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Spectroscopy of hydrocarbon in low temperature plasmas : Results from JT-60U T. Nakano J apan A tomic E nergy A gency, Ibaraki, Japan. 6-9/11/2006 ITPA DSOL Meeting Univ.of Toronto, Canada
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Hydrocarbon in divertor Hydrocarbon : Chemical reaction with H, producing C x H y Y chem > Y phys ( 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. CH 4 + H + => CH 4 + + H, CH 4 + + e - => CH 3 + H) Measurement of yield : Ion flux <= Langmuir probe C x H y flux <= Spectroscopy Difficulties in detached plasma : Particle flux measurement ( Probe ) Limited availability of CH emission rate (Spec.)
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Local gas-puff system Gas injection : CH 4, CD 4, C 2 H 4 and C 2 H 6 at 3x10 18 - 2x10 19 /s Spectroscopy : CH, CD and C 2 viewing chords: Gas-puff nozzle Background ( 10cm toroidally apart ) T e : 80 o toroidally apart X 2 CFC : Toyo tanso CX-2002 Used since 1997 NBI-heated Plasma exposure 11 hrs
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Example of LEP measurement T e = 70 eV, = 3.7x10 18 / 1.6x10 16 ~ 230 View for the gas-puff port View for Background Injected CD 4
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Results : CH 4, CD 4 injection Weak temperature dependence Similar results from PISCES-A ( T e < 25 eV ) Small isotope effect between CH 4 and CD 4,,leading in No isotope difference between Y CH4 and Y CD4 ( previously reported data ) detach
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Intense CD emission around outer strike point in detached plasma Attached Detached MARFE Suggesting CxHy molecules dissociate/ionize/CX around the outer strike point even in detached plasmas Langmuir probe still a good measure. Density ramp-up No C x H y puff
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No significant change of CD emission rate during detachment MARFE LEP : X 1 (CH 4 / CD) : X 0.1 CD : X1.5 Y CH4 : x 15 !! suggesting D 0 + C reaction : X1.5
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` LEP at detachment much higher than model calculation Attached : T e > 20 eV, measured LEP is close to modeled Detached: LEP trend is similar to CX rate coef. Detach
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Model for CH 4 processes Definition : Rate equation : Ex. for CH 2 Steady-state solution ( dX/dt = 0 ) is used.
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` LEP at detachment much higher than model calculation Attached : T e > 20 eV, measured LEP is close to modeled Detached: LEP trend is similar to CX rate coef. Detach
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Summary Finished LEP data production by the local gas-puff method for CH, CD and C 2 for CH 4, CD 4, C 2 H 4, C 2 H 6 in attached condition. At detachment, LEP does not change significantly. CD intensity becomes strong at the strike point ( x 1.5). ion becomes significantly low ( x 0.1 ) D 0 + C chemical erosion at the strike point CD4 becomes high ( x 1.5 ) CD 4 loss process is unknown; CX is suggested.
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JT-60U all carbon machine Dome Baffle Pump Diverot plates Divertor plates speed: 25.6 m 3 /s Feedback-controlled D 2 puff Surface area : ~ 200 m 2 Vessel volume : ~110 m 3 Baking temperature : 300 o C 150 o C ( ~ 2003 )
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Results : CH 4, CD 4 injection Suggesting C 2 H y is sputtered by chemical reaction with CH 4 and C tile Strong temperature dependence CH 4 / C 2 CD 4 / C 2
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Results : C 2 H 4 and C 2 H 6 injection C 2 H 4 / CH > C 2 H 6 / CH C 2 H 4 / C 2 < C 2 H 6 / C 2, indicating break-up process: probability of CH and C 2 production
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Reasons for LEP data production Essential data for spectroscopic measurement of Y chem Wide variety of LEP for CH 4 ~ 50% difference <= LEP affected by transport, due to divertor geometry Need to measure Y chem including C 2 H y <= No systematic LEP data for C 2 H y
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LEP: Loss Events / Photon = reciprocal of the number of photons emitted until a molecule is lost. CH and C 2 measured (recent works): T e ~ 40eV T e ~ 10eV Motivation for heavier hydrocarbon yield Only CH measured (works so far) :
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