APS 05 poster

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Three-dimensional structure of MARFEs and ELMs in
the National Spherical Torus Experiment
R. J. Maqueda Nova Photonics Inc., New Jersey,
USA R. Maingi, C. E. BushOak Ridge National
Laboratory, Tennessee, USA K. TritzJohns Hopkins
University, Maryland, USA K. C. LeeUniversity of
California at Davis, California, USA E. D.
Fredrickson, J. E. Menard, A. L. Roquemore, S.
J. ZwebenPrinceton Plasma Physics Laboratory,
New Jersey, USA S. A. SabbaghColumbia
University, New York, USA and the NSTX Research
Team
17th PSI Meeting May 22-26, 2006 Hefei, Anhui,
China
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Outline
Center stack
Carbon tiles

• ELM structure and dynamics- comparison with
  blobs
• MARFE structure and dynamics

• Other edge studies in NSTX
• Divertor heat loads/reductionR. Maingi, V.
  Soukhanovskii
• Lithium coatingsH. Kugel
• Dust generation and dynamicsC. Parker, L.
  Roquemore, C. Skinner
• Blobs and neutral transportD. Stotler

Typical NSTX parameters R 0.85 m a 0.67 m k
2-2.3 Baxis 4.5 kG Ip 0.8-1.0 MA PNBI lt 7
MW Te(0) 1 keV ne(0) 8 x 1019 m-3
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Complex filament structure and dynamics
Phantom 7 camera Frame rate 68000
frames/s at 128 x 128 pixels 120000
frames/s at 64 x 64 pixels Minimum frame
exposure 2 ms Digitization 12-bit Full
discharge coverage with 2 GB of on-board memory
Clip no filter 2 ms exposures 7 ms at 100000
frame/s playback at 150 ms/s
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Divertor fast tangential imaging
NSTX poloidal cross-section
Phantom camera image
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Type V ELM Propagating perturbation

• Increased luminosity in the divertor region,
  including secondary band outside outer strike
  point.
• Single heat pulse propagates downward on inner
  separatrix, reaching X-point region.
• Downward propagation along field lines (20
  km/s) too slow to correspond to ion accoustic
  speed with TeTe,ped200 eV.

Clip CII filter (657.8 nm) 5 ms exposures 5 ms
at 100000 frame/s playback at 150 ms/s
800 kA 4.2 MW NBI Lower single null
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Cross-field structure of filament ribbon like
23 cm radial
Tangential edge imaging
Type V ELM filament ribbon
23 cm poloidal
separatrix
limitershadow
800 kA 6.5 MW NBI Lower single null Type V ELMs
Clip Da filter 3 ms exposures 5 ms at 120000
frame/s playback at 125 ms/s
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Type V ELM filament characteristics

• Well aligned with local magnetic field.
• Toroidal velocity 8 km/s (0.9 kHz at R1.45 m)
  ...counter IP and plasma rotation
• Radial velocity 0.2 km/s
• Crossfield widths 12 cm poloidal, 3-4 cm
  radial
• Current 400 A (100 kA/m2) ...co-IP
• Some ELMs show 2 filaments, separation might
  indicate n 3-4. But... no full n 3 or 4
  structure seen on diagnostics (Mirnov array).
• Lifetime 0.5 to 1 ms ...longer than the
  peeling-ballooning detonation time for NSTX.

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Edge turbulence and blobs compared to ELM
activity
R
Gas puff imaging Field of view23 cm x 23 cm
poloidal
D2 puff
Clip Da filter 3 ms exposures 5 ms at 120000
frame/s playback at 125 ms/s
L-mode 800 kA 2 MW NBI Lower single null
H-mode 1 MA 4.7 MW NBI Lower single null

• Blob characteristics during H-mode different from
  small ELMs
• After large ELMs (1 ms) edge similar to L-mode
  edge

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MARFE dynamics

• Toroidally symmetric MARFE moves downwards (ion
  ?B-drift direction).
• ELM activity in divertor region coincides with
  burn through of most of MARFE.
• Toroidally localized MARFE remnants move upwards,
  following field line.
• Upward movement stagnates and MARFE precursor
  expands into a toroidally symmetric band.
• Type I ELM (at 666 ms) burns through MARFE.

Clip Da filter 9 ms exposures 10 ms at 68000
frame/s playback at 220 ms/s
800 kA 6.0 MW NBI Double null
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The ELM cycle gives rise to MARFE precursor and
dynamics

• ELM cycle and MARFE cycle closely linked.
• Nevertheless, behavior and dimensions varies.
• Precursor of Type I ELM first reverses MARFE
  movement and then burns through MARFE.

High sensitivity scale
Medium sensitivity scale
Upper divertor
2 m
Midplane
Lower divertor
Low sensitivity scale
Divertor Da (a.u.)
117125
Time (ms)
Wide-slit streak composition
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Summary and conclusion

• Type V ELMs in NSTX are characterized by
  elongated filaments that rotate counter Ip, NBI
  and plasma rotation and have lifetimes of 0.5 to
  1 ms.
• Filaments are ribbon like, wider in the
  cross-field (poloidal) than radial direction, and
  carry a substantial amount of current.
• As filament propagate poloidally the ionization
  front is shifted and, possibly as well, the
  magnetic surfaces shift.
• Coincident with the ELM cycle the MARFE moves
  up/down the center stack.
• The toroidally symmetric MARFE is, in some cases,
  born from a precursor resulting from partial
  burnthrough of the preceding MARFE in the cycle.