Variation of Turbulence and Transport with the Te/Ti Ratio in H-Mode Plasmas

Variation of Turbulence and Transport with the Te/Ti Ratio in H-Mode Plasmas by G.R. McKee with C.H. Holland, C.C. Petty, H. Reimerdes,5, T.R. Rhodes6,L. Schmitz6, S. Smith, I.U. Uzun-Kaymak, G. Wang6, A.E. White7, Z. Yan University of Wisconsin-Madison of California -San Diego General Atomics Columbia University 5 University of California - Los Angeles 6CRPP-EPFL, Lausanne 7Massachusetts Institute of Technology University Presented at the 5nd Annual Meeting of the APS Division of Plasma Physics Chicago, Illinois November 8-, GR McKee/APS/November 96-/GRM/rs 96-/GRM/rs

Overview Increasing Te/Ti influences transport in L and H-mode plasmas Reduces density Reduces rotation Reduces τe Current experiments typically operate with Ti > Te Reactors/ITER will have Te~Ti Previous studies in related L-mode experiments find that Transport increases with T e /T i, but; Long-wavelength density fluctuations relatively constant T e fluctuations increase (CECE, A. White, PoP 9) Turbulence increases significantly with Te/TI in H-mode plasmas Contrasts with behavior in L-mode discharges These H-mode plasmas exhibit two core fluctuation modes Performed as part of the Transport Model Validation Task Force Future work will compare turbulence and transport with simulations GR McKee/APS/November 96-/GRM/rs

Turbulence and Transport Response to Te/Ti Investigated in Hybrid H-mode Plasmas Hybrid H-mode Plasmas Long, quasi-steady (.5 s) Sawtooth-free High-performance Discharge Parameters Ip =.6 MA BT =.9 T q95=5.9 ITER Shape (ISS) PCS Feedback control Density TI, Rotation (CER) Beam Power Density Te() Higher Te/Ti (ECH) Lower Te/Ti (No ECH) Ti() Time-Window of Interest VTOR() βn ECH/RF increases Te/Ti. MW ECH/.8 MW RF 5% increase in Te % drop in τe ECH Power τe Time (ms) GR McKee/APS/November 96-/GRM/rs

ECH Increases Te: Impacts all Profiles PCS feedback of density and beams employed to minimize variation ~5% increase in Te T e (kev) 5 ECH No ECH T I (kev) 7 6 5. 5...6.8..x 5....6.8. Density ( 9 m - ) V TOR (km/s).5..5.....6.8 Minor Radius (r/a).. -.5....6 Minor Radius (r/a).8. GR McKee/APS/November 96-/GRM/rs

Thermal Transport Increases Significantly at Higher Te/Ti Thermal Diffusivity Profiles 8 ECH No ECH e (m /s) 6 i (m /s) 8 6....6 Minor Radius (r/a).8.....6 Minor Radius (r/a).8. ONETWO Transport Analysis GR McKee/APS/November 96-/GRM/rs

Turbulence Measured with Beam Emission Spectroscopy Long-wavelength density fluctuation data acquired with highsensitivity 8x8 BES D array Highly repeatable discharges allow for diagnostic scans (r, k) k ρi < cm - Long discharges (.5 s steady phase) allow for ensemble averaging to discern low amplitudes (ñ/n<.5%) fluctuation characteristics Fluctuation data also acquired with CECE, DBS-5, DBS-8 GR McKee/APS/November 96-/GRM/rs

Long-Wavelength Density Turbulence Increases with Te/Ti Qualitatively similar behavior observed across radius Spectra (V /V DC /khz) Spectra (V /V DC /khz).x -8...8.6.. x -8. 5 6(ECH)/9(NoECH),ST:8 NP/NB:5/5,OS/DC;ELM,ET:. 5 High Te/Ti (.%) Low Te/Ti (.9%) r/a=.5 5 High Te/Ti (.7%) Low Te/Ti (.5%) r/a=.5 Spectra (V /V DC /khz) Spectra (V /V DC /khz) x -8 x -8 5 5(ECH)/(NoECH),ST:8 NP/NB:5/5,OS/DC;ELM,ET:. 5 High Te/Ti (.6%) Low Te/Ti (.%) r/a=.5 5 High Te/Ti (.) Low Te/Ti (.5) r/a=.7 5 (ECH)/(NoECH),ST:8 NP/NB:5/5,OS/DC;ELM,ET:. 5 5 5 (ECH)/(NoECH),ST:8 NP/NB:5/5,OS/DC;ELM,ET:. 5 5 GR McKee/APS/November 96-/GRM/rs

H-Mode Core Fluctuation Spectra Exhibit Two Non-ECH heated discharge has frequency regions with distinct spectral and phase shift (propagation velocity) characteristics Likely reflects two different modes/instabilities ECH-heated discharge exhibits single mode Poloidally-separated channels required to distinguish modes Higher frequency mode has lower amplitude; longer correlation length Cross Power (V /V DC /khz) Cross Phase (rad) 8x -6 6 5 - - - 5 ΔZ=. cm,, CH /,/8 ST:8, NP:5,NB:5,OS/DC,ELM/ET=. 5 5 High Te/Ti (ECH) Low Te/Ti (No ECH) 5 5 x -6 GR McKee/APS/November 8 6 5 - - - 5 ΔZ=7.8 cm 5 5 5 5 96-/GRM/rs

TGLF Calculations Show Lower Growth Rates at Higher Te/TI TGLF analysis with measured n, T, rotation profiles Mixture of ion modes at lower-k, electron modes at higher-k Higher Te/Ti discharges show significantly higher growth rates at higher k (.6 < k ρs <) ρ=.6 8x - lin (a/c s ) 6 Higher T e /T I (ECH) Lower T e /T I (No ECH)... k s.6.8 See C. Holland, NI.5, Wed. GR McKee/APS/November 96-/GRM/rs

L-Mode and H-mode (Hybrid) Discharges Exhibit Different Turbulence Response to Te/Ti Variation L-mode: long-wavelength density fluctuations exhibit small change in magnitude with Te/Ti Spectral shape change reflects local changes in ExB Doppler shift Te-fluctuations increase (CECE) H-mode: long-wavelength density fluctuations increase measurably in magnitude with Te/Ti Spectra (V /V DC /khz) x -8 H-mode (Hybrid) High Te/Ti (.7%) Low Te/Ti (.5%) r/a=.5 Power Spectra(a.u.) 5x -8 L-mode High Te/Ti (.%) Low Te/Ti (.7%) r/a=.56 5 (ECH)/(NoECH),ST:8 NP/NB:5/5,OS/DC;ELM,ET:. 5 5 vθ(low Te/Ti) = 8. km/s vθ(high Te/Ti) = 6.9 km/s 5 GR McKee/APS/November 96-/GRM/rs

Fluctuation Variation with Te/Ti Different for L-Mode & H-mode Hybrid H-mode discharges exhibit a clear -% increase in low-k density fluctuation amplitude with increasing Te/Ti L-mode plasmas exhibit small, if any, increase with Te/Ti Consistent with previous and recent experiments L-mode Fluctuation Amplitude (%).5..5..5.. H-Mode...5.6.7 Minor Radius (r/a).8 Fluctuation Ampliutde (a.u.).5......55.6 L-Mode High Te/Ti (ECH) Low Te/Ti (No ECH) 6,67(ECH),6,68(No ECH), 5/, ST: 6(E)/, r/a:6-,-, OS/DC.65.7 Minor Radius ( ).75.8 T. Rhodes, IAEA- GR McKee/APS/November 96-/GRM/rs

Summary Turbulence and transport response to variation in Te/Ti examined in Hybrid H-mode plasmas Te/Ti <, increased by 5% via. MW ECH + RF heating % reduction in τe Low-k density turbulence increases by 5-% with Te/Ti ~ Related L-mode experiments show much small increase in ñ/n with Te/Ti, but Te/Te increases significantly Core H-mode turbulence exhibits signature of two distinct turbulence bands at different (but overlapping) frequency/ wavenumber ranges Mode structure varies appreciably with Te/Ti Initial TGLF growth rate calculations do not appear consistent But: higher k growth rates increase significantly at higher Te/TI Future analysis with nonlinear simulations (e.g., GYRO) for model validation studies GR McKee/APS/November 96-/GRM/rs