spectroscopy of hydrocarbon in low temperature plasmas : results from jt-60u t. nakano j apan a...
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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
€
LEPCH 4
CH =ΓCH4
ICH4
CH
€
=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
€
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.
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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) :
€
ΓC2H y= IC2H y
C2 • LEPC2H y
C2
€
ΓCH4= ICH 4
CH − IC2H y
CH( ) • LEPCH4
CH
€
ΓCH4= ICH 4
CH( ) • LEPCH4
CH
€
Ytotal =ΓCH4
Γion
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Ytotal =ΓCH4
+ 2 ⋅ΓC2H y
Γion