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An overview of electron thermal transport results from NSTX

Supported by. Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics NYU ORNL PPPL PSI SNL UC Davis UC Irvine UCLA UCSD U Maryland U New Mexico U Rochester U Washington U Wisconsin Culham Sci Ctr Hiroshima U HIST Kyushu Tokai U

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An overview of electron thermal transport results from NSTX

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  1. Supported by Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics NYU ORNL PPPL PSI SNL UC Davis UC Irvine UCLA UCSD U Maryland U New Mexico U Rochester U Washington U Wisconsin Culham Sci Ctr Hiroshima U HIST Kyushu Tokai U Niigata U Tsukuba U U Tokyo Ioffe Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching U Quebec An overview of electron thermal transport results from NSTX E.J. Synakowski, M. Redi, D. Stutman1, K. Tritz1, M.G. Bell, R.E. Bell, W. Dorland2, M. Finkenthal1, K.W. Hill, S.M. Kaye, B.P. LeBlanc, N. Luhmann3, J.E. Menard, H. Park, S. Sabbagh4, D. Smith Princeton Plasma Physics Laboratory [1] Johns Hopkins University [2] University of Maryland, College Park [3] U.C. Davis [4] Columbia University TTF 2005, Napa, California

  2. Electron thermal transport is emerging as a major focus for NSTX transport research • Background • The electron channel typically dominates thermal conduction on NSTX in H and L mode • e can be changed via current profile changes • New capabilities • ∆Te measurement capability reveals rapid responses to edge perturbations • Theory chimes in • GS2, paleoclassical Synakowski, TTF Napa 2005

  3. 250 200 150 100 50 High ne,bt H-mode: Ti, Te,and calculated heating profiles reveal dominance of electron thermal conduction 7 MW H-Mode (bt ≈ 25%, tE ≈ tE,98y2) • Ti > Te although beams predominantly heat electrons • No strong core MHD activity observed. Type-I ELMs at ≈ 50 Hz T (keV) Vf(km/s) ne (1013 cm-3) 8 Ti 6 1.2 Te 4 q 2 0.8 40 80 120 160 R (cm) Vf 0.4 electron heating R0 1 ion heating w/cm-3 40 80 120 160 R (cm) 0 0 0.5 1 r/a Synakowski, TTF Napa 2005

  4. c (m2/s) 100 ce 20 ms variability 10 ciNC 1 ci 0.2 0.4 0.6 0.8 r/a Power balance reveals rapid electron thermal transport with ions near neoclassical predictions 7 MW NB H-Mode • For r/a < 0.4: very small gradients, large calculated heat deposition ==> large values. Also, only weak candidate instabilities identified in this region. 112596a04 (similar plasma as 112596) Synakowski, TTF Napa 2005

  5. Two candidates for driving electron thermal flux in STs emerge in nonlinear GS2 calculations ES m2/s e • ETG simulation yields e ~ 10 m2/s (1/2 radius: gradient region) - dominantly electrostatic • tearing also yields high fluxes. Simulations from MAST (not shown) indicate EM heat flux over ES, e > 10 m2/s - to be carried out for NSTX EM Synakowski, TTF Napa 2005

  6. Electron transport can be reduced in NSTX Ip (MA) 1.0 Fast ramp Slow ramp 0.5 2 MW NB • Investigate magnetic shear effects in low ne, high Te L-Modes • Vary Ip ramp rate, beam onset time to vary magnetic shear • Times t1 and t2 for comparison of magnetic shear effects (no reconnections, ne1 ≈ ne2, Vf1≈ Vf2) <ne> (cm-3) 2 1013 1 1013 2.0 Te0 (keV) 1.0 Vf0 (Km/s) 200 100 t1 t2 0.0 0.1 0.2 0.3 0.4 t (s) Synakowski, TTF Napa 2005

  7. Steep Te,Ti gradients develop in fast ramp case T (keV) Te 1.5 Fast Ramp (t1) Ti 1.0 wf (105 s-1) ne (1013 cm-3) 0.5 2.0 2.0 R0 1.0 1.0 1.5 Slow Ramp (t2) Te Ti 1.0 0 0.5 1 0 0.5 1 r/a r/a 0.5 R0 40 80 120 160 R (cm) • Comparable wf, Ti/Te, collisionality and b (≈8%) Synakowski, TTF Napa 2005

  8. In L mode, transport varies with magnetic shear Fast ramp Slow ramp 4 4 TRANSP q(r) TRANSP q(r) 2 2 USXR q=2 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 c (m2/s) c (m2/s) 100 100 ce ci 10 10 ce 1 1 ci ciNC ciNC TRANSP q(r) 4 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 r/a r/a Synakowski, TTF Napa 2005

  9. Electron and ion barriers are at different radii T (keV) 1.5 Fast ramp (t≈0.21 s) Ti Te 1.0 0.5 R0 R (cm) 40 80 120 160 0.4 0.4 max(s<0) qmin 0.3 0.3 t (s) eITB t (s) 0.2 0.2 iITB 0.1 0.1 0.2 0.4 0.2 0.4 r/a r/a • Electron ITB in region of large negative shear • Ion ITB in region of low magnetic shear (near qmin) Synakowski, TTF Napa 2005

  10. Reduced instability drive in regions of s < 0 Fast ramp Slow ramp 106 106 wExB g,wExB (s-1) wExB 3 3 q q 105 105 2 2 104 104 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 r/a r/a ITG-TEM Redi µ-tearing (kqri <1) ETG • ITG-TEM reduced in iITB region (s ≈ - 0.6) • µ-tearing reduced in eITB region (s ≈ -1.7) - preliminary • ETG reduced or stable in regions of s < 0, s ≈ 0 Synakowski, TTF Napa 2005

  11. 100 10 H mode m2/s 1 100 ce 10 PC ce 1 0.2 0.4 0.6 0.8 r/a From Callen, PRL & UW-CPTC 04-3 A first comparison to paleoclassical theory: undershoots H mode, but intriguing similarity in trends in the L mode core L mode, slow and fast Ip ramp PC theory slow ramp fast ramp slow ramp fast ramp Power balance 0.8 0.2 0.4 0.6 r/a • Collisionless limit of PC theory, no consideration of simple rational q values • In theory, 1/|q'|0.5 dependence plays a large role in the e drop Synakowski, TTF Napa 2005

  12. Type-I ELM impact large on core Te, smaller on ne Te #112581 (7 MW NBI, 1 MA, 4.5 kG) USXR Ha From MPTS (LeBlanc) ne • Thomson Te profile drops after ELM and recovers ~ 17 ms later • Note Te does not change at drop • Density profile little perturbed Synakowski, TTF Napa 2005

  13. 475 480 485 490 495 MPTS t2 keV USXR R (cm) Te(r,t) from SXR shows rapid arrival of edge perturbation in core #112550 MPTS t1 MPTS t2 ELM Te keV • Fast time response inferred from "two color" USXR spectroscopy (Stutman, Tritz, JHU) • Te profile evolves with little change in gradient (‘resiliency’) r=0.2 r=0.4 r=0.6 r=0.8 t (ms) Selectable cutoff energies: - core/edge MHD imaging - ‘two-color’ Te profiles R/LTe from t=480 to t=484 ms R (cm) Synakowski, TTF Napa 2005

  14. Electron thermal transport is emerging as a major NSTX research focus • Electron thermal transport typically dominates thermal conduction on NSTX in H and L mode • e can be changed via the current profile • ∆Te measurement capability reveals rapid responses to edge perturbations • Linear analysis predicts a wide variety of modes. Nonlinear analysis indicates ETG transport can account for fluxes in outer region of H mode. • First cut at paleoclassical - misses on the H mode, captures some aspects of core changes in the L mode cases • High k measurement plans for 2005: unique opportunities Synakowski, TTF Napa 2005

  15. Two regions with different transport characteristics are suggested by cold pulse propagation Time-to-peak (ms) Te at t1 (keV) 2.0 1.5 • cet peak = 1/8 Dr2/Dtpeak (sawtooth model) • ->hundreds m2/s outside r > 0.5 • -> tens of m2/s inside • Opposite trend to cePB • Suggests electron transport strongly driven above critical in the Te region and nearer to threshold where Te flattens 1.0 0.5 r 1000 cet peak cePB ce (m2/s) 100 10 r Synakowski, TTF Napa 2005

  16. mtearing High k scattering range ETG ITG ITG/TEM rs k 0.1 1 10 k (cm-1) 10 0.1 1 100 NSTX electron thermal transport plan takes advantage of some unique plasma characteristics • Anisotropic turbulence + strong toroidal curvature + Bragg condition  Excellent spatial resolution • --> 1 locally, low B  Big modes, emergent e-m effects  Unique opportunity to study electron scale turbulence Localized scattering volume k = 20 cm-1 k = 10 cm-1 13 cm fwhm 4 cm fwhm Instrument selectivity, from ray tracing Synakowski, TTF Napa 2005

  17. Synakowski, TTF Napa 2005

  18. Linear GS2 calculations predict instabilities in the gradient region, but not on the region with smaller gradients g, wExB (x106 s-1) 7 MW H-Mode • Is it the weak shear in the core? 1.0 Te ITG-TEM wExB Redi, Core WG II, Th. AM µ-tearing (kqri ≈ 1-4) 0.5 ETG 0.2 0.4 0.6 0.8 r/a Synakowski, TTF Napa 2005

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