# Presentation: 758368

## Particle and power exhaust in NBI-heated plasmas in NSTX

**Particle and power exhaust in NBI-heated plasmas in NSTX**

***Culham Sci Ctr***
***U St. Andrews***
***Chubu U***
***Fukui U***
***Hiroshima U***
***Hyogo U***
***Kyoto U***
***Kyushu U***
***Kyushu Tokai U***
***NIFS***
***Niigata U***
***U Tokyo***
***JAERI***
***Hebrew U***
***Ioffe Inst***
***RRC Kurchatov Inst***
***TRINITI***
***KBSI***
***KAIST***
***ENEA, Frascati***
***CEA, Cadarache***
***IPP, J******ü******lich***
***IPP, Garching***
***ASCR, Czech Rep***
***U Quebec***

***College W&M***
***Colorado Sch Mines***
***Columbia U***
***Comp-X***
***General Atomics***
***INEL***
***Johns Hopkins U***
***LANL***
***LLNL***
***Lodestar***
***MIT***
***Nova Photonics***
***New York U***
***Old Dominion U***
***ORNL***
***PPPL***
***PSI***
***Princeton U***
***SNL***
***Think Tank, Inc.***
***UC Davis***
***UC Irvine***
***UCLA***
***UCSD***
***U Colorado***
***U Maryland***
***U Rochester***
***U Washington***
***U Wisconsin***

**V. A. Soukhanovskii****a****, R. Maingi****b****, C. J. Lasnier****a****, **
**L. Roquemore****c****, R. E. Bell****c****, J. Boedo****d****, E. Bush****b****, **
**R. Kaita****c****, H. W. Kugel****c****, B. P. LeBlanc****c****, J. Menard****c****, **
**D. Mueller****c****, S. F. Paul****c****, R. Raman****e****, S. Sabbagh****f**
***a ******Lawrence Livermore National Laboratory, Livermore, CA, USA***
***b ******Oak Ridge National Laboratory, Oak Ridge, TN, USA***
***c******Princeton Plasma Physics Laboratory, Princeton, NJ, USA***
***d******University of California at San Diego, La Jolla, CA, USA***
***e ******University of Washington, Seattle, WA, USA***
***f******Columbia University, New York, NY, USA***

## Abstract

**Abstract**

**This research is supported by the U.S. Department of Energy under contracts No. W-7405-Eng-48 at ****LLNL**** and DE-AC02-76CH03073 at ****PPPL****.**

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Thesis

- Divertor heat load mitigation - one of the key Boundary Physics issues in large aspect ratio tokamaks, more so in Spherical Tori (ST)
- Study divertor regimes at low aspect ratio in NSTX (A = 1.35, qout < 10 MW/m2)
- NSTX divertor (open, no active pumping): inner leg is naturally detached at *P**in* > 1 MW, *n**e* > 2-3 x 1019 m-3, outer leg is never detached
- In a dedicated experiment D2 injection from private flux region produced outer leg detachment in 4 MW NBI-heated H-mode
- Neon injections did not result in outer leg detachment

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Outline

**Outline**

-   NSTX background: parameters, heat / particle fluxes, divertor asymmetries
-   Naturally occurring divertor regimes in NSTX
-   Dedicated D2 and neon injection experiments to develop and study dissipative divertor regime compatible with high performance H-mode plasmas
-   Summary

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## NSTX reference data

**NSTX fueling**
-  Gas injection: low field side (LFS, top + side), high field side (HFS, midplane + shoulder), private flux region.  D2, He, injected at  S = 20 - 120 Torr l /s.
-  Neutral beam injection system: three beams,  80 - 100 keV, 6 MW, fueling rate: S < 4 Torr l / s
-  Supersonic gas injection: S = 60 Torr l / s
**NSTX wall conditioning**
-  Between shots He GDC
-  He conditioning plasmas
-  TMB and  Plasma TMB
**NSTX pumping**
-  Turbomolecular pump
- 	(3400 l / s)
-  NBI cryopump
- (50000 l / s)
-  Conditioned walls
**PFC**
** **ATJ graphite tiles on
- divertor and passive  plates
-  ATJ and CFC tiles on center stack
-  Thickness 1” and 2”

**NSTX reference data**

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Many useful diagnostics to study SOL and divertor

** ****IRTV**: two Indigo Alpha 160 x 128 pixel microbolometer cameras, 7-13 m range,
- 30 ms frame rate
** ****D********, D********, C III filtered cameras**: four Dalsa
- 1 x 2048 pixel CCDs, filter FWHM 10-15 A,
- frame rate 0.2 - 1 ms
-  **Neutral pressure gauges**: four microion gauges on top and at midplane, two Penning gauges in lower and upper divertor,  time response 5-10 ms
-  **High-resolution spectrometer** (“VIPS 2”): ARC Spectro-Pro 500i, three input fibers (channels), time response 15-30 ms,
-  FWHM > 0.6 A
-  **Bolometry**: midplane (AXUV radiometer array), divertor - ASDEX-type four channel bolometer, time response 20 ms
-  **Langmuir probes**: midplane - fast probe, tile LPs - *I**sat*, *T**e  *measurements
-  Midplane **Multi-point Thomson** scattering with 2-4 points in SOL

**Many useful diagnostics to study SOL and divertor**

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Impact of ST geometry effects on SOL and divertor physics is studied in NSTX

-   High SOL mirror ratio *M=|B**min**| / |B**max**|* - affects connection length *L**||** , *fraction of trapped particles *f, *etc
-  Large flux expansion ratio                 :
- 	- Heat and particle in-out asymmetries
- 	- Parallel transport, divertor regimes
-  Compact divertor - divertor volume, PFC plasma-wetted area

**Impact of ST geometry effects on SOL and divertor physics is studied in NSTX**

**In NSTX P****in****/R < 9**

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Heat flux, recycling, impurity divertor profiles

**In lower single null plasmas:**
-  Heat flux increases non-linearly with Pin
-  qin/qout= 2-3
-  Heat flux equilibration time eq~ 100 ms
-  Recycling strong in divertor
-  High neutral pressure (0.1-0.2 mTorr)
-  Neutral compression ratio is 5-10

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Divertor in-out asymmetries observed

**Divertor in-out asymmetries observed**

-  Heat flux asymmetry always qout/qin > 1, consistent with
- 	- SOL area factor: Aout= 3 x Ain
-            - Magnetic flux expansion factor (mid/div): fin > fout
- 	 - Large Shafranov shift
-  	- Core / edge in-out transport asymmetry
-  D asymmetry (particle flux / recycling) through most of op. space
-            - Density and power dependent
-            - Not always correlated with volume recombination onset
-            - Complex interplay of cold dense opaque detached 3D plasma and diagnostic geometry effects?

- Op. Space where divertor D asymmetry > 1.5

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Inner divertor detached in NBI-heated plasmas

**Inner divertor detached in NBI-heated plasmas**

-  Inner divertor detached naturally at *<n**e**>* = 2.5-3 x 1019 m-3

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## High ne, low Te inferred from Balmer series lines measured in inner divertor 

**High *****n******e*****, ****low *****T******e***** inferred from Balmer series lines measured in inner divertor**** **

-  FWHM increases with *n*, Voigt line profile shape
-  Inglis-Teller limit for *n*=14 yields *n**e*=1021 m-3 (too high!)
-  Stark broadening of *n*=8 yields *n**e*= 1-5 x 1020 m-3
-  Analysis with CRETIN in progress
-  From line intensities (Saha-Boltzman population distribution): *T**e *= 0.3-1.0
-  Inner divertor oscillating MARFE often seen on cameras

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Outer divertor is in linear and high-recy. regime

- 	max measured q =10 MW/m2
-  **Outer divertor is in sheath-limited and high-recycling regime**
** ****Short connection length + L****c**** (carbon) = not detached at high *****n******e***** **
-  Uncertainty in LCFS position 1-2 cm:
-    - MPTS midplane *T**e* = 5 - 40 eV
-    - Fast midplane probe *T**e* = 10 - 30 eV
-    - SOL collisionality  = 5 - 60
-  Divertor *T**e* = 5 - 40 eV
-  Very weak dTe/dx||
-   (e-i partition, heat
-   transport mechanism)
-  Carbon radiation
-    zone is 10 eV

**Outer divertor is in linear and high-recy. regime**

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Flat Te, ne in outer midplane SOL

**Midplane fast probe**
**- J. Boedo (UCSD)**

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Moderate  plasma used for detachment studies

|  | 1.85 |
| --- | --- |
|  | 0.4 |
| Drsep (cm) | 1.0-1.5 |
| qedge | 13 |
| LII, inner (m) | 8.3 |
| LII, outer (m)  | 6.0 |
| M 
(Mirror ratio) | 5.0 |
| f inner
(Flux expansion) | 2-3 |
| f outer
(Flux expansion) | 2-3 |

- D2

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Detach outer divertor by injecting D2

-   Used PF2L shape, 4 MW NBI at *B**t **= *0.45 T
-  Injected D2 in LFS midplane at 20 - 120 Torr l / s
-    PFR at 0 - 15 Torr l / s, HFS at 40-65 Torr l /s
-  Concluded divertor detachment from D/D ratio, peak heat flux reduction
-  Sign of volume recombination (DD) in outer divertor at 100 Torr l / s, or with HFS+PFR injector at 65 Torr l / s
-  D2 puffing from midplane injectors brings outer outer SOL close     to detachment threshold, however plasma hits operational limit
-    (locked modes, large low m,n MHD modes, confinement
-     degrdation)

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Scan outer SOL collisionality by gas puffing

**D******

**Inner**

**Inner**

**Inner**

**Outer**

**Outer**

**Outer**

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Outer divertor peak heat flux reduced x4 by D2 injection in private flux region

**D******

**Inner**

**Inner**

**Inner**

**Outer**

**Outer**

**Outer**

-  D2 puffing from PFR reduces peak *q**out*  four-fold
-  No change in inner divertor - peak *q**in** *= 0.5 MW/m2
-  Divertor radiation increases (difficult to quantify -   poor bolometric coverage
-  Interim IRTV calibration used

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Inner divertor D / D increases x2 during D2 injection from PFR

-  No change in detached inner divertor - D / D
-  Interim D, D camera calibration used

**Inner divertor D******** / D******** increases x2 during D****2**** injection from PFR**

**D******

**Inner**

**Inner**

**Inner**

**Outer**

**Outer**

**Outer**

- time

- R

- R

**D******

**D******

**Inner**

**Outer**

**Inner**

**Outer**

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## UEDGE detachment space is close to experiment

**UEDGE detachment space is close to experiment**

-  H-mode LSN equilibrium used
-  UEDGE diffusive transport model
-  Impurities included
-  Outer *n**e**, T**e* profiles matched, D and IRTV not matched
-  For guiding purposes only

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Detachment observations consistent with 2PM

**Detachment observations consistent with 2PM**

**P. C. Stangeby, *****The plasma boundary of Magnetic Fusion Devices*****, IoP Publishing, Bristol & Philadelphia, 2000**

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Neon injections did not detach outer divertor

**Neon injections did not detach outer divertor**

- Neon

-  Neon puffed into 4 MW H-mode
-  Did not cause H-L transition
-  Puffing rate 1.5 x 1020 s-1
-  Prad = 0.3 x Pin
-  Outer peak heat flux reduced x4

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain

## Summary

- D2 and neon injections were used to attempt detachment of outer divertor leg in 3-4 MW NBI-heated L- and H-mode plasmas
- Clear signs of outer leg detachment were obtained in 4 MW H-mode plasmas with D2 injections from the private flux region (PFR). Peak heat flux at the outer divertor target was reduced four-fold from
-    2 MW/m2 to 0.5 MW/m2. During D2 injections from PFR spectroscopic diagnostics indicated the onset of volume recombination in the outer leg, where D/ D ratio increased two-fold and approached the value measured in the detached inner divertor
- Midplane gas injectors alone with D2 fueling rate up to 110 Torr l / s failed to produce SOL conditions necessary for outer divertor leg detachment
- Up to four-fold reduction of the peak heat flux on the outer target was measured in 4 MW NBI-heated H-mode and L-mode plasmas with Ne injections. Outer divertor leg remained attached.  Prad / Pin was > 30 %

- V. A. Soukhanovskii,  32nd EPS, June 2005, Tarragona, Spain