1 th loarerfuel retention in tokamaks – psi conference 26-30 may - toledo euratom th loarer with...
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1Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom
Th Loarer
with special thanks to
N Bekris, S Brezinsek, C Brosset, J Bucalossi, P Coad, G Esser, W Fundamenski, E Gauthier, A Kreter, J Likonen, B Lipschultz, M Mayer,
P Monier-Garbet, Ph Morgan, R Neu, B Pégourié, V Philipps, R Pitts, V Rohde, J Roth, M Rubel, C Skinner, J Strachan, E Tsitrone.
And alsoEU TF on PWI and JET EFDA contributors
Fuel retention in tokamaks
2Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom
OUTLINE
- Introduction
- Evaluation of fuel retention in tokamaks
- Gas Balance
- Post mortem analysis
- Extrapolation to ITER
- Summary
3Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Introduction
- Evaluation of hydrogenic retention in present tokamaks is of high priority to
establish a database and a reference for ITER (400 s…usually 10-20 s today).
- T retention constitutes an outstanding problem for ITER operation particularly
for the choice of the materials (carbon ?)
- A retention rate of 10% of the T injected in ITER would lead to the in-vessel T-
limit (350/700g) in ~35/70 pulses.
- Retention rates of this order or higher (~20%) are regularly found using gas
balance.
- Retention rate often lower (3-4%) are obtained using post mortem analysis
4Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom
D,T
Wall
Mechanisms for fuel retention
Two basic mechanisms for
Long term fuel retention
Deep Implantation, Diffusion/Migration, Trapping
C, Be C, Be, D ,T
Codeposition
Short term retention (Adsorption: dynamic retention)
~ Recovered by outgassing
In tokamaks today Two complementary methods
Gas balance How much ? During the pulse / integrated pulse/days.
Post mortem Where and how? Integrated over experimental campaign
5Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Gas balance
Divertor cryo-pumps
PlasmaCalibrated Particle Source
(Gas, NBI, pellets)
Exhaust by NBI boxes, Diag…
Retention
Short & Long Term
1 - Function of time - Measurement of the Injected and pumped fluxes (Pressure gauges and pumping speed) 2 - Integral of Pumped flux + intershot outgassing (~ Short Term Ret ) (Collected in a calibrated volume).
Separate Short and long term retention
Gas Balance Retention = Injection - Pumped + Plasma
6Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Retention: Short and long term
Short term retention- Depends on plasma scenario, wall conditioning and Material (Be, C)…-“Limited” to “fast” reservoir and recovered in between pulses (outgassing)
Actively cooled device Steady state operation-->Long term retention
Long term retention
- Co-deposition Correlated to C production
- Implantation Edge plasma, material structure…
Long term retention
Short term retention
5
4
3
2
1
0
1020
Ds-1
4003002001000
Time (s)
# 32299 # 32300
TS
Dynamic retention: ≈ 5 x1021D JET ≈ 2.5 1022 D ~ wall area ratio
7Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Plasma scenario: C prodution
- Long term retention- Drop by ~60% when moving from L-mode to Type III H-mode.- Increases by ~60% when moving from L-mode to Type I H-mode.
Retention correlated to increase of C erosion
T Loarer et al., EPS 2007
Pulse type Divertor phase (s)
Injection(Ds-1)
Long term retention (Ds-1)
L-mode
2 MW
126 ~1.81022 1.341021
Type III
6 MW - <5-10 kJ
350 ~0.61022 0.81021
Type I
13 MW – 100 kJ
50 ~1.71022 2.081021
Series of repetitive and consecutive discharges (~no history effect)
8Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Carbon production and scenario
- DTE on JET and TFTR (at high NBI power more T retention by co-deposition)
C Skinner et al. JNM 1997, 1999
J Strachan et al. Nuc. Fus. 2003
L mode(3-4MW)
Type IH mode
10-15MW
- Increase of carbon source depends on scenario (ELMs, recycling flux…) enhanced retention by co-deposition
- Increase by a factor of ~2 of carbon source from L to type I ELMy H-Mode
9Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Implantation and “wall” saturation
- As Tsurf increases Strong outgassing of D, CxDy from target plates (eventually lost of ne control)
- Outgassing signature that implantation is saturated for overheated PFCs
- Also observed on long discharges in TRIAM-1M, Tore Supra. (Sakamoto et al. IAEA 2006, JNM 2007 Grisolia, JNM 1999, ).
Nakano et al. IAEA 2004, Nuc Fus 2006
But, with gas balance analysis this strong outgassing “hides” co-deposition.
And since carbon source increases this enhances retention by co-deposition.
10Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Inventory proportional to duration
30x1021
20
10
0
-10
Wal
l inv
ento
ry (
D)
140120100806040200
Discharge duration (s)
Trapping
Outgassing
Normal discharges Disruption
B Pégourié I-21
- Recent exp. campaign of 10 days on TS repeating the same long pulse (2min – 2MW)
- Total of 5 h of plasma w/o conditioning
Sugiyama et al. Pys. Scrip 2004,Skinner et al, EPS 2001
- Steady state retention and wall inventory proportional to plasma duration - Weak recovery by outgassing and also by disruptions, independently of the
amount retained. DDC in TFTR after DTE (Skinner JNM 1997, 1999) and JET V Philipps P1-63
11Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Retention in carbon devices
Retention by co-deposition dominates
Limit/cancel co-deposition ? High Z
Skinner et al. JNM 1997, 1999 T Nakano et al. JNM 2007
V Mertens et al. EPS 2003 Lasser et al. FED 1999
Long term retention
Cumulative, proportional to pulse
duration and linked to Carbon source
(recycling, ELMs…) JET, JT-60U, AUG, TEXTOR, TS… DT exp on JET and TFTR
Continuous increase of T inventory as the T operations are going on and dominated by co-deposition
TFTRP Andrew et al. FED 1999
12Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom High Z – Alcator C-Mod
D Whyte et al., IAEA 2006
~4x1021D
D Whyte et al. IAEA 2006,B Lipschultz et al., PSI 2008
- 16 repeated pulses (w/o disrp) in cleaned Mo walls - Retained D fluence remains linear with incident D ion
~3.5x1020Ds-1
- Net D wall recovery with planned disruptions
B Lipschultz I-14
- Mo retention proportional pulse duration Implantation? Co-deposition with B?
- Effective D recovery by disruption with Mo as PFCG Wright I-19
13Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom High Z - W in ASDEX Upgrade AUG from “all C” to “all W” (Carbon free)
- With 70% of W the retention was still around 10-20% (C dominated)- 100% W significant drop of retention below 1%
~45% W~70% W
V Mertens et al., EPS 2003, V Rohde et al. EPS 2007
dom. ICRH 2004
100% Ww/o Boronisation
V Rohde P1-61R Dux I-06
14Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom
Where is the fuel retained?
Post mortem analysis
15Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom
Method Principle Quantity measured
SIMSSecondary Ion Mass Spectroscopy
Incident ion flux (Cs+, Ar+, O+) with an angle ~20-30° with respect to the surface
-Analysis of “sputtered” ions +CH3, +CH4… and/or ionised fragments-Depth ~m
RBSRutherford Back Scattering
He+ incident beam (protons) @~1-3MeV)Measurement of the energy of the reflected beam
Analysis of the elemental surface.From nm to mm
TDS
Thermodesorption
Temperature ramp up (room up to 1600K) of a sample.
Under vacuum or inert atmosphere (Mostly Ar or He) w or w/o H2
Total quantity of H, D, O, CxDy …trapped in the material, coupled to Mass Spectrometer
Activation Energy
NRANuclear Reaction Analysis
Nuclear reaction triggered above an energy threshold of the incident 3He beam~1-3MeV 2D(3He,p) 4HeTarget 2D, particle analysed: p, “product” 4He 10Be(3He,p) 12B -- 12C(3He,p) 14N -- 13C(3He,p) 15N
Ratio D/C, Be/CDepth profile1Mev~1.5m2.5MeV ~7.5m
PIGEProton Induced Gamma Emission
13C(p,) N14 Use the narrow resonance for protons at 1.748MeV giving a 9.17MeV gamma ()
Concentration of 13C vs depth Smaller depth resolution, but detection limit ~10 times better than NRA)
NMRNuclear Magnetic Resonance
Resonance frequency proportional to the distance C—H of the element “connected” to H(D)
Used for liquids, in organic chemistry
Post Mortem Analysis
Wide range of methods for different objectives Surface analysis, Structure, Depth profile, Composition…
16Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Where and how ? Implantation in CFCD retained in the samples (by TDS)
EK98DMS780NB31
Comparison with PISCES-A data
No saturation observed for these fluences and 0.5
Test limiter with material stripes exposed in TEXTOR
TEXTOR:
NB
31
ITER
DM
S780
JET
EK
98
Ts = 500K
A.Kreter et al. 2007
J Roth et al. PSI 2006.
Test limiter for dedicated experiments since removed at the end of the experiment; also the case of marker exp (13C)
17Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Where and how ?: co-deposition with C
Dedicated 13C experiment to localize deposition and associated retention
Different Carbon erosion-transport and eventually co-deposition with plasma scenario L and H mode
Also 13C experiments inTEXTOR: P WIenhold et al. JNM 2001, JET: J Likonen et al. FED 2003, AUG: M Mayer et al. JNM 2005,JET: P Coad et al. Nuc. Fus. 2006.
DIII-D: Wamplers et al., JNM 2005, 2007
H-mode NRAL-mode NRAL-mode PIGE
3He,p NRA
18Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom
C-erosion/deposition: JET 2001-2004
Carbon deposition on PFCs
Louvre: 60g (from QMB)
17g
44g
67g
Negligible 19g
24g
Erosion
No clear erosion or deposition
105g 233g
99g
464g
From deposit thickness ( = 1.0 gcm-3 - 1.8 for the
substrate)
-Total C deposition
Inner: 625 g Outer: 507 g
J Likonen P1-70
19Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom
D/C ratios: JET 2001-2004
0.91 0.25
0.15
0.11
0.42
0.02
0.120.08
0.14
0.17 0.79
D/C ratio and retention
Injected : 1800g (5.381x1026D)
In the divertor area
Total D: 66 g = 3.7 % of inj
(2.2x1020Ds-1)
Retention 70% Inner + 30% Outer
J Likonen P1-70
20Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Retention at First wall
(JET – MkII-SRP, 2001-2004)
- Total D retention: 0.3g (0.02%)
- Outer poloidal limiters have a
minor contribution to D retention19μm
0.96 cm3
D/C=0.09
10μm
0.5 cm3
D/C=0.02
0.9μm
0.04cm3
D/C=0.13
3μm
0.2cm3
D/C=0.13J Likonen P1-70
M Mayer et al., PSI 2000, C Brosset et al, PSI 2004, 2006
JET:First wall~200°C
Divertor structure ~50°C
TEXTOR ~8-10% (300°C)Tore Supra ~10-15% (120°C)
~3.8%
- Gap inventory always
connected with C co-deposition
(large in gaps, small in narrow
castellated grooves)
M Rubel et al, JNM 2007
21Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Temperature effect - JT-60U
Masaki IAEA 2006, Hayashi PSI 2006, Sugiyama PSI 2006, Hirohata PSI 2006
Twall= 300°C
6 years – 8h20 of NBI
- Higher Twall lower D/C ratio on PFCs
- No drop of co-deposition in remote area
Twall=150°C
3 years – 2h10 of NBI Long discharges
JT-60U “Normalised” to NBI time (8h20)
- Carbon: inner + dome ~550 g 1.0x1021/sec (2.7 times higher than in JET: 3.7x1020s-1 )
- Carbon: outer erosion ~340 g
210 g comes from the main chamber
PFC D/C~ 0.01-0.15
Remote D/C~ 0.75Same as JET 50°C
Retention ~ 1.3x1020Ds-1
(~8%)
22Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom
2002 – 20034940 s
6A
4
AUG – From all C to all W D inventory
W
C
C
C
C-dominated campaign 2002/2003
Normalised to 3000 s - D on divertor tiles 0.9 – 1.3 g- D below roof baffle 0.4 g
1.3-1.7g
Total D-inventory dominated by inner
divertor and remote areas
Long term inventory ~ 3–4%
M Mayer et al, Nuc Fus 2007
23Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom
20072620 s
6A
4
AUG – all W: Analysed tile D inventory
From C-dominated to all W D inventory reduced ~5-10 Retention<1%
W
W
W
W
M Mayer I-13
Full W camp 2007 – No Boronisation
Norm. to in 3000 s - D on divertor tiles 0.15 – 0.23 g- D below roof baffle 0.03 g
0.18-0.26g (drop ~7-10)
D retention in inner divertor still dominated by C-codeposition: drop ~10-15
D retention in outer divertor dominated by trapping in W – Drop ~5-10
24Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Gas balance – Post mortem
Extrapolation to ITER
Post mortem analysis
- Accuracy of NRA, SIMS… ~ 10%- But cannot include all the PFCs, and effect of oxygen when removed from the vessel…
When analysing the “same plasma” Gas Balance and Post mortem lead to similar evaluation
- Accuracy ~10% for D (H) (Better: He or T)- But CxDy cont., long term outgassing...
Gas Balance
“Global measurement” for “specific” plasma conf. with “minimum” of power/gas
Pin~15-20MW – inj~2-3x1022Ds-1
“Local measurement” integrated over an exp. camp. Reflects the averaged discharge
Pin ~4MW, inj ~4x1021Ds-1
Long term Ret (10-20%) 4-8x1020Ds-1
Retention in the divertor area (MKII-SRP) + Subdivertor (as in JT 60U)Long term Ret 4x1020Ds-1
25Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom
All C reaches tritium limit (700g) in less than 30-40 discharges
All-W reduces tritium problem, but n-effects need to be considered
Fuel inventory estimates for ITER
- More R&D required for evaluation of n-effects:
- Need to improve modeling in retention by co-deposition/trapping (fluence…)
Evaluations based on ion + CX fluxes to the wall and resulting- Implantation- PFC erosion and associated co-deposition
J Roth R-1
Roth PPCF 2008
26Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Summary
Gas balance:
Long term retention for C machine depends on Plasma scenarioAs far as C source exists co-deposition dominates, increases with C production recycling, ELMs (AUG, JET, JT-60U, TFTR, TS) and to pulse duration. Retention by implantation saturates for overheated PFCs (JT-60U) Long term recovery (outgassing and disruption) is weak (TFTR, JET and TS) Mo exhibits retention to plasma duration, but D recovery from disruption. Full W shows a significant drop of the retention ~1%.
Extrapolation to ITER
- A full C machine would reach the limit in “few” discharges of 400s
- A high Z device would limit the co-deposition and strongly reduce retention
Post Mortem analysis Confirms long term retention in PFCs is low but high in remote areas In carbon AUG-JET (3-4%), JT-60U~8%, TEXTOR & TS ~10-15% Significant drop of the retention below 1% in AUG with full W configuration
Complementary and reliable methods retention in full metal wall (ILW)
27Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom
END…
28Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Short term: plasma scenario
ne~0.7nGW
PTOT (MW)NBI+ICRH~13MW
D(in) D (out)
Time (s)
#69260
Ip = 2.0 MA, B = 2.4 T
- Short term retention: “limited” to “fast” reservoir and recovered in between pulses (outgasing)- Long term retention: Co-deposition and implantation : Slow process compared to short term over 5-10 sec.
WELM ~100 kJ ~ 60 Hz
T. Loarer et al., EPS 2007
Heating phase
Injection
Exhausted
Retention
29Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Retention in gaps
2 decay lengths in TFTR1~2mm hydrogen rich deposition ((D+T)/C~0.2
prompt redeposition of C2Dx (1,3,5) ... with high
sticking coefficient 2~6-12mm influenced by the gap width (up to
30mm with large gaps) migration of neutral hydrocarbon with low sticking coefficient
T Tanabe et al. Fus Sci and Tech 2005
0
3
6
9
12
15
18
0 3 6 9 12 15
Distance from Plasma [mm]
D a
nd
C [
e17/
cm2]
]
D, Side A
D, Side B
C, Side A
C, Side B
JET Be Limiter Tiles
- D deposition in the castellation always associated with Carbon.- Short decay length of deposition in the castellation: = 1.5 mm.-D content in the castellated groove does not exceed 8 x 1017 cm-2.- No deuterium detected in bulk beryllium.
M. Rubel et al.
TFTR
30Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Retention in gaps
M Rubel et al, JNM 2007
Be limiter tiles of Mk-I divertor
Distribution of D on side surface in the gaps between the Mk-I CFC tiles.
31Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Gas Balance: Accuracy
DT experiments in JET…over the first week the most difficult part to evaluate is the outgassing. In actual tokamak discharges.
Loarer JNM 2005
2.5x1024
2.0
1.5
1.0
0.5
0.0
e-
41800417604172041680Pulse number
Cumul T injected T retained at the end of the pulse PTE1 : Model Regenerated by cryopump Cumul T Outgased Net T Retained
Total of 11.743 g
50-50 % D-T
100% T 100% D
Max of 7.811 g
Max of 5.115 g
65% of retention during the pulses (~10sec)
40% of retention over the campaign
17% after intensive cleaning (~6 months)
T particle balances from Gas balance analysis Good agreement between gas balance and cryopump reg. (green points)
32Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom JET DTE Campaign
JET DTE Campaign
1997-1998T Vessel inventory
End of DTE1 campaign
Injected-Exhausted
(35g – 23.5g)
11.5 g
Clean up phase (D, H, He, Disrp, GDC…)
Remove 5.3g
6.2 g
Venting
Remove 2.5g
3.7 g
Flakes
Remove 0.5g
3.2 g
Inner and Outer wall
Remove 0.1g
3.1 g
480 Tiles of Divertor
Remove 0.1g
3.0 g still remaining (flakes)
After the campaign and intense cleaning campaign (pulses, conditioning, venting, the T inventory in the PFCs is “negligible”
(~0.2 g). Trapped tritium in flakes. Bekris et al. JNM 2005
33Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom JETand TFTR DTE Campaign
Skinner et al. EPS 2001
4.2g2.06g
Drop by a factor of ~2 in 11/2 year
34Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom High Z material: Alcator C-Mod
Wampler, IEEE 1999, PSI 1998
- OSP (net erosion): low D retention consistent with results from Mo erosion and B deposition.
-ISP Boron coverage is very small whilst D content is also very small
- Boron surface layers from boronisation was found at all locations except near the OSP
Dominant impurity: Boron and “some” amount of Mo
35Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Gas balance: AUG - All W
V Rohde et al. this conf. P1-61
Gas balance divided in 3 phases- Limiter- Ramp up- Steady State Long term
Carbon PFC
W Main Chber
All W
36Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom DTE: TFTR and JET
C Skinner et al. 2002
Effect of oxygen on samples removed from device
37Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom DTE: TFTR
C Skinner et al. 2002
38Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Location of TFTR tritium inventory
C Skinner et al. 2002
39Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom Co-deposition and Carbon production
- Increase of carbon source (ELMs, recycling flux…)
enhanced retention by co-deposition
Non-linear carbon deposition on ELM energy
Thermal decomposition of surface layers
1
3
4
QM
BA Kreter, G Esser et al sub PRL
A Kreter I-03
40Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom High Z exp in Alcator C-Mod
B Liptschultz I-14
- Although cleaning process allows to remove the boron layers, there is still a non negligible amount of boron at the surface
- If experiments are carried out in AUG with full W and boronisation, this could clarify the possible effect of boron in the retention behaviour observed in Alcator C-Mod
41Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo
Euratom
One possible explanation are plasma impurities, largely B (~1 %), that are present in the C-Mod plasma and in the first 500 nm Mo tiles.
Overall, in both high-Z devices the campaign integrated retention on D is small, much smaller than for carbon or boron co-deposition.
Alcator C-Mod and ASDEX Upgrade
Alcator C-mod, Mo ASDEX Upgrade, W
Gas balance Variation between net outgassing and up to 50% retention, linear with number of discharges
~1% retention,
Post-mortem
≤ 1 % < 0.2 % retention(to be confirmed)
Modelling 1-2 % retention, linear with number of discharges
Roth R-1