows fair alignment 15 Separate features different characteristics Electron feature Ion feature 3. cm 1. cm Correlation length Radial propagation Negligible Considerable Fluctuation distribution Scalable Intermittent Wavelike Blobby

11 The intensity-proportion of the two separate lobes Concentrate to relevant region Frequency (khz)

12 The intensity-proportion of the two separate lobes Concentrate to relevant region Separate the two features in the conditional spectrum Frequency (khz)

13 The intensity-proportion of the two separate lobes Concentrate to relevant region Separate the two features in the conditional spectrum Sum up the coefficients to get relative conditional intensities I el ; I ion Define the normalized proportion of the two lobes as I el I ion = I el I ion Frequency (khz) 15 Iion 1 Iel 5

14 Cross correlation between flips and ejections shows a positive peak t i I, t i i

15 Addressing the issue of the radially invariant poloidal phase velocities: wavelet transform separatrix v (km/s) Combine individual wavelets into a propagating feature with a fixed velocity effectively a multi-correlation over a wide spatial range for every size scale and speed

16 Addressing the issue of the radially invariant poloidal phase velocities: wavelet transform ρ = 1mm 15 ρ = 5mm separatrix v (km/s) Combine individual wavelets into a propagating feature with a fixed velocity effectively a multi-correlation over a wide spatial range for every size scale and speed ρ = 3mm ρ = -mm

17 Addressing the issue of the radially invariant poloidal phase velocities: wavelet transform ρ = 1mm 15 ρ = 5mm separatrix v (km/s) Combine individual wavelets into a propagating feature with a fixed velocity effectively a multi-correlation over a wide spatial range for every size scale and speed ρ = 3mm ρ = -mm

18 Addressing the issue of the radially invariant poloidal phase velocities: wavelet transform ρ = 1mm 15 ρ = 5mm separatrix v (km/s) Combine individual wavelets into a propagating feature with a fixed velocity effectively a multi-correlation over a wide spatial range for every size scale and speed ρ = 3mm ρ = -mm Poloidal wave correlation length Typical blob correlation length

19 Radial propagation and size Exponential (no memory) time distribution with =3±3 sec Peaked at v r =1 km s Radial size is just below the poloidal (blob) =.7 cm 1

20 Summary Measurements showed a clear radial structure with high resolution in both r and k space Two distinct, well defined velocities and a rapid switching in their crossover region Found an indication of correlation between blob ejections and edge kick in the electron diamagnetic drift direction Produced a database of blobs sorted according to size, time and velocity shown more complex statistical features than our single correlation or wavenumber studies Possible to find size-velocity relationship