o Modeling hydrocarbon generation / transport In fusion experiments John Hogan Fusion Energy Division Oak Ridge National Laboratory First Meeting Co-ordinated Research Program ” Atomic and Molecular Data for Plasma Modelling ” IAEA Vienna International Centre September 26-28, 2005
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Modeling hydrocarbon generation / transport In fusion experiments John Hogan
Modeling hydrocarbon generation / transport In fusion experiments John Hogan Fusion Energy Division Oak Ridge National Laboratory First Meeting Co-ordinated Research Program ” Atomic and Molecular Data for Plasma Modelling ” IAEA Vienna International Centre September 26-28, 2005. - PowerPoint PPT Presentation
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” Atomic and Molecular Data for Plasma Modelling ”IAEA
Vienna International CentreSeptember 26-28, 2005
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ITER tritium retention issues G. Federici, ITER GWS PSIF Workshop*
(to be published, Physica Scripta)
ITER predictions still uncertain due to – chemical erosion yields at high temperature and fluxes – effects of type I ELMs (ablation)– effects of gaps– effects of mixed materials– lack of code validation in detached plasma.
• T issues will be heavily scrutinised by licensing authorities.
• Scale-up of removal rate required is 104.• Potential options for T removal techniques for ITER.
1) Remove whole co-deposit by: • oxidation (maybe aided by RF)• ablation with pulsed energy (laser or flashlamp).
2) Release T by breaking C:T chemical bond:• Isotope exchange • Heating to high temperatures e.g. by laser, or ...
* “New directions for computer simulations and experiments in plasma–surface interactions for fusion”:
Report on the Workshop (Oak Ridge National Laboratory, 21–23 March 2005)
plate separatingion / electron sides Langmuir probe (long)
electron side
Langmuir probe (short)electron side
Optical Multichannel AnalyzerCD, C2 band intensity measurement
Limiter NeutralizerplatesD+ ion flux
CnHm generationPlasma core
top view
scrape-off layer
Schematic diagram of experiment onTore Supra Midplane Limiter (Phase II)
E Gauthier, A Cambe J Hogan et alJ Nucl Mater 2003
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Carbon production= f(D)Carbon from C3DYCarbon from C2DXCarbon from CD4
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) Roth, Garcia-Rosales Mech et al Roth PSI 13, mono-energetic Roth PSI 13 Maxwell averaged Experiment
0
0.002
0.004
0.006
0.008
0.010
0 5 10 15
BBQ comparison
Average D+ flux density( 1022 pt / m2 / s )
OH discharges(Tsurf ~ 500K)
Model comparison using partial pressure- sensitivity to sputtering model
CD emission
CD4 partial pressure
510 670 830 Tsurf(K)
LHCD: High Tsurf
PCD4∝ PD20.70 (N.Hosogane)PCD4∝D0.73 JT-60UIncreased productionof CD4 with flux
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Deuteron impact charge exchange data [Alman, Ruzic]D+ + CnDm --> D + CnD4+ Reaction Product Rate Known
(10-9 cm3/s) (total)CD4
D+ + CD4 D + CD4+ 1.880 4.150
D2 + CD3+ 1.880
D+ + CD3 D + CD3+ 1.800
D2 + CD2+ 1.800
D+ + CD2 D + CD2+ 1.700
D2 + CD+ 1.700D+ + CD D + CD+ 3.236C2D2
D+ + C2D2 D + C2D2+ 2.250 6.300
D2 + C2D+ 2.250 D+ + C2D D + C2D+ 4.358
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C2D2 C2D2+ C2D+ C2+
Heavy hydrocarbon production: dominant species frombreak-up of C2D2.BBQ calculation using Alman-Ruzic database
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Janev-Reiter database rates have been implemented in BBQ. A comparison, with the same background plasma conditions, for the Tore Supra pump limiter case, shows significant differences in comparison with the Erhardt-Langer rates
CH+ CH+ CH+
CH4 CH4 CH4
ne,LP= 2 1018 m-3
Te,LP= 20 eV Te,LP= 10 eV Te,LP= 5 eV
Janev-Reiter profiles
o
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TeLP = 20 eV
ne,LP = 2 1018 m-3
E - L
J - R
CH+ density
Axial distance (m)0.04 0.08 0.12 0.16 0.20 0.24
TeLP = 10 eV
TeLP = 5 eV
CH+ density
Axial distance (m)0.04 0.08 0.12 0.16 0.20 0.24
E - L
J - R
Axial distance (m)0.04 0.08 0.12 0.16 0.20 0.24
CH+ density
E - L
J - R
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CH+ CH+ CH+
CH4 CH4 CH4
ne,LP= 6 1018 m-3
Te,LP= 20 eV Te,LP= 10 eV Te,LP= 5 eV
Janev-Reiter profiles
o
TeLP = 20 eV
ne,LP = 6 1018 m-3
E - L
J - R
CH+ density
Axial distance (m)0.04 0.08 0.12 0.16 0.20 0.24
TeLP = 10 eV
TeLP = 5 eV
CH+ density
Axial distance (m)0.04 0.08 0.12 0.16 0.20 0.24
E - L
J - R
Axial distance (m)0.04 0.08 0.12 0.16 0.20 0.24
CH+ density
E - L
J - R
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Given D+ flux (or Cn+for self-sputter) to surface and surfacetemperature, calculate impuritytype, rate and velocitydistribution .
Mechanisms: - physical sputtering, - chemical sputtering (thermal, athermal) - RES
Impurity generationmodels
0.09
0.045
0.0
250 875 1500
T surf (K)
T e (eV)
10
30
5070 90
90
70
50
30
T e (eV)
Chemical
RES
Yield
[C / ion ]
Surface-temperature dependence of chemical and RES yields forTe=10 -> 90 eV.
- self-consistent heat flux (includes SEE, thermionic emission)
- local impurity redeposition generation due to T surf -dependent mechanisms as well as physical sputtering
- ablation cooling (Vieder model)
RDP-2000
RDP-1999
0.4 0.6 0.8 1.0 1.2 1.4 Time (s)
3
8
0
0
Carbon concentration (%)
Edge
Core
Filterscope(schematic)
0001
02
03
0411
13
12
DIII-D intrinsic impurities before/after new tile installation
Some evidence of T-dependent processes
o
0
200
400
600
800
1000
1200
1400
0 1 2 3 4 5 Time (s)
NBI
Maximum Tsurfon heated surface
2.5 mm
Ychem @ t ~ 4s
when Tmax = 1010K
Ychemmin = 1. 10-2
Ychemmax = 0.14
0 1 2 3 4 5 Time (s)
0.4
0.8
1.2
1.6
0 NBI
0.6
1.0
1.6
2.0
00 1 2 3 4 5 Time (s)
NBI
RES
Chemical
NBI
CASTEM-2000 simulation of time-dependent carbon generationfrom simulated DIII-D localized source
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C2D2
CD+C2D+C2D2+
CIC2D
Axial (30 cm)
1:1 aspect ratio shown - actual 30:1
TC2
SOL
Axial distance (along B)(cm)
0 30
0 TC 1.0(eV)
2
Axial (along B) 15:1 aspect ratio shown; actual 30:1
TC2
SurfaceMolecular temperature in the region of max. molecular
density = 0.1 - 0.3 eV
Surface SOL15:1 aspect ratio shown; actual 30:1
SOL
1:1 aspect ratio shown - actual 30:1
Near-surfacemolecular density
nC D2
+2
BBQ calculations find near-surfacemolecular rotational temperaturesto be in this range, when respectivelocalization of density and temperatureis considered.
Issues: Spectroscopy is averaged over several ELMs To be quantitative: what are heavy hydrocarbon production rates?
BBQ comparison with spectroscopy is encouraging C2D2 calculation - Allman-Ruzic-Brooks rates - vicinity of the tile gap area
Band spectroscopic modeling givesmolecular energies ~ 0.1 - 0.3 eV (R. Isler)
Axial (along B)
Surface
o
edge / pedestal only,low-field side only
Semi-empirical model for ELM transport enhancement
Green: ELM-affected region in the model
Red: C neutrals and ionsYellow: D neutrals ion ions
1
2
34
ELM event
time
radius
1
2
3
separatrix
Transport time dependence(schematic)1. Pre-ELM (barrier)2. Strong enhancement (100 μ ) sec ELM3. , 2 - Loss of barrier x pre ELM value4. - reducing to pre ELM value as barrier -is re established
- Intra ELM transportradial dependence(schematic)1. barrier2. enhancement toward SOL3. SOL radial transport
Inner leg pre-ELM detached during attached re-detaching after recovery of detachment
DIII-D experimental:fast (CID) camera
CIII evolution:M Groth et al,J Nucl Mater 2003
Modeling
solps 5.0 / Eirene99
IPP-Garching/Greifswald, FZ-Juelich
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QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Solps simulation of
CIII emission
seen by 240par
(lower divertor) camera
W Meyer,
M Fenstermacher,
M Groth
LLNL
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0 1 2 time (msec)
Prad(MW)solps
Prad(MW)BOL4/TXPN
Dα( )rel
58139Pulse
61.47 61.52 61.57 ( )time sec
12.2
0
6.1
Prad( )MWELM heat flux mitigation byInjection of extrinsic impurities
o 10 100 1000
0.1
1
10
chemical sputtering yield (per ion)
energy (eV)
N+2
Ar+
Ne+
He+
H+2 = 2 H+
Flux ratio H/ion = 400
Chemical sputtering of carbon materials due to combined bombardment by ions and atomic hydrogen W Jacob, C. Hopf, M. Schlüter, T. Schwarz-SelingerMax-Planck-Institut für Plasmaphysik Garching
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CONCLUSIONS
Intrinsic (carbon) impurity sources play a key role in ITER, both as regards erosion and for tritium retention
The ITER problem (addressed also by JET) requires a decision about the first wall material - carbon or an alternative Development of validated models for C generation, deposition and retention requires experimental comparison: this typically introduces multiple uncertainties; e.g., sputteringyield models vs hydrocarbon break-up rates
ITER relevant experimental scenarios involve fast timescale ELM events, for whichspectroscopy is an key tool
The importance of hydrocarbon generation processes has been seen in many experiments, and thus a quantitative, evaluated, integrated model for break-up processes in the plasma is needed.