Multi-scale turbulence, electron transport, and Zonal Flows in DIII-D L. Schmitz 1 with C. Holland 2 , T.L. Rhodes 1 , G. Wang 1 , J.C. Hillesheim 1 , A.E. White 3 , W. A. Peebles 1 , J. DeBoo 4 , G.R. McKee 5 , J. DeGrassie 4, L. Zeng 1 , E. J. Doyle 1 , C.C. Petty 4 , J. Kinsey 4 , G. Staebler 4 , K. H. Burrell 4 , M.E. Austin 6 , and the DIII-D Team 4 1 University of California, Los Angeles 2 University of California, San Diego 3 Massachussets Institute of Technology 4 General Atomics, San Diego 5 University of Wisconsin, Madison 6 University of Texas at Austin Kinetic Scale Turbulence in Laboratory and Space Plasmas Workshop Cambridge, July 19-23, 2010
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Multi-scale turbulence, electron transport, and Zonal ... · for studying electron transport. • DBS data indicate intermediate-scale turbulence regulation by Zonal Flows in an electron
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Multi-scale turbulence, electron transport,and Zonal Flows in DIII-D
L. Schmitz1
withC. Holland2, T.L. Rhodes1, G. Wang1, J.C.Hillesheim1, A.E. White3, W. A. Peebles1,J. DeBoo4, G.R. McKee5, J. DeGrassie4,
L. Zeng1, E. J. Doyle1, C.C. Petty4,J. Kinsey4, G. Staebler4, K. H. Burrell4,M.E. Austin6, and the DIII-D Team4
1 University of California, Los Angeles2 University of California, San Diego3 Massachussets Institute of Technology4 General Atomics, San Diego5 University of Wisconsin, Madison6 University of Texas at Austin
Kinetic Scale Turbulence in Laboratory and Space Plasmas Workshop Cambridge, July 19-23, 2010
Why is intermediate/small-scale turbulence important?
• Understanding electron thermal transport in H-mode plasmas iscritical for next-step burning plasma experiments such as ITER(α-particle heating).
• Electron transport is driven by multi-scale phenomena.Local measurements of intermediate/smaller-scale densityfluctuations (kρe ≤ 0.2) have become available (DopplerBackscattering, DBS).
• Gyrokinetic code results (GENE, GYRO) predict thatintermediate/small-scale turbulence may be important
(or possibly dominant) in H-Mode.
• Local multi-scale turbulence measurements providecritical tests and validation of Gyrokinetic predictive codes.
Outline
• Introduction
• Core turbulence behavior across the L-H transition
• Multi-scale turbulence in high temperature,low collisionality H-mode plasmas:
- radial profiles- wavenumber spectra, linear stability
- GYRO simulations
• ECH-Heated QH-modes: Te/Ti ~1
• Zonal Flows and intermediate-scale turbulence
Cyclone ITG/TEM/ETGsimulation: 50% of electronheat flux driven for kθrs ≥ 0.5.
Core electron thermal diffusivity decreases within~10 ms of H-mode edge barrier formation
Electron heat diffusivity(from TRANSP) decreasesrapidly across minor radius
L-H transition
At the L-H transition, core fluctuations (0.4 ≤ r/a ≤ 0.8) arereduced across a range of wavenumbers
Doppler Backscattering, r/a=0.4~
Moderate reduction before L-Htransition due to increasing E×Bshear; ñ drops at transition within~5-10 ms.
CECE (Te/Te)*, BES (ñ/n), r/a=0.7
L H
*L. Schmitz, A.E. White etal., Phys. Rev. Lett. 100(2008).
L H
The E×B shearing rate exceeds the linear growth ratein the ITG/TEM range in the core plasma in H-mode
L H
Linear growth rate γl is calculated byTGLF. The radial electric field/shearin the core is dominated by toroidalrotation (Er ~ vφ × Bθ). Fluctuationsuppression expected for k⊥ρs ≤ 4in H-mode (r/a=0.4).
Only ETG expected unstablefor r/a ~0.4
DBS
DBS
Electron temperature and density profiles and E×B shearingrate in L- and H-Mode, #131912
H-Mode (1100 ms): strongshear in the core plasma(r/a <0.7) in addition to thepedestal regionLow collisionality νe
*(0.4)~0.04
Radial Electric Field
Waltz-MillerShearing Rate
L-Mode (875ms) H-Mode (1100 ms)
L-Mode H-Mode
Radial profile of Density Fluctuations in L and H-Mode
Both ITG-scale andIntermediate-scalefluctuations are substantiallyreduced in H-mode acrossthe core plasma.
ñ/n is reduced bymore than an order ofmagnitude for r/a < 0.45
Very low H-modeintermediate-kturbulence for r/a <0.45
In H-mode, core fluctuations are reducedin the wavenumber range where α<ωExB> > γl
Exponentialspectra foundin L-Mode:
ñ/n ~ e-β(kρs)
with β =1.5…1.7
TGLF growthrate of most unstable mode
αEωExBa/cs is the normalized shear quench rate
Initial multi-scale GYRO calculations indicate importanceof ETG range (kθρs > 3) for electron thermal transport
Spectrum of potential fluctuations (outboard midplane)
Electron transport spectrum
~kρs-6
~kρs-3.5
Electron Heat flux almost entirely driven by modeswith kθρs > 2
Fixed gradient simulation; Qe GYRO = 0.28 Qe, exp
r/a=0.6
2-D wavenumber spectrum (kr/kθ asymmetry)
Outboard midplane reconstruction (GYRO)
r/a=0.6
DBS measurement
Measured DBS spectralindex is increasedcompared to indexaveraged over <kr>
Achieved Te/Ti > 1 and Te > 10 keV in ECH-assistedQH-mode plasma
Phase velocity is neglected(vph < 0.05 vExB from TGLF, Vt ~ vExB)
1 cm
Localized Zonal Flows are observed near the q=2surface
ZMF (zero-meanfrequency) and lowfrequency Zonal Flowsare observed near theq = 2 surface (r/a ~ 0.5)
A 3/2 tearing modegrows at 1190 ms and istransiently observed atthe same radius. Anisland forms at 1230 m(observed on ECEdata), collapsing theshear layer.
L-mode plasma,co-injected 7 MW
GAM
Flow velocity spectrum fromDoppler Backscattering
1 km/s
0.1km/sZonal Flows
r/a ~0.5r/a~0.5
Intermediate-scale fluctuations are reduced in local ZFshear layer near the q=2 surface
E×B shear reversesacross q=2 surface(measured by DBS)
Barriercollapses
ExB flow shear is anti-correlated with intermediate-scaledensity fluctuation amplitude
• r/a~0.48
• Probedk⊥~6 cm-1
k⊥ρs∼3
First experimental evidence of Zonal Flowinteraction with Intermediate scale turbulence
Anti-correlation is consistent withtheoretical expectations.
1200 ms
Anti-correlation is most pronounced in regions ofhigh shear
Turbulence velocity (DBS)
1200 ms
Summary
• Core electron transport and ITG/intermediate scale core turbulenceare substantially reduced across the L-H transition in low-collisionalityH-mode plasmas.
• Wavenumber spectra (measured by Doppler Backscattering)and TGLF/GYRO simulations indicate that core turbulence reductionis consistent with E×B shear.
• Initial GYRO multi-scale modeling results indicate dominance of high-kturbulence in the core. Fixed-flux runs are in preparation to allowquantitative comparisons to experimentally measured densityfluctuation wavenumber spectra.
• Te/Ti ~ 1 achieved with ECH; reduced ExB shear: interesting regimefor studying electron transport.
• DBS data indicate intermediate-scale turbulence regulation by ZonalFlows in an electron ITB near the q=2 rational surface (L-Mode).