APS 05 poster

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High speed images of edge plasmas in NSTX
R. J. Maqueda Nova Photonics Inc., USA in
collaboration with R. Maingi, T. Munsat, J. R.
Myra, D. P. Stotler, A. E. White, S.J. Zweben
and the NSTX Research Team
2cm
2cm
GPI outer midplane shot 118152 208.762 ms to
208.837 ms
IEA WorkshopEdge Transport in Fusion
Plasmas September 11-13, 2006 Kraków, Poland
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Outline

• Introduction National Spherical Torus Experiment
  (NSTX) and diagnostics
• Edge turbulence Gas Puff Imaging (GPI) images
• Edge Localized Modes (ELMs)
• Summary

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Typical NSTX parameters
General R 0.85 m a 0.7 m Baxis 4.5 kG Ip
0.7-1.2 MA PNBI lt 7 MW Te(0) 1 keV ne(0)
2.5 x 1013 cm-3 ltnegt 2 x 1013 cm-3
Center stack(18.5 cm radius)
Carbon tiles
Outer edge (Rmid 1.46 m) ne 5 x 1012 cm-3 Te
13 eVb 10-3 Ln 2 cm rs 0.2 cmnei 6 x
106 s-1 Lc 5 m (connection length to
divertor)lei/Lc 0.05 q (BT/Bpol)(R/A)
2 LRBM 1 cm (shot 108332 at 0.18s)
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Complex filament structure and dynamics
Good performance, long pulse at 1 MA
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 (2 GB of on-board memory)
1 MA - 4.0 MW NBI - Double null
Clip no filter 2 ms exposures 7 ms at 100000
frame/s playback at 150 ms/s
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GPI Diagnostic

• Camera used to view visible emission from edge
  just above midplane.
• Gas puff is injected to increase image contrast
  and brightness. Gas puff does not perturb local
  (nor global) plasma.
• Emission filtered for Da (He) light fromgas
  puff I ? none f(ne,Te) (? nea Teb)
  with 0.5 lt a, b lt 2
• Da (He) emission only seen in range 5
  eV lt Te lt 50 eV
• View aligned along B field line to see 2-D
  structure ? B. Typical edge phenomena has a
  long parallel wavelength, filament structure.
• For more details Gas puff imaging of edge
  turbulence, R.J. Maqueda et al., Rev. Sci.
  Instrum. 74(3), p. 2020, 2003.

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GPI L-H Transition
Separatrix
23 cm radial
23 cm poloidal
Antenna limiter shadow
Blobs
L-mode
Spontaneous transition into quiescent H-mode
Ohmic H-mode
8 ms between frames 0.65 ms mosaic D2 puff Da
filter
Transition takes place at 192.1 ms
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GPI Quiescent H-mode
Separatrix
23 cm radial
23 cm poloidal
Antenna limiter shadow
Ohmic H-mode
L-H transition takes place at 192.1 ms
8 ms between frames 0.65 ms mosaic D2 puff Da
filter
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GPI Active H-mode
23 cm radial
Separatrix
Antenna limiter shadow
23 cm poloidal
Active
Blobs
Quiet
4.5 MW NBI
Active
8 ms between frames 0.65 ms mosaic D2 puff Da
filter
Quiet
H-mode edge with blobs ...micro-ELMs?
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Quiescent vs. active H-modes
R
Gas puff imaging D2 puffs FOV 23cm x 23 cm
poloidal
D2 puff
Clip Da filter 3 ms exposures 5 ms at 120000
frame/s playback at 125 ms/s
Quiescent 900 kA Ohmic Lower single null
Active 1 MA 4.7 MW NBI Lower single null
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Turbulence/blob activity during 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.

Blob activity (a.u.)
Pedestal ne (1013 cm-3)
Pedestal Te (eV)
Pedestal Pe (kPa)
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Blob history
232.291 ms

• Blob birth (frames 28156-28158)
• Detached blob polarization and ExB drift
  (frames 28159-28163)
• Blob dissipation (frames 28164-28165)
• ...at the same time the blob trail gives rise
  to a secondary blob that flows poloidally
• CAUTION Inflection points in the blob
  trajectory can be seen at all radial positions

2cm
2cm
Secondary blob
Poloidal
75 ms
8.3 ms
Separatrix
Antenna limiter shadow
Radial
Shot 118152
232.366 ms
12
208.738 ms
309.898 ms
2cm
2cm
Separatrix
Antenna limiter shadow
2cm
2cm
SOL flows
8 ms between frames D2 puff/Da filter
Blob shread upward
SOL flows (wind) visible
208.853 ms
Shot 118152
310.014 ms
Shot 116107
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Small ELM (Type V) filament propagating
ionization front
23 cm radial
Tangential edge imaging NO gas puff
Type V ELM DW/W lt 1
23 cm poloidal
Type V ELM filament ribbon

• Crossfield (poloidal) width 12 cm
• Crossfield (radial) width 3-4 cm
• Plasma within filament similar to that on
  pedestal.

separatrix
limitershadow
Clip Da filter 3 ms exposures 5 ms at 120000
frame/s playback at 125 ms/s
800 kA 6.5 MW NBI Lower single null Type V ELMs
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Filament coincident in time with divertor
signature
R. Maingi (ORNL)
NSTX plan view (midplane)
Chord 1
Chord 2
Interferometer
Line average density (1019 m-3)
Chord 3
K.C. Lee (UC-Davis)
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Ip
Chord 7
1
3
2
USXR
IUSXR (a.u.)
K. Tritz (JHU)
Midplane chord
BII
USXR arrays
Divertor light
Ivis (a.u.)
0
300
300
Mirnov array
Filament also carries current 400 A
200
Toroidal angle (deg.)
J. Menard (PPPL)E. Fredrickson (PPPL)
100
100
200
0
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Small ELM (Type V) filament no detachment

• Toroidal velocity 8 km/s (0.9 kHz at R1.45 m)
  ...counter IP and plasma rotation
• Radial velocity 0.2 km/s
• Current 400 A (100 kA/m2) ...co-IP
• Lifetime 0.5 to 1 ms
• Filament coincident in time with divertor
  signature
• Plasma within filament similar to that on pedestal

• Filament detachment not observed
• Soft ELM crash due to enhanced transport on
  perturbed flux surfaces

Blob characteristics during H-mode different from
small Type V ELMs magnetic signature,
characteristic sizes, propagation, detachment
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After large ELMs edge similar to L-mode edge
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
ELM at 221.1 ms
Click on image above to play movie
clip. (Caution 23 MB file)
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Summary

• Edge of toroidally confined plasma (like NSTX)
  show a complex filament structure and dynamics
  blobs and ELMs.
• Fast-frame imaging is a very useful tool to study
  these phenomena. Gas Puff Imaging (GPI) enhances
  the usefulness of fast imaging for edge
  turbulence studies.
• While blob (and turbulent) activity is much
  reduced in H-mode compared to L-mode, H-modes
  present a continuum from quiescent to active
  edges.
• H-mode blob activity increases with edge pedestal
  density (and pressure).
• Long-lived Type V ELM filaments have very
  different characteristics and dynamics than blob
  filaments. Type V ELM crash associated with
  enhanced transport during filament lifetime.
• Large ELMs revert edge turbulence characteristics
  to L-mode like.

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Blob, GPI and ELM structure related NSTX
papers...and references within

• High-speed imaging of edge turbulence in NSTX,
  S. J. Zweben et al., Nucl. Fusion 44 (2004) 134.
• Three-dimensional neutral transport simulations
  of gas puff imaging experiments, D. P. Stotler
  et al., Contrib. Plasma Phys. 44, 294 (2004).
• Structure and motion of edge turbulence in the
  National Spherical Torus Experiment and Alcator
  C-Mod, S. J. Zweben et al., Phys. Plasmas 13,
  056114 (2006).
• Bispectral analysis of low- to high-confinement
  mode transitions in the National Spherical Torus
  Experiment, A. E. White et al., Phys. Plasmas
  13, 072301 (2006).
• Characterization of small, Type V ELMs in the
  National Spherical Torus Experiment, R. Maingi
  et al., accepted Phys. Plasmas (2006).
• Blob birth and transport in the tokamak edge
  plasma analysis of imaging data, J. R. Myra et
  al., accepted Phys. Plasmas (2006).
• Structure of MARFEs and ELMs in NSTX, R. J.
  Maqueda et al., submitted J. Nucl. Mater. (2006).
• Derivation of time depedent 2-D velocity field
  maps for plasma turbulence studies, T. Munsat
  and S. J. Zweben, submitted Rev. Sci. Instrum.
  (2006).