# Presentation: 805464

## High speed images of edge plasmas in NSTX 

**High speed images of edge plasmas in NSTX **

**IEA Workshop****Edge Transport in Fusion Plasmas**
- September 11-13, 2006
- Kraków, Poland

- GPI outer midplane – shot 118152 – 208.762 ms to 208.837 ms

- 2cm

- 2cm

**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

## Outline

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

## Typical NSTX parameters

**General**
- R ~ 0.85 m    a ~ 0.7 m
- Baxis = 4.5 kG
- Ip = 0.7-1.2 MA
- PNBI < 7 MW
- Te(0) ~ 1 keV
- ne(0) ~ 2.5 x 1013 cm-3
- <ne> ~ 2 x 1013 cm-3

**Outer edge **(Rmid = 1.46 m)
- ne ~ 5 x 1012 cm-3
- Te ~ 13 eV ~ 10-3
- Ln ~ 2 cm
- s ~ 0.2 cmei ~ 6 x 106 s-1
- Lc ~ 5 m (connection length to divertor)ei/Lc ~ 0.05
- q = (BT/Bpol)(R/A) ~ 2
- LRBM ~ 1 cm
- (shot 108332 at 0.18s)

**Center stack****(18.5 cm radius)**

**Carbon tiles**

## Phantom 7 camera

**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 s
- Digitization: 12-bit
- Full discharge coverage (2 GB of on-board memory)

**Complex filament structure and dynamics**

**Good performance, long pulse at 1 MA**

- Clip:	**no filter**	2 s exposures
- 	7 ms at 100000 frame/s	playback at 150 s/s

- 1 MA - 4.0 MW NBI - Double null

## 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 D (He) light fromgas puff:     **I ******** n****o****n****e ****f(n****e****,T****e****)    **(****** ****n****e************T****e******)**                               **with 0.5 < ****, **** < 2
- D (He) emission only seen in range          **~ 5 eV < T****e**** < 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.

## GPI: L-H Transition

**GPI: L-H Transition**

**Transition takes place at ~192.1 ms**

- L-mode

- Separatrix

- Antenna limiter shadow

- 23 cm radial

- 23 cm poloidal

**Spontaneous transition into quiescent H-mode**

- “Blobs”

**Ohmic ****H-mode**

**~8 ********s between frames**
- 0.65 ms mosaic
- D2 puff
- D filter

## GPI: “Quiescent” H-mode

**GPI: “Quiescent” H-mode**

- Separatrix

- Antenna limiter shadow

- 23 cm radial

- 23 cm poloidal

**Ohmic ****H-mode**

- L-H transition takes place at ~192.1 ms

**~8 ********s between frames**
- 0.65 ms mosaic
- D2 puff
- D filter

## GPI: Active H-mode

**GPI: Active H-mode**

**H-mode edge with “blobs” ...micro-ELMs?**

- Separatrix

- Antenna limiter shadow

- 23 cm radial

- 23 cm poloidal

- “Blobs”

- Active

- Active

- Quiet

- Quiet

- 4.5 MW NBI

**~8 ********s between frames**
- 0.65 ms mosaic
- D2 puff
- D filter

## Quiescent vs. active H-modes

**Quiescent vs. active H-modes**

**Gas puff  imaging**
**D****2**** puffs**
**FOV: 23cm x 23 cm**

**Quiescent**
- 900 kA
- Ohmic
- Lower single null

**Active**
- 1 MA
- 4.7 MW NBI
- Lower single null

**poloidal**

**R**

**D****2**** puff**

- Clip:	**D******** filter**	3 s exposures
- 	5 ms at 120000 frame/s	playback at 125 s/s

## Turbulence/blob activity during H-mode

**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 n****e**** (10****13**** cm****-3****)**

**Pedestal T****e**** (eV)**

**Pedestal P****e**** (kPa)**

## Blob history

**232.291 ms**

**232.366 ms**

- Shot 118152

- Radial

- Poloidal

**75 ********s**

**Blob history**

**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**

- Secondary blob

- 2cm

- 2cm

- Separatrix

- Antenna limiter shadow

- 8.3 s

## SOL flows

**SOL flows**

- 2cm

- 2cm

**208.853 ms**

- Separatrix

- Antenna limiter shadow

- SOL flows (“wind”) visible

- Shot 118152

**208.738 ms**

- Blob “shread” upward

- 2cm

- 2cm

**309.898 ms**

**310.014 ms**

- Shot 116107

**~8 ********s between frames**
- D2 puff/D filter

## Small ELM (“Type V”) filament: propagating ionization front

**Small ELM (“Type V”) filament: propagating ionization front**

- 800 kA
- 6.5 MW NBI
- Lower single null
- Type V ELMs

**23 cm poloidal**

**23 cm radial**

- Clip:	**D******** filter**	3 s exposures
- 	5 ms at 120000 frame/s	playback at 125 s/s

**separatrix**

**limiter****shadow**

- Type V ELM filament ribbon

**Tangential edge imaging**
**NO gas puff**

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

**Type V ELM: ********W/W < 1%**

## Filament coincident in time with divertor signature

**Filament coincident in time with divertor signature**

**Interferometer**

- K.C. Lee (UC-Davis)

**Mirnov array**

- J. Menard (PPPL)E. Fredrickson (PPPL)

**1**

**2**

**3**

**7**

**USXR arrays**

**Filament also carries current**
- ~400 A

**I****p**

**Line average density (10****19**** m****-3****)**

**USXR**

**Divertor light**

**I****USXR**** (a.u.)**

**I****vis**** (a.u.)**

**Toroidal angle (deg.)**

**300**

**200**

**100**

**0**

**Chord #1**

**Chord #2**

**Chord #3**

**Chord #7**

**Midplane chord**

**BII**

**0**

**100**

**200**

**300**

**NSTX plan view (midplane)**

- K. Tritz (JHU)

- R. Maingi (ORNL)

## Small ELM (“Type V”) filament: no detachment

- Toroidal velocity: ~8 km/s (~0.9 kHz at R~1.45 m)  **...counter I****P**** and plasma rotation**
- Radial velocity: **≤0.2 km/s**
- Current: **~400 A** (~100 kA/m2)  **...co-I****P**
- 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

## After large ELMs edge similar to L-mode edge

**After large ELMs edge similar to L-mode edge**

**Gas puff  imaging**
**Field of view****23 cm x 23 cm**

**L-mode**
- 800 kA
- 2 MW NBI
- Lower single null

**H-mode**
- 1 MA
- 4.7 MW NBI
- Lower single null

- Clip:	**D******** filter**	3 s exposures
- 	5 ms at 120000 frame/s	playback at 125 s/s

**poloidal**

**R**

**D****2**** puff**

**ELM at ~221.1 ms**

- Click on image above to play movie clip.
- (Caution: 23 MB file)

## 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.**

## 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).