Spectroscopy of hydrocarbon in low temperature plasmas :

Results from JT-60UT. Nakano

Japan Atomic Energy Agency, Ibaraki, Japan.

6-9/11/2006ITPA DSOL Meeting

Univ.of Toronto, Canada

Hydrocarbon in divertorHydrocarbon :• Chemical reaction with H, producing CxHy

Ychem > Yphys ( Low impact energy ), determining the life time of carbon plates

• Source of impurity• Co-deposition with T => Tritium inventory

=> Wall pumping• Molecular Assisted Recombination => Sink of H+

(Ex. CH4 + H+ => CH4+ + H, CH4

+ + e- => CH3 + H)• Measurement of yield : Ion flux <= Langmuir probe

CxHy flux <= Spectroscopy Difficulties in detached plasma :

Particle flux measurement ( Probe )Limited availability of CH emission rate (Spec.)

Local gas-puff system

Gas injection : CH4, CD4 , C2H4 and C2H6 at 3x1018 - 2x1019 /s

Spectroscopy : CH, CD and C2 viewing chords: Gas-puff nozzle

Background ( 10cm toroidally apart )

Te: 80o toroidally apart

X 2

CFC : Toyo tanso CX-2002Used since 1997NBI-heated Plasma exposure

11 hrs

Example of LEP measurement

4

3

2

1

0

x1016

282624Time ( sec )

CD photon flux ( ph / s )

CD4 flux = 3.7x1018

s-1

1.6 x 1016

s-1

Te = 70 eV,

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LEPCD4

CD= 3.7x1018 / 1.6x1016 ~ 230

View for the gas-puff port

View for Background

Injected CD4

Results : CH4 ,CD4 injection200

150

100

50

0

Loss-events / photon

6050403020100Te ( eV )

CD4 / CD

CH4 / CH ( PISCES-A)

CH4 / CH

• Weak temperature dependence• Similar results from PISCES-A ( Te < 25 eV )• Small isotope effect between CH4 and CD4 ,

,leading in No isotope difference between YCH4 and YCD4

( previously reported data )

detach

Intense CD emission around outer strike point in detached plasma

AttachedDetachedMARFE

Suggesting CxHy molecules dissociate/ionize/CX around the outer strike point even in detached plasmas

Langmuir probe still a good measure.

Density ramp-upNo CxHy puff

No significant change of CD emission rate during detachment

MARFE

4.0

3.0

2.0

1.0

0.0

x1018

1098765Time ( s )

CDbackground

-CD from gas puffport

~ 8 10x 18 CD4 / s

( 10Intensity

18

/ ph srm

2 )s

LEP : X 1 (CH4 / CD)

: X 0.1

CD : X1.5

YCH4 : x 15 !! suggesting D0 + C reaction€

ΓCH4

: X1.5

€

Γi

350

300

250

( oC )

4

2

0

( A )60

30

0

( eV )

Te

Is

`

LEP at detachment much higher than model calculation

1

10

100

Loss-events / photon

1 10 100Te ( eV )

CD4 / CD

CX Rate Coef. ( CH4 + H

+ )

CH4 / CD

Model with CXModel without CX

Attached : Te > 20 eV, measured LEP is close to modeledDetached: LEP trend is similar to CX rate coef.

Detach

€

LEPCD4

CD

Model for CH4 processes

€

d

dtX = neM ⋅X

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LEPCH 4

CH =ΓCH4

ICH4

CH

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=nCH4

nCH⋅D+ S +CX

XDefinition :

Rate equation :

Ex. for CH2

Steady-state solution ( dX/dt = 0 ) is used.

`

LEP at detachment much higher than model calculation

1

10

100

Loss-events / photon

1 10 100Te ( eV )

CD4 / CD

CX Rate Coef. ( CH4 + H

+ )

CH4 / CD

Model with CXModel without CX

Attached : Te > 20 eV, measured LEP is close to modeledDetached: LEP trend is similar to CX rate coef.

Detach

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LEPCD4

CD

SummaryFinished LEP data production by the local gas-puff method for CH, CD and C2 for CH4, CD4, C2H4, C2H6 in attached condition.

At detachment, • LEP does not change significantly.• CD intensity becomes strong at the strike point

( x 1.5).

• Γion becomes significantly low ( x 0.1 ) D0 + C chemical erosion at the strike point ΓCD4 becomes high ( x 1.5 )

• CD4 loss process is unknown; CX is suggested.

€

LEPCD4

CD

JT-60U all carbon machine

Dome

BaffleBaffle

PumpDiverot plates

Divertor plates

speed: 25.6 m3/s

Feedback-controlled D2 puff

Surface area : ~ 200 m2

Vessel volume : ~110 m3

Baking temperature :300 oC 150 oC ( ~ 2003 )

4000

3000

2000

1000

0

Loss-events / photon

6050403020100Te ( eV )

C2 / CD4

C2 / CH4

Results : CH4 ,CD4 injection

• Suggesting C2Hy is sputtered by chemical reaction with CH4 and C tile

• Strong temperature dependence

CH4 / C2

CD4 / C2

300

250

200

150

100

50

0

Loss-events / photon

6050403020100Te ( eV )

C2H4 / CH

C2H6 / CH

1000

800

600

400

200

0

Loss-events / photon

6050403020100Te ( eV )

C2H4 / C2

C2H6 / C2

Results : C2H4 and C2H6 injection

• C2H4 / CH > C2H6 / CH • C2H4 / C2 < C2H6 / C2 , indicating break-up process:

probability of CH and C2 production

Reasons for LEP data production

• Essential data for spectroscopic measurement of Ychem

• Wide variety of LEP for CH4 ~ 50% difference <= LEP affected by transport, due to divertor geometry• Need to measure Ychem including C2Hy

<= No systematic LEP data for C2Hy

300

250

200

150

100

50

0

Loss-events / photon

605040302010Te (eV)

JT-60U(CH)

model(CH)

TEXTOR

AUG (CH & CD)

x 2.5

(CH)

PISCES-A(CH)

3

2

1

0

Intensity (10

18

ph/sr/m

2

/nm/s)

519517515513Wavelength (nm)

C2

( A3Π

g

- X3Π

u,v

= 0 - 0)

CII (3s4P-3p4P)

3

2

1

0

Intensity (10

18

ph/sr/m

2

/nm/s)

519517515513Wavelength (nm)

LEP: Loss Events / Photon = reciprocal of the number of photons emitted until a molecule is lost.

CH and C2 measured (recent works):

Te ~ 40eV

Te ~ 10eV

Motivation for heavier hydrocarbon yield

Only CH measured (works so far) :

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ΓC2H y= IC2H y

C2 • LEPC2H y

C2

€

ΓCH4= ICH 4

CH − IC2H y

CH( ) • LEPCH4

CH

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ΓCH4= ICH 4

CH( ) • LEPCH4

CH

€

Ytotal =ΓCH4

Γion

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Ytotal =ΓCH4

+ 2 ⋅ΓC2H y

Γion