# Presentation: 147521

## XP-839: Poloidal extent and distribution of edge turbulence and intermittency

*R. J. Maqueda (Nova Photonics)**NSTX Edge Team*

**LFS vs HFS turbulence and blobs: **What is the level of turbulence (and intermittency) observed in the HFS compared with the LFS? – PIGGYBACK 2008
**LFS vs Divertor (top view): **At what flux surface is the correlation between LFS midplane blobs and divertor blob footprints lost?
**LFS vs Divertor (tangential view): **What are the characteristics of the turbulence near the X-point and private flux regions?

- NSTX’s Results Review, PPPL, Aug. 6, 2008

## X-point geometry effects

- Flux tube stretching near X-point may cause the blob (turbulence) scale length to be less than ion gyro-radius (R. Cohen, D. Ryutov, et al.):
-    - “x-point disconnection”- possibility of inducing turbulence below the X-point, without degrading midplane (R. Cohen, NF 37, p. 621, 1997).
- Poloidal extension of blob affects “circuit closure”, related to radial speed of the filaments.

**Is intermittency (i.e. blobs) seen in the divertor region?**
**   ****Yes**
**What is the relation to midplane turbulence/blobs?**
**   ****They are the same...**

## Filamentary pattern on divertor target plates

**Filamentary pattern on divertor target plates**

**Top view of bottom divertor**
**LiI filter**

**Filaments rotate toroidally (counter-clockwise as seen from above).**
**Emission structures move inward!**

## Intermittency observed on divertor target plates

**RMS fluctuation level, skewness and kurtosis increase away from outer strike point.**
**Profiles consistent with midplane measurements with midplane GPI of blobs (S. Zweben, NF 2004).**

**Intermittency observed on divertor target plates**

**LiI light average (a.u.)**

**RMS fluctuation**

**Skewness**

**Kurtosis**

## Ro = 1454.9 mm, Zo = 188.6 mm

- Ro = 1454.9 mm, Zo = 188.6 mm

- Circular flux tube (3 cm diam.) mapped to bottom divertor target plates.

## Ro = 1484.0 mm, Zo = 194.1 mm

- Ro = 1484.0 mm, Zo = 194.1 mm

- Circular flux tube (3 cm diam.) mapped to bottom divertor target plates.

## Ro = 1508.0 mm, Zo = 199.3 mm

- Ro = 1508.0 mm, Zo = 199.3 mm

- Circular flux tube (3 cm diam.) mapped to bottom divertor target plates.

## Ro = 1433.8 mm, Zo = 270.0 mm

- Ro = 1433.8 mm, Zo = 270.0 mm

- Circular flux tube (3 cm diam.) mapped to bottom divertor target plates.

- GPI rotated 135o toroidally

## Ro = 1454.9 mm, Zo = 188.6 mm

- Ro = 1454.9 mm, Zo = 188.6 mm

- Circular flux tube (3 cm diam.) mapped to bottom divertor target plates.

- GPI rotated 135o toroidally

## Movement on divertor target plates consistent with midplane blob movement

- Ro = 1471.5 mm, Zo = 107.0 mm

- Circular flux tube (3 cm diam.) mapped to bottom divertor target plates.

- GPI rotated 135o toroidally

**Movement on divertor target plates consistent with midplane blob movement**

## Good correlation between midplane intermittency and divertor intermittency 

**Good correlation between midplane intermittency and divertor intermittency **

**Cross-correlation (C****div-GPI****)**
- 0 ms lag

- Midplane GPI

**Time delayed cross-correlation consistent with movement observed**

## Filamentary structures seen near outer divertor strike point 

**Region of “good” correlation seen down to ********N**** ~1.03.**
**Additional filamentary structures seen even closer to outer strike point.**

**Analysis contiues...**

**Filamentary structures seen near outer divertor strike point **

**Tangential view of bottom divertor**
**LiI filter**

## XP-816: Edge Characterization Experiment in Highly Shaped Plasmas

*R. J. Maqueda (Nova Photonics), R. Maingi (ORNL), V. Soukhanovskii (LLNL), et al.*

**Focus on NHTX-like shape with “lowest” heat flux (i.e., high flux expansion).**
**Study divertor heat flux and radiation as function of:****    ****- injected power****    - density****    - divertor flux expansion****           ****(earlier talk, V. Soukhanovskii)**
**Use discharges to study blob generation mechanism during H-mode.**
**First part of XP run on March 27****th ****(16 total shots)****.**

****** ****~ 2.2**
******bot**** ~0.75**

- NSTX’s Results Review, PPPL, Aug. 6, 2008

## Power scan performed with fixed Ip, Bt, magnetic topology, etc.

**Power scan performed with fixed I****p****, B****t****, magnetic topology, etc.**

**Limited density scan at fixed P****NBI**** also performed**

- time (s)

- Ip (kA)

- PNBI (MW)

- ne L (1015 cm-2)

**128005**
**128012**
**128014**

**B****t**** ~ 4.5 kG**
**Use “preheat” NBI pulse to access H-mode**
**6 MW of NBI needed for H-mode access, yet L-H time not reproducible.**
**Reduced number of shots available prevented the repetition of non-optimum shots.**

## MHD bursts and irreproducible L-H transition complicate analysis of GPI turbulence/blob data

- MPTS, B. LeBlanc

**0.148 s**
**0.248 s**
**0.148 s**
**0.198 s**
**0.181 s**
**0.281 s**

**2 MW**
**4 MW**
**6 MW**

- R (cm)

- RZ~18cm (cm)

- D (a.u.)

- RMS

- Skewness

- Kurtosis

- auto (s)

**Gas Puff Imaging**

**MHD bursts and irreproducible L-H transition complicate analysis of GPI turbulence/blob data**

## MHD affects edge, including turbulence and blob physics

- t (s)

**Odd n MHD, mid f**** (Mirnov)**

**D******** RMS fluctuations****      **(R ~ 144 cm, Z ~ 18 cm)

- I/I (a.u.)

**Gas Puff Imaging**

**MHD bursts and irreproducible L-H transition complicate analysis of GPI turbulence/blob data.**
**Opportunity to study relationship between MHD and blob physics.**

- Increased fluctuation level not necessarily due to turbulence/blobs.

- 128005

**Low f (MHD)**

**MHD affects edge, including turbulence and blob physics**

## Divertor heat flux increased with NBI power but no change seen with density

**2 MW**

**4 MW**

**6 MW**

**Power scan**

**Density scan**

**R. Maingi, ORNL**

**800 Torr HFS**

**1000 Torr HFS**

**1250 Torr HFS**