# Presentation: 351552

## MARFE Structure and Dynamics in NSTX

**MARFE Structure and Dynamics in NSTX**

**R. J. Maqueda**
*Nova Photonics Inc., New Jersey, USA*
_**R. Maingi**_**, C. E. Bush***Oak Ridge National Laboratory, Tennessee, USA*
**K. Tritz***Johns Hopkins University, Maryland, USA*
**K. C. Lee***University of California at Davis, California, USA*
**and the NSTX Research Team**

**48****th**** APS-DPP Meeting**
- Oct. 30-Nov. 3, 2006
- Philadelphia, PA

## Complex MARFE and ELM interactions observed with fast camera in NSTX 

- MARFES observed around center stack in Double-null discharges
- Whereas large ELMs can quench a MARFE, small ELMs result in temporary or partial quenching, followed by re-formation
- The MARFE is only roughly axisymmetric, with apparent rotation in emission profiles

- See Fred Kelly’s poster **QP1.35****.**

- Outline
- Basic MARFE physics review
- MARFE/ELM dynamics with fast, visible camera
- Temporal correlation of small ELM and MARFE cycles
- MARFE structure
- Summary

## MARFE basics

**Conduction**

**Radiation**

**Thermal instability possible if *****d******L******z******/dT < 0*****, ****“radiation barrier”.**

- Different models include additional terms, see Fred Kelly’s poster **QP1.35****.**

**M**ultifaceted **A**symmetric **R**adiation **F**rom the **E**dgeB. Lipschultz et al., Nucl. Fus. 1984

**MARFE: ****Toroidal band** of low temperature, high density, high radiation plasma surrounding the center column of the device.

## MARFE dynamics (D)

**MARFE dynamics (D********)**

- 800 kA
- 6.0 MW NBI
- Double null

- Clip:	**D******** filter**	9 s exposures
- 	10 ms at 68000 frames/s	playback at 220 s/s

- 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.

## MARFE dynamics (Carbon emission)

**MARFE dynamics (Carbon emission)**

- 800 kA
- 6.0 MW NBI
- Double null

- Clip:	26 s exposures
- 	10 ms at 30000 frames/s	playback at 250 s/s

**CII (6578 ****Å****)**

**CIII (4647 ****Å****)**

**t – t****0**** (ms)**

**Enhancement factor**

**CII **(t0=368.6 ms)Shot 117130
**CIII **(t0=415.2 ms)Shot 117131
**D******** **(t0=384.4 ms)Shot 117127

**Dynamics similar** in CII and CIII compared to D.
**Enhancement factors of 6-10** typical for _all three_ CII, CIII and D.

## ELM cycle governs MARFE 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.
- ELM character and size reflected on MARFE dynamics.

**Divertor D******** (a.u.)**

**2 m**

**Midplane**

**117125**

**Upper divertor**

**Lower divertor**

**Time (ms)**

**117125**

**Divertor D******** (a.u.)**

**Smaller ELMs, smaller dynamics**

- Wide-slit “streak” compositions, D light.

## HFS ELM filament

**HFS ELM filament**

- Below MARFE, filament rotates at ~12 kHz (n=1), counter to Ip.
- MARFE precursor rotates at ~7 kHz, counter to Ip.
- No filament observed above MARFE.

**Time (ms)**

**I****ROI**** (a.u.)**

**117125**

- MARFE precursor rotation frequency slower than HFS filament rotation.

**D******** filter**9 s exposures
- 1.2 ms at 68000 frames/splayback at 108 s/s

## MARFE Precursor trajectory

**660.502 ms – 660.821 ms**

**117125**

**661.937 ms – 662.285 ms**

- Multi-exposure composites, D light.

**MARFE Precursor trajectory**

- MARFE pre-cursor almost field aligned near separatrix

- Field line pitch decreases as vertical stagnation approached
- In lab framevpl=(14.0±2.0) km/s
-   (cs ~ 4 eV for D+)

**Field line at separatrix, ********N****=1**

**Upward movement of MARFE precursor**

- LRDFIT, J. Menard, PPPL

*Parallel transport picture of MARFE movement*
-  Edges of precursor close to thermal stability.
-  Extra heat upstream pulls lower edge out of unstable conditions.
-  Particles now in warmer edge need to expand, both upstream and downstream.
-  Particles moving downstream deepen instability condition on rest of plasmoid.
-  Downstream edge grows and precursor “moves”.

## MARFE structure

**15 cm**

**10 cm**

**120524**

**150.383 ms **

******N****=0.99**

**Center stack**

**Mid-plane**

**117126**

**117131**

**117125**

**CIII****(26 ********s exp)**

**D********(9 ********s exp)**

**D********(9 ********s exp)**

- Bifurcated structure observed  in , Z plane for the MARFE precursor.
- Moving precursor acts as seed for partial, short-lived toroidal MARFE.

- MARFE structure extends within the separatrix.
- Typical poloidal extents of 5-15 cm.

**535.989 ms **

**800.276 ms**

**698.115 ms**

## Summary

- 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.
- HFS ELM filament rotates faster than MARFE precursor, and opposite to core plasma rotation.
- Pitch of precursor movement can be longer than pitch of B field.
- MARFE precursor presents a bifurcated structure in , Z plane, and MARFE extends within separatrix (******N** < 1).

**Lots of questions, lots to model!**

- See Fred Kelly’s poster **QP1.35****.**

## Backup

## Wide-slit “streak” compositions

**Time**

- “Add” slits, each of them shifted by **only** one pixel

**Time**

- 18 pixels wide(~56 cm)

- Each pixel of “streak” composition contains an average of 18 frames.