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Physics and Operational Space of the Small ELM Regime in NSTX

Office of Science. Supported by. Physics and Operational Space of the Small ELM Regime in NSTX. College W&M Colorado Sch Mines Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U SNL

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Physics and Operational Space of the Small ELM Regime in NSTX

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  1. Office of Science Supported by Physics and Operational Space of the Small ELM Regime in NSTX College W&M Colorado Sch Mines Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Maryland U Rochester U Washington U Wisconsin • Rajesh Maingi • Oak Ridge National Laboratory • R.J. Maqueda 2), K. Tritz 3), M.G. Bell 4), R.E. Bell 4), C.E. Bush 1), J. Boedo 5), E.D. Fredrickson 4), D.A. Gates 4), D.W. Johnson 4), R. Kaita 4), S.M. Kaye 4), H.W. Kugel 4), B.P. LeBlanc 4), K.C. Lee 6), J.E. Menard 4), D. Mueller 4), N. Nishino 7), R. Raman 8), • A. L. Roquemore 4), S.A. Sabbagh 9), T. Stevenson 4), D. Stutman 3), S.J. Zweben 4) • 1) Oak Ridge National Laboratory 2) Nova Photonics • 3) Johns Hopkins University 4) Princeton Plasma Physics Laboratory • 5) Univ. California - San Diego 6) Univ. California - Davis • 7) Hiroshima University, Japan 8) Univ. Washington • 9) Columbia University • 47th APS Division of Plasma Physics Annual Meeting • Denver, Colorado • Oct. 24, 2005 Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAERI Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec Page 1

  2. Good performance, small ELM regime observed in NSTX • Best confinement relative to scalings • Reduced volt-second consumption -> longer pulse • dN/dt less than ELM-free but more than with larger ELMs • Important for ITER, which needs a high performance, small ELM regime to stay below the target ablation limit • Overview of ELM regimes • Operational window • Small ELM signatures • Visible cameras • Magnetics and soft X-rays • Summary and Conclusions NSTX ParametersValue Major Radius 0.85m Minor Radius 0.67m Plasma Current 1.5 MA Toroidal Field 0.45T NBI/RF Heating7.4/6 MW Page 2

  3. Small ELMs enable good performance for long pulses in NSTX D. Gates, Invited Talk FI1.02, Tuesday Double-null, biased slightly down TF coil limited Double-null OH coil limited 17425 17424 PNBI/10 [MW] PNBI/10 [MW] bN bN Big ELMs Little ELMs Page 3

  4. WMHD [kJ] Da[au] Large (Type I) Mid (Type III) Small (Type V) Mixed (I + V) Energy drop per small ELM below equilibrium reconstruction statistical noise DWMHD/WMHD~ 3-15% Pheat >> PL-H DWMHD/WMHD~ 1-5% Pheat> PL-H DWMHD /WMHD< 1% Wide Pheat range DWMHD /WMHD< 30% High Pheat,bN #108015 #112525 #111543 #117414 Page 4

  5. Specific characteristics differentiate Type V ELMs from other ELMs • Divertor Da has “hashy” or “grassy” character, but composed of individual events • Filamentary signatures on ultra-soft X-rays and interferometers at different toroidal locations • Short-lived n=1 pre-cursor on near-midplane Mirnovs • Single or double open-field line event on visible camera • Single or double filamentary rotating perturbation • Similar to grassy ELMs without bp threshold • Similar to high b Enhanced Da and High Recycling Steady Regimes without edge quasi-coherent mode • Similar to Type II ELMs except that reduced edge magnetic shear needed for this regime Page 5

  6. USXR [au] D [au] WMHD [kJ] #108729 Small ELMs are distinct, individual perturbations with signatures on Da and ultra-soft X-Rays L-H  PNBI/10 [MW] bN Time window expanded Page 6

  7. Type V ELMs observed in shapes biased away from balanced double-null, i.e. reduceddrsep drsep [cm] ne[1019 m-3] Da[au] Down Down Up Up Z (m) #112523@301ms #112498@301ms Type III Type V Da[au] Da[au] Da[au] R (m) Page 7

  8. k=2.2 d=0.75 k=2.2 d=0.75 Type V and Mixed (Type I + V) ELM regimes separated by bN and/or pedestal n*e • Minimum n*e for Type V may decrease with shaping Ip: 0.6-0.9 MA, Bt=0.45 T, PNBI: 2-6 MW, LSN, k=2.0, d=0.4 Page 8

  9. Outline • Overview of ELM regimes • Operational window • Small ELM signatures • Soft X-rays and magnetics • Visible cameras • Summary and Conclusions Page 9

  10. Filamentary structure observed in ultra-soft X-rays Perturbation enters field of view K. Tritz poster RP1.024 Page 10

  11. In Out Up Down Up Down In Out Views Down Midplane Up Midplane Down Up Filamentary structure observed in ultra-soft X-rays Page 11

  12. In Out Up Down Up Down In Out Views Down Midplane Up Midplane Down Up Filamentary structure observed in ultra-soft X-rays Page 12

  13. In Out Up Down Up Down In Out Views Down Midplane Up Midplane Down Up Filamentary structure observed in ultra-soft X-rays Page 13

  14. In Out Up Down Up Down In Out Views Down Midplane Up Midplane Down Up Filamentary structure observed in ultra-soft X-rays Page 14

  15. Filamentary structures observed in interferometry, propagating counter to plasma current ne [1019 m-3] CH 1 Plan View CH 2 ne [1019 m-3] ne [1019 m-3] CH 3 4 CH 4 ne [1019 m-3] 3 2 1 USXR ldiv [au] USXR mid [au] Da out, div au] Ip • Perturbation extends ~1/3 toroidal circumference and propagates < 1 toroidal revolution K.C. Lee poster RP1.030 Page 15

  16. n=1 pre-cursor to small ELMs propagates toroidally counter to Ip and poloidally away from X-point Divertor Da Wall Bz Toroidal Mirnovs Top Poloidal Mirnovs Bottom Menard Page 16

  17. n=1 pre-cursor to small ELMs propagates toroidally counter to Ip and poloidally away from X-point Toroidal Mirnovs Top Poloidal Mirnovs Bottom Menard Page 17

  18. Localized perturbation observed during small ELM crash #113024 515ms #113024 520ms Bush (ORNL) Page 18

  19. Localized perturbation observed during small ELM crash #113024 515ms Difference #113024 520ms Bush (ORNL) Page 19

  20. Type V ELM crash appears as a single filamentary structure #113024 515ms Difference m=12, n=1 field line at yN=0.995 #113024 520ms Bush (ORNL) Page 20

  21. Larger Perturbation with multiple filaments Observed in Type I ELMs #112502 510ms #112502 515ms #112502: Difference (515ms - 510ms) #112581: Difference (500ms - 495ms) Bush (ORNL) Page 21

  22. 74 ms 247 ms 370 ms 494 ms Small ELMs distinct from turbulence filaments • ELM lifetime longer than turbulence auto-correlation time ~ 30ms Turbulence Filaments 0 173 ms Toroidal gap FOV ELM Inner Strike Point Outer Strike point #109063: 0.593-0.605s Page 22

  23. 74 ms 247 ms 370 ms 494 ms Small ELMs distinct from turbulence filaments • ELM lifetime longer than turbulence auto-correlation time ~ 30ms Turbulence Filaments 0 173 ms Toroidal gap FOV ELM Inner Strike Point Outer Strike point #109063: 0.593-0.605s Page 23

  24. Divertor visible camera shows poloidal propagation of Type V ELMs in C-II light • One or two filaments propagate through existing X-point turbulence Outer strike point R. Maqueda poster RP1.014 Page 24

  25. Type V ELM observed as a single (or double) propagating perturbation in the scrape-off layer Band at R>ROSP R. Maqueda poster RP1.014 #117407 Page 25

  26. Small ELM regime compatible with good performance observed in NSTX • Generally has best confinement relative to scalings • Small transient heat loss from plasma per ELM • Requires shape bias away from double-null • Type V ELM itself appears as a single or double filamentary perturbation, rotating counter to Ip • Typically exists for 1 toroidal transit or less • Will test extrapolability to lowern*ethrough more shaping in coming campaign Page 26

  27. Backup Page 27

  28. Poloidal propagation speed of Type V ELM in the scrape-off layer varies from 0.5-2 km/sec 2.0 km/s 1.1 km/s 0.6 km/s Poloidal distance along inner leg (cm) Time (ms) R. Maqueda poster RP1.014 #112503-frames 1375-81 Page 28

  29. Type III ELMs have larger impact on scrape-off layer than Type V ELMs • Rapid inner target plasma reconnection followed by large disturbance Outer strike point R. Maqueda poster RP1.014 Page 29

  30. Type III ELM consists of multiple phases Inner leg detached Inner leg re-attached OSP bright R. Maqueda poster RP1.014 Perturbation Inner leg still bright Inner leg detached #117407 Page 30

  31. WMHD [kJ] Da [au] “Ped.” USXR hd-12 [au] “Sep” USXR Odd-n MHD 0.2-40 kHz [au] Odd-n MHD crash 40-400 kHz [au] Characteristics of Type III ELMs Little impact per each ELM Outflux from pedestal hd-14 [au] Influx to SOL Or separatrix Low frequency 2 kHz pre-cursor High frequency crash Fishbones Page 31

  32. Characteristics of “Mixed” Type I and Type V ELMs Discharge Type I ELM large DWMHD Large ELM WMHD [kJ] Da [au] Outflux from pedestal hd-12 [au] HD-12 USXR HD-14 USXR Influx to SOL Or separatrix Small ELMs hd-14 [au] 0.2-40 kHz [au] Odd-n MHD Odd-n MHD 40-400 kHz [au] Page 32

  33. Small ELMs distinct from turbulence filaments • ELM lifetime longer than turbulence auto-correlation time ~ 30ms Turbulence Filaments 0 74 ms 173 ms Toroidal gap FOV 247 ms 370 ms 494 ms ELM Inner Strike Point Outer Strike point #109063: 0.593-0.605s Page 33

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