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Physics of Ohmically Heated H-mode Plasmas - Continuation of XP-506

Physics of Ohmically Heated H-mode Plasmas - Continuation of XP-506. C.E. Bush, S. Kubota, R. Bell, J-W. Ahn, S. Zweben, B. LeBlanc, J. Wilgen, R. Raman, K.C. Lee, L. Roquemore, R. Maqueda, E. Mazzucato, K. Tritz, L. Delgado-Aparicio, S. Medley, M. Bell, S. Kaye. NSTX Physics Meeting

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Physics of Ohmically Heated H-mode Plasmas - Continuation of XP-506

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  1. Physics of Ohmically Heated H-mode Plasmas- Continuation of XP-506 C.E. Bush, S. Kubota, R. Bell, J-W. Ahn, S. Zweben, B. LeBlanc, J. Wilgen, R. Raman, K.C. Lee, L. Roquemore, R. Maqueda, E. Mazzucato, K. Tritz, L. Delgado-Aparicio,S. Medley, M. Bell, S. Kaye NSTX Physics Meeting Monday, June 9, 2008 Princeton Plasma Physics Laboratory Princeton, NJ CEBush XP-506 OHmicH-modes June 8, 2008

  2. The Goal of XP-506: • This is a continuation of XP506 of the 2005 run. The goal of this experimental proposal is to study H-modes in which core and edge turbulence can be measured. Also a second goal is to study an H-mode with no external fast particle or momentum input in order to understand the fundamental physics of the L-H transition and the H-mode. CEBush XP-506 OHmicH-modes June 8, 2008

  3. Shot list for XP-506 05Jun2008 Shot list for the run Thursday June 5, 2008 is given below. The approximate H-mode ON (L-H-transition) and OFF times are also given: 129693 hmode 204-344 ms excellent shot *** (triple star) 129694 hmode 210-312 ms ** 129695 hmode 206-297.7 ms ** 129698 hmode 202-231 ms ** 129699 hmode 200-230 ms 129700 hmode 200-228 ms 129701 hmode 201-318.3 ms ** 129702 hmode 200-242 ms * 129704 hmode 210-235 ms 129705 hmode 206-229 ms No Hmode comparison shots 129697 No hmode 129703 No hmode H-mode from couple years ago 127256 hmode 190-300 ms CEBush XP-506 OHmicH-modes June 8, 2008

  4. NCII(t) Ti(t) RCII(t) Vi(t) emissivity Er(t) Ip(t) D(t) Time (s) Time (s) Vt, Vp, Tt, and Tp change at L-H Transition Begin H-mode at 0.20 s Vel gradients increase R. Bell CEBush XP-506 OHmicH-modes June 8, 2008

  5. FIReTIP density fluctuation change at theL/H transition (red line) of Shot 129694 KC Lee • New channel shows decrease influctuations at transition CEBush XP-506 OHmicH-modes June 8, 2008

  6. Isat Fluctuations Dramatically Reduced in H-mode - Fast reciprocating probe data by J-W Ahn L  H transition time (sec) J-W Ahn • Probe plunge reached maximum distance at L-H transition time • Isat amplitude dramatically reduced in H-mode compared to L-mode CEBush XP-506 OHmicH-modes June 8, 2008

  7. RMS fluctuation level shows different trend in L- and H-mode • Isat RMS level peaked near separatrix in both L- and H-mode • Isat RMS fluctuation level is indicated by δIsat/Isat L-Mode: Increases from separatrix into the SOL, then slightly decreases or saturates in the far SOL H-mode: Rapidly increases in the near SOL (R-Rsep up to 2-3cm), then drops and becomes saturated in the far SOL (R-Rsep ≥ 6-7cm) CEBush XP-506 OHmicH-modes June 8, 2008

  8. Isat Skewness Trend Similar to RMS Fluctuation Level • Skewness is indicative of fluctuations deviation from Gaussian • L-Mode: Increases from separatrix into the SOL, slightly decreases in the very far SOL Positive over the whole SOL region • H-mode: Rapidly increases in the near SOL and then drops in the rest of SOL Becomes negative in the very far SOL (R-Rsep~10cm) CEBush XP-506 OHmicH-modes June 8, 2008

  9. High-k result for shot 129693 CEBush XP-506 OHmicH-modes June 8, 2008

  10. Spectra of fluctuations at R=1.35 (no H-mode) CEBush XP-506 OHmicH-modes June 8, 2008

  11. H-mode no H-mode P3a P3b P3c P3d Ohmic H-modes in BEaP Probes • Far-SOL midplane density goes down suddenly at H-mode • Far-SOL density (and turbulence) can return during H-mode • Far-SOL density was dropping slowly even without H-mode Time (s) Time (s) CEBush XP-506 OHmicH-modes June 8, 2008

  12. EXTRA CEBush XP-506 OHmicH-modes June 8, 2008

  13. Er Increases by > 10 kV/m after L-H-mode Transition • Vpol increases by 30 km/s after L-H transition • Ti and Te increase after transition CEBush XP-506 OHmicH-modes June 8, 2008

  14. Spectra of fluctuations at R=1.2 (H-mode ) CEBush XP-506 OHmicH-modes June 8, 2008

  15. 1 1 1 1 1 1 2 3 3 3 3 3 3 . 0 x 1 0 T i m e s e r i e s o f c r o s s - c o r r e l a t i o n v a l u e s n e a r H - M o d e t = 0 . 2 0 9 9 2 3 s L - H t r a n s i t i o n . t = 0 . 1 9 6 0 2 - 0 . 1 9 9 1 2 s 2 . 5 x 1 0 2 . 0 x 1 0 t = 0 . 1 9 3 3 1 5 s 1 . 5 x 1 0 1 . 0 x 1 0 L - M o d e t = 0 . 1 8 5 9 8 - 0 . 1 9 4 2 4 s 5 . 0 x 1 0 t = 0 . 1 7 6 5 9 3 s 0 . 0 1 0 0 1 1 0 1 2 0 1 3 0 1 4 0 1 5 0 M a j o r R a d i u s [ c m ] 1 . 0 L - M o d e 0 . 8 0 . 6 0 . 4 0 . 2 H - M o d e 0 . 0 0 2 4 6 8 1 0 1 2 1 4 1 6 R a d i u s [ c m ] D Correlation Length Decreases atL-H Transition S. Kubota • Typical Lcr drops from ~10-20 cm to ~ 4-8 cm at the L-H transition. • Eventual rise in edge density cuts off reflectometer signal • For the 42 GHz channel, statistical properties of signal (amplitude histogram, complex spectrum) remain constant across transition, with turbulence properties close to axis changing little e - f o l d i n g L ~ 1 4 c m c r L ~ 3 . 5 c m c r CEBush XP-506 OHmicH-modes June 8, 2008

  16. 116326, 116327, 0.227 s 116326, 116327 ELM-Free OHH-mode Obtained with LSN 4 0.8 H-mode H-mode Te (keV) ne (1019/m3) 2 0.4 L-mode L-mode 0 0.0 180 0 40 80 120 160 0 40 80 120 Radius (cm) Radius (cm) 2 4 4 Ip(MA),Te (keV),Dα(arb) 2 2 Pe (kPa) 1 ne L(1019/m2) 0 0 0 B. LeBlanc 0.0 0.1 0 40 80 120 160 0.2 0.3 Radius (cm) Time (s) CEBush XP-506 OHmicH-modes June 8, 2008

  17. [ ] 1 T d n d T i i i E V B V B + - = + r q f f q Z e n d r d r i i Model: E x B Flow Shear Breaks Turbulent Eddies to Transition to a Quiescent State • Sheared ExB flow is expected to suppress turbulence leading to enhanced core confinement • The ExB flow is determined from the zeroth order force balance equation for any species i: • Er can be solved for by using measured profiles of: ni, Ti, VФ: using charge exchange recombination spectroscopy (CHERS) Bθ from MSE, combined with TRANSP simulations CEBush XP-506 OHmicH-modes June 8, 2008

  18. Gas Puff Imaging (GPI): L-H transition L-H Transition takes place at ~192.1 ms L-mode “Quiescent” H-mode H-mode R. Maqueda D (arb.) 0.6 Shot 115513 0.4 0.2 0 0.05 0.10 0.15 0.20 0.25 0.30 Time (s) CEBush XP-506 OHmicH-modes June 8, 2008

  19. Turbulence/blob activity much lower During Ohmic H-mode than L-mode and NBI H-mode • The characteristics of the H-mode turbulence and blobs present a continuum from a turbulence level just above that measurable (a “quiescent” H-mode) to that approaching L-mode level (an “active” H-mode), at least for brief periods of time. • The level of activity correlates well with the pedestal ne or Pe. H-mode Blob activity (a.u.) OH H-mode OH H-mode OH H-mode L-mode (no pedestal, “edge parameters”) Pedestal ne (1013 cm-3) Pedestal Te (eV) Pedestal Pe (kPa) R. Maqueda CEBush XP-506 OHmicH-modes June 8, 2008

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