Measurements of Core Electron Temperature Fluctuations in DIII-D with Comparisons to Density Fluctuations and Nonlinear GYRO Simulations

Transcription

1 Measurements of Core Electron Temperature Fluctuations in DIII-D with Comparisons to Density Fluctuations and Nonlinear GYRO Simulations A.E. White,a) L. Schmitz,a) G.R. McKee,b) C. Holland,c) W.A. Peebles,a) T.A. Carter,a) M.W. Shafer,b) M.E. Austin,d) K.H. Burrell,e) J. Candy,e) J.C. DeBoo,e) E.J. Doyle,a) M.A. Makowski,f) R. Prater,e) T.L. Rhodes,a) G.M. Staebler,e) G.R. Tynan,c) R.E. Waltz,e) and G. Wanga) a)university of California-Los Angeles, Los Angeles, California, USA b)university of Wisconsin-Madison, Madison, Wisconsin, USA c)university of California-San Diego, La Jolla, California, USA d)university of Texas, Austin, Texas, USA e)general Atomics, P.O. Box 868, San Diego, California, USA f)lawrence Livermore National Laboratory, Livermore, California, USA Presented at: GPS-TTBP Meeting Feb 9-Mar 1 8 UCSD

2 Correlation Electron Cyclotron Emission (CECE) diagnostic measures local, low-k electron temperature fluctuations nd Harmonic ECE layer Flat mirror Mixer IF Filters f = 1 MHz!! IF if f1 Video Amplifiers f =. MHz vid VID f1 f Parabolic mirror Shot ms EFIT6 Lens LO z +. cm - 6. cm f.7 Thermal noise in single ECE signal f1 f CECE Midplane BES ( T e /T e ) f V ID f IF Standard cross-correlation techniques reduce the thermal noise, RMS amplitude and spectrum are measured Gaussian optics and narrow IF filters provide spatial resolution required for turbulence measurements R

3 Beam Emission Spectroscopy (BES) diagnostic measures local, low-k density fluctuations nd Harmonic ECE layer Flat mirror Lens CECE and BES diagnostics have similar spatial resolution Mixer LO IF Filters B = 1 MHz if f1 f Video Amplifiers B =. MHz vid CECE and BES sample volumes are separated toroidally and vertically, but can measure at same radial location z +. cm.7 f1 f CECE CECE Te/Te k < 1.8cm 1 Shot ms EFIT6-6. cm Midplane R BES BES n/n k < 3cm 1

4 Issues for comparison and validation studies How can CECE measurements be used to study the TEM? T-perp carries information about trapped population Conditions when X-mode ECE measures T-perp, CECE measures T- perp fluctuations. Can this be tested? Is there a clear difference predicted for n-tilde/te-tilde for ITG vs TEM? Can ne-tilde and Te-tilde amplitudes/spectra alone give valuable information for validation studies? Phase measurements <ne-tilde Te-tilde>? Oblique CECE? O-mode CECE? Pick out differences between T-par and T- perp? O-mode ECH vs X-mode ECH? Can multi-field fluctuation measurements be used to help define metrics and methods of validation beyond comparison?

5 Relative fluctuation levels n /n n /n e e T /T e e T /T e Exp. GYRO Exp. e GYRO Normalized radius

6 Experiment using local ECH to change local Experimental Set-up Te gradient and turbulence drives 1..8 Ip (MA) Ip (MA) NB only NB + ECH Baseline discharge with beam heating only Pinj (MW) Pinj (MW) Te (kev), =.7 Te (kev), =.7!! Te (kev/m), =.7 Te (kev/m), =.7.6 MW ECH 1 1 Time (ms) 1 Ip = 1 MA, BT =. T,. MW of co-injected beam power Compare to discharge with additional EC heating at.17 With ECH: Chi, Q increase and TGLF indicates increase in TEM growth rate Times used in analysis 1-17 ms

7 Ti (kev) , 16 ms 199, 16 ms Normalized! L Ti (m) Normalized! R/LTi - decrease (all three radii) R/LTe - increase rho.6 R/Lne - increase rho.6 Te (kev) 3 199, 16 ms 199, 16 ms L Te (m) Normalized! Normalized! Zeff - increase (all three radii) n e (1 19 m -3 ) L ne (m) eta_i - decrease (all three radii) Te/Ti - increase (all three radii) shear - decrease (inner radii) Normalized! Normalized! 1.

8 heat flux (watts/cm ) ECH experimental results : Electron flux increases ( 3x) at all radii with ECH. Ion heat flux increases ( 3%) at all radii heat flux (watts/cm ) q 16 ms 199 elec q 16 ms 199 elec 1 8 q 16 ms 199 ion q 16 ms 199 ion

9 E r (kv/m) ECH experimental results rho =.7 : Temperature fluctuation amplitude increases -- density fluctuation amplitude stays the same ( ms ms Beam only Beam + ECH Normalized radius! ECH at! = ) Power Spectra 1 khz NB only NB + ECH 1. % : - khz (a) 1. % : - khz ( T /T e e 1. % : - khz (b) 1. % : - khz ( 1 3 Frequency (khz)

10 Relative fluctuation levels ECH experimental results : Temperature fluctuation amplitude increases at three radial locations. Largest increase at =. ( NB only NB + ECH NB only T /T e e n/n T /T e e n/n NB + ECH Normalized radius -7-1 ) e Power Spectra 1 khz ( T /T e ms ! =. 3.8 %.3 % Frequency (khz) 1999 (a)! =.7 1. % 1. % (b)! =.6 1. %.6 % (b)

11 Linear stability results : ITG growth rate decreases at relevant scales, TEM growth rate increases at relevant scales.6. gamma_ion ktheta_rhos =.3 ECH 199 no ECH gamma_electron ktheta_rhos =.3 ECH 199 no ECH 199 Growth rate of ion mode at fixed decreases at all radii. k θ ρ s =.3 Growth rate of electron mode at fixed k θ ρ s =.3 increases across the radius, but largest increase at rho

12 TGLF results : growth rate of most unstable mode largely unchanged at ktheta_rhos =.3, =.,.6, ms γ mks (.,.6,.7) = (.,.7,.8) 1 rad/sec k θ ρ s ms γ mks (.,.6,.7) = (.,.7,.9) 1 rad/sec k θ ρ s

13 Linear stability results : ITG growth rate decreases at relevant scales, TEM growth rate increases at relevant scales 199 no ECH 199 ECH γ ion γ ion k θ ρ s k θ ρ s γ electron γ electron k θ ρ s k θ ρ s

14 TGLF results : growth rate of most unstable mode largely unchanged for k_theta rho_s <.3 at rho =.7, but TEM increases, ITG decreases # (rad/sec) # (rad/sec) # (rad/sec) rho =.7 Growth rate of most unstable mode largely unchanged with and without ECH TEM growth rate increases at long wavelengths with ECH ITG growth rate decreases at long wavelengths with ECH! k s "

15 Temperature fluctuations are measured in L-mode, H-mode and Ohmic plasmas in a single discharge Ip = 1 MA, BT =.1 T,. -1 MW injected beam power, upper single null Measure Te/Te in Early L-mode 7-9 ms Stationary L-mode 1-16 ms ELM-free H-mode ms Ohmic ms (a) (b) (c) (d) Time (ms) V ExB (km/s) P (MW) inj Edge D-! light (a.. u.) T i T e (kev) "=.73 =.7 n chord (1 m ) e 19-3.

16 Doppler shift broadens spectrum and Te/Te is reduced in H-mode Typical cross-power spectra of Te/Te at =.7 Spectrum broadens and narrows in response to Doppler shifts due to changing ExB rotation H-mode temperature fluctuations are below sensitivity limit (.%, 3 ms) Corresponds to factor of 3 reduction in normalized fluctuation level Normalized fluctuation levels in Ohmic (1%) are lower than L-mode (1.%) at same radius Cross-power (T/T) ms 1 T/T! 1. % 1 3 Frequency (khz) -7 x1 khz -1 Early L-mode L-mode 7-9 ms T/T! 1. % 1891 =.7 Stationary L-mode 1-16 ms! T/T 1. % H-mode ELM-free H-mode ms T/T <.% Ohmic Ohmic VExB =.1 km/sec VExB = 7.1 km/sec VExB = 6. km/sec VExB =. km/sec