PERSISTENT SURVEILLANCE FORPIPELINE PROTECTION AND THREAT INTERDICTION

Determination of Carbon Release Mechanisms in the DIII-D Divertor from Analysis of C I Line Profiles

Presented by Phil Westa

for Ralph Islerb and Neil Brooksa

aGeneral AtomicsbORNL

DSOL ITPAToronto

November, 2006

components of the 3P- 3Po Zeeman triplet of C I are used to determine the carbon production mechanism

• Physical sputtering:

o Asymmetric line shape

o Only a small red wing with respect to the rest frame wavelength because most atoms move toward the collection optics.

o Peak is shifted by -0.1 to -0.2 Å from the rest frame wavelength

• Chemical sputtering:

o Nearly symmetric line shape

o Peak shifted by only -0.03 to -0.04 Å owing to the near thermal release of parent hydrocarbon.

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Triplet sourceReconvolutionMeasured points

Relative Amplitude

Δλ ( )Å

Helium plasmas provide a good test for modeling profiles when physical sputtering is dominant.

• The red wing (Δλ is the result of reflections from the divertor tiles

• The Thompson formula, with Eimpact= 400 eV, is a good fit except near Δλ .

• An additional 9%

contribution from chemical sputtering gives the best fit to the source profile.

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SymmetricThompsonTotal modeledSource profile

Relative Amplitude

Δλ ( )Å

= Thompson91% of total

.172 Å

C I from the porous plug ( during methane injection) comes mainly from molecular dissociation.

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SymmetricSource profile

Relative Amplitude

Δλ (Α)

-.32 Å

Porous plug - methane breakup

Two Gaussian Representation of Symmetric Component

97% - 0.35 eV 3% - 5.0 eV

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SymmetricThompsonTotal modeledSource profile

Amplitude (a.u.)

Δλ ( )Å

2.56 s

= Thompson1% of total

.3 Å

T1S = .75 eV

Outer strike point: Attached L-mode

Thompson =10% TotalCold symmetric peak (aka chemical sputtering)dominates

TS1 = 0.35 eV

When divertor detachesC I Doppler shift drops to near zero

• Detached Case (solid): ne/nGW ~ 0.7 Div Thomson near OSP: ne

DIV ~2 x 1020 m-3 Te

DIV ~ 1.3 eV after t=3.0 s

• Attached Case (dashed): ne/nGW ~ 0.2 Div Thomson near OSP: ne

DIV ~2 x 1019 m-3 Te

DIV ~ 15. eV after t=3.0 s

• Suggests that C I emission in detached case is recombination dominated

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1 2 3 4 5Time (s)

(b)

Inner Strike Zone

Outer Strike Zone

Summary

• Cold, symmetric peak present in all cases studied ( detached, attached, high and low NBI power)

• Thompson peak prominent only in high power NBI, attached cases

• In detached, high density, cold divertor cases, Doppler shift of cold symmetric peak drops to values much lower than expected for chemical sputtering, probably a sign that recombination dominates the C I emission.