1 th loarergas balance and fuel retention – eu tf on pwi – 29 october 2007 madrid th loarer with...
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1Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Th Loarerwith contributions from
D Borodin, C Brosset, J Bucalossi, S Droste, G Esser, G Haas, A Herrmann, A Kirscher, A Kreter, K Krieger, J Likonen, A Litnovsky, M Mayer, V Mertens,
Ph Morgan, V Philipps, G Ramos, S Richter, V Rohde, J Roth, M Rubel, A Sergienko, E Tsitrone, E Vainonen-Ahlgren, P Wienhold,
EU TF on PWI and JET EFDA contributors
Gas balance and Fuel retention
- Overview of “Gas balance and fuel retention” results
Tokamak experiments (JET, TS, AUG, TEXTOR)
Post mortem analysis (Laboratories)
- Summary and further plans
Euratom
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2Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Introduction
- Evaluation of hydrogenic retention in present tokamaks is of high priority to
establish a database for ITER (400 sec ~ 7min…10-20 sec 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
mobilisable T-limit (350 g) in 35 pulses.
- Retention rates of this order (~10-20%) or higher are regularly found using gas balance in C-wall tokamaks.
- Retention rate ~5 times lower are obtained using post mortem analysis
- Are these two methods reliable to evaluate the retention and is it possible to understand why they lead to different results ?
- SEWG to clarify Gas Balance vs post mortem analysis
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3Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
physics: material erosion, migration & fuel retention
• QMB measurements
• Spectroscopy
• Gas balance measurements
• Deposition probes
• 13C migration
• Post mortem tile analysis
D,T
Mechanisms for fuel retention
Two basic mechanisms for
Long term fuel retention
Deep Implantation, Diffusion/Migration,
Trapping
C, Be C, Be, D ,T
In carbon wall devices codeposition dominates retention (also expected for Be wall conditions, JET ILW, ITER)
Codeposition
Short term retention (Adsorption: dynamic retention)
Recovered by outgasing in between discharges
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4Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Calibrated Particle Source
(Gas, NBI…)
Divertor cryo-pumps
Wall Retention
Long & Short Term
Particle balance procedure on JETRepeat sets of identical discharges (no intershot conditioning)
Plasma
Injection = Pumped + Short Term Ret + Long Term Ret
Total recovered from cryo-regeneration: Pumped + intershot outgassing over ~800s (assumed equal to Short Term Ret )
Regenerate cryopumps before and after expt. collect total pumped gas (accuracy~1.2%)
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5Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Particle fluxes: H mode Type I
From L mode to Type I ELM H-mode Increase of long term retention- with the recycling flux- with ELMs Energy
Ip=2.0MA, BT=2.4T
13MW NBI+ICRH ELM Energy~100kJ
@16 sec,
Ret~5.2x1021Ds-1
LongRet ~ ShortRet
@20 sec,
Ret~2.9x1021Ds-1
LongRet >>ShortRet
Injection
Pumped flux
Retention
Long Term Ret
Th Loarer et al
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6Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Integrated particle fluxes
Hα
CIIIType I ELMs
Type III ELMs
L mode
L mode
Type I ELMs
Type III ELMs
Integrated CIII and Hα horizontal light
(L-mode, Type III and Type I ELMs)
- Slope for Type I ELMy H-mode shows both enhanced recycling and total carbon source.
Higher recycling and ELM Enhanced carbon erosion and transport leading to stronger carbon deposition and fuel codeposition
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7Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
ELM induced C deposition
Non-linear dependence of carbon erosion on ELM energy
thermal decomposition of surface layers and favourable geometry rapidly increases QMB deposition
1
3
4
QM
B
Can explains high deposition rates on water-cooled louvres during 97-98 JET DT experiments high T-retention
A Kreter, G Esser et al
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8Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Particle Balance summary on JET
- Long term retention increases from L-mode to H-mode
Increased C erosion and transport due to increased recycling and effect of ELMs enhanced C erosion enhanced co-deposition and retention.
- Recovery between pulses (short term retention) always constant within a factor ~2 – in the range 1-31022D
Independent of discharge type, ELM energy, quantity of injected particles
Pulse type
Heating phase (s)
Divertor phase (s)
Injection(Ds-1)
Long term retention (Ds-1)
ret/inj
L-mode 81 126 ~1.81022 1.741021 ~10%
Type III 221 350 ~0.61022 1.311021 ~20%
Type I 32 50 ~1.71022 2.831021 ~17%
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9Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Tore Supra: the DITS project
Objectives : • Clarify post mortem analysis vs Gas Balance• Retention mechanisms (codeposition vs bulk migration)
(Deuterium Inventory in Tore supra)
3 phases : • dedicated experimental campaign Gas Balance• dismantling of a sector of the limiter samples for post mortem analysis• sample analysis (collaboration with european labs, EU PWI TF)
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10Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Scenario of the DITS campaign
Main issue : UFOs (C + metals + D ? ) detachment disruptions
scenario at lower LH power (< 1.8 MW) + slow ramp up
- No evolution for C - Fe and O level increasing to values before carbo/boronisation
Scenario 2 (lower power ~ 80 s)
Scenario 1 (nominal – 120 s)
Repetitive pulses every 20 mn (~ 40 mn of plasma each day)
5 h of plasma w/o conditionning
scenario at lower LH power (< 1.8 MW) + slow ramp up
Scenario 2 (lower power ~ 80 s)
scenario at lower LH power (< 1.8 MW) + slow ramp up
Scenario 2 (lower power ~ 80 s)
E Tsitrone et al
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11Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
UFOs on CCD imaging of the TPL
E Tsitrone et al
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12Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
1st scenario : PLH = 2 MW 2nd scenario : PLH = 1.6-1.8 MW
No wall saturation observed after 5h00
E Tsitrone et al
Injected ~ 5.8x1024D (19.5 g)
Trapped ~3.3x1024D (11 g)
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13Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Inventory proportional to discharge duration
Disch. OK
Disruptions
Outgassing
Trapping
E Tsitrone et al
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14Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Total exhausted = (6×10-5 Pa) × (1.3×106 s) × 10 m3/s ~ 700 Pa.m3/s ~ 3.5×1023 D atomsto be compared to WI ~ 3.3×1024 D atoms (~ 10 %)(upper limit : D2 concentration in pumped gas decreases rapidly)
Long term recovery << wall inventory
E Tsitrone et al
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15Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Summary
DITS experimental campaign : successfully completed• 13C carbonisation / 11B boronisation performed• 5h of plasma w/o conditionning : 1 year of operation in 2 weeks• Reliable operation (LH, cooling loops, PFCs)• Main limit : UFOs disruptions operational limit ?• 80 % of the objective reached (WI = 3.3 1024 D or ~11g) : ok for qualitative and quantitative analysis
Particle balance• No wall saturation, retention proportional to discharge duration. • Exhausted gas dominated by D during the shots• Disruptions at low Ip, long term recovery : negligible in the balance
DITS project on tracks : TPL sector dismantled, selected fingers extracted samples available for analysis ~ november 2007
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16Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Phases of discharges observed in C
Typical discharge “puff and pump” steady phase reached after ~2sec
V Rohde et al.
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17Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Full W configuration: “Carbon free” machine, How does it compare to C in terms of fuel retention ?
In typical discharge “puff and pump” steady phase not reached
V Rohde et al.
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18Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Gas balance with W wall
Wall loading observed, no steady state reachedV Rohde et al.
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19Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Gas Balance summary from AUG in “W”
-Gas Balance is needed to verify the benefit of full tungsten wall.
-Support from EU TF on PWI to investigate gas balance, but support more
difficult from man power point of view.
-However, experiments performed and detailed analysis to start soon.
-Data set exits, but direct comparison with C is very difficult due to different
plasma scenario.
-Accuracy is dominated by pumping of cryo pump.
- Due to the high gas puffing rate (>1022Ds-1), an accuracy of ~1% is required
in AUG. Improvement of the accuracy by adding a separated volume to
store all the gas (as in AGHS in JET)
V Rohde et al.
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20Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Deuterium retention in CFCDeuterium retained in the samples (by TDS)
EK98DMS780NB31
Comparison with PISCES-A data (J.Roth PSI 06)
Retention in both CFCs slightly higher than in EK98Good agreement with N11 exposed in PISCES-A
No saturation observed for obtained fluencesFuel retention in TEXTOR is dominated by co-deposition (Contribution of in-bulk retention to total retention ~10%)
Photograph of the test limiter with material stripes exposed in TEXTOR
NB
31
ITER
DM
S780
JET
EK
98 TEXTOR:
Ts = 500K
A.Kreter et al.
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21Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Toroidal direction
Poloidal direction
SOL Plasma
Shaped cells
10x10x12(15)mm
Rectangular cells
10x10x15 mm
The shape of a castellation cells can be optimized to reduce impurity and fuel transport into gaps
2 shapes of castellation studied
Experimental details
● Shaped and rectangular cells
exposed under the same plasma
conditions
● 16 repetitive discharges:
112 sec, Te~20eV, ne~6x1018m-3
•Fluence averaged over plasma—wetted area:•Rectangular cells: 2.2*1020 D/cm2
•Shaped cells: 4.2*1020 D/cm2
● Post-exposure analyses with
SIMS, Dektak, NRA and EPMA
on all sides of poloidal and
toroidal gaps.
Gaps 0.5 mm
Exposure of W castellated limiter in the SOL of TEXTOR
20o
Toroidal gaps
Poloidal gaps
A. Litnovsky
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22Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
0 2 4 6 8 10 120
20
40
60
80
100
120
140
160
0.1
1
10
0 2 4 6 8 10 12 140
20
40
60
80
100
120
140
160
0.1
1
10
●Toroidal gaps exposed deep in plasma
Fuel accumulation in toroidal gaps
Shaped geometry Rectangular geometry
D/C (%)
NС, *1016 at./cm2
ND, *1014 at./cm2
D/C (%)NC, ND
D/C (%)
NС, *1016 at./cm2
ND, *1015 at./cm2
D/C (%)NC, ND
Distance from the top of a gap, mm
Plasma-closest edge
Less fuel in gaps of shaped cells
Distance from the top of a gap, mm
Plasma-closest edgeDΣ=1.46×1015 at/cm2 DΣ=3.46×1015 at/cm2
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23Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
●Poloidal gaps
Different fuel retention in the poloidal and toroidal gaps
Plasma flow
open sideshadowed sidePlasma-
Ongoing research: short summary
More fuel retention in plasma-shadowed sides;
2-3 times more fuel stored in gaps of shaped cells*;
●Toroidal gaps
At least 2 times less fuel stored in gaps of shaped cells exposed deeper in
plasma;
Independently on shaping, at least 2 times more fuel stored in the toroidal gaps
exposed further away from plasma;
Still less fuel in gaps of shaped cells exposed further away from plasma,
although the difference is around 50%.
A. Litnovsky et al., Phys. Scr. T 128 (2007) 45;
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24Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Be toroidal belt limiter
Operation: 1989 – 1992
56 000 s of plasma (~16 hours)
2000 castellated blocks.
Studies performed with Ion Beam Analysis on two tiles:• Castellated grooves: both sides of 6 grooves;• Side surface between the tiles; • Top surfaces of tiles.
Deposition and Fuel Inventory in Castellated Beryllium Limiters from JET
Be
Be
Be
M. Rubel et al
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25Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Top and Side Surfaces of Cleaved Beryllium Limiter Tiles
Cleaved limiter blocks mounted in the chamber for IBA
• Bridging of some gaps by molten Be.• Grooves are not filled with Be.
M. Rubel et al.
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26Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Deposition in the Castellated Grooves of the Beryllium Limiter Tiles
Side A Side B
Surfaces in thecastellated groove
Freshly cleavedsurface
Freshly cleavedsurface
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
Messages:
• Deuterium deposition in the castellation is 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.
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27Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
10μm
7μm
72μm
44cm3
67cm3
99cm3
105cm3
233cm3 17cm3
464cm3
26μm
10μm
38μm
33μm
41μm
19cm3
24cm3
60g on louvre
18μm 300μm 32μm
Thicknesses: surface analysesVolumes: integration over torus
130μm
200μm 22μm
Deposition at divertor (MkIISRP, 2001-2004)
J Likonen et al
- Carbon: inner total 625 g (1.0 g/cm3)
=3.1x1025 C-atoms = 3.7x1020/sec, D/C from NRA → 30g D
Injected D: 1800g, retention fraction: 1.7%
- Carbon: outer 507 g = 2.5x1025 C= 3.1x1020/sec
Deuterium: D/C from NRA → 13 g
retention fraction: 0.7%
Total D retention: 43 g = 2.4 % of injected
No SRP included
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28Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
J Likonen et al
Deposition at OPL and IWGL (MkIISRP, 2001-2004)
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29Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
J Likonen et al
Conclusion for MkIISRP, 2001-2004
- Deposition at divertor very asymmetric (70% inner divertor, 30% at the outer)
- Main D retention at divertor
- OPL limiters have minor contribution to D retention
- IWGL have most likely a small contribution
- D retention: 10% (MkIIA), 4% (MkIIGB), 3% (MkIISRP, SRP analysis under way)
- Long term fuel retention: 13% (TFTR), 8% (TEXTOR), 5% (DIII-D) and 4% (AUG with C)
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30Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
AUG Wall areas and analysis methods
innerheatshield
upperdivertor
upperPSL
lowerPSL
pump duct
innerdivertor
roofbaffle
outerdivertor
ICRHlimiter
Analysis methods
• NRA D(3He,p) - 1000 keV: D inventory in 2 µm - 2500 keV: D inventory in 10 µm
• Marker stripes for RBS - Deposition of B, C (talk on 9.5.2007)
• SIMS
Data for 2002-2003 and 2004-2005
Campaigns Carbon dominated machine
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31Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Deuterium retention in 2002–2003
Long-term D retention 3–4% of fuelling
Majority on divertor tiles (50-60%), followed by remote areas (20%)
Retention Fuelling
from (B+C),assumingD/(B+C)=0.4
Gas balance (V Mertens 2003): 10–20%Marginal agreement, taking error bars into account
M Mayer et al, Nuc Fus 2007
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32Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
• Exposed for 2 campaigns 2003 – 2005
about 7000 plasma seconds
• Thin W-coating with 4 µm thickness
using PVD
6A
6B
5
4
9A
9B
9C
1low
1up
2
3A
3B
WC
10
M Mayer et al
•Surface temperature close to RT,
with maximum of 500 K
•D/W = 20 – 30% at surface:
trapping with C: 2–4×1021 C/m2
•D/W = 0.01 – 0.1% in W-layer
0 1 2 3 4 5 6 710-3
10-2
10-1
100
101
Depth [m]
D in PVD-W (ASDEX UG)
D c
on
cen
tra
tion
[a
t.%
] position #1 position #5
QD(pos. 1) = 1.33x1021 D/m2
QD(pos. 5) = 1.69x1021 D/m2
Tungsten machinePreliminary resultsAnalysed tile for D inventory
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33Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Evaluation of the total amount of D retained in W
D-inventory: 1.5×1021 D/m2
AUG wall area: 72 m2
1×1023 D-atoms = 0.3 g
D-input in 2 campaigns: 160 g
Retention with W-walls: < 0.2% of input
(Retention with C-walls ~ 4% of input)
M Mayer et al
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34Th Loarer Gas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid
Summary & Comparison Gas balance-Post mortem
- Post mortem analysis confirm that the long term retention in the PFCs is low.
AUG (~4% in C, less in W), JET (~3-4%), TEXTOR and TS (DITS) ~8%- Post mortem analysis is representative of the averaged over a campaign of a small area (difficult for extrapolation: flakes in JET during DTE ): cumulative effects of thermal release (plasma ops.), GDC, disruptions, ….. (eg JET Averaged power with MkIIGB~4MW, and averaged fuel rate ~5x1021Ds-1 in 2007)- Retention in PFCs, mainly in the divertor (30% Outer leg/ 70% inner leg)
- Retention in gaps always associated to carbon, typical length ~4mm
Gas balance: Long term retention evaluated in the range 10-20% for carbon machine.Analysis generally carried out for plasma conditions different from averaged Retention increases with recycling (gas/NBI injection) and the ELMs (Type III to Type I)
eg “interesting pulse”~5 times the average” JET ~15-20MW, and fuel rate ~2.5x1022Ds-1
Long term recovery between pulses is negligible in the overall balance
Gas balance or Post mortem analysis: Carbon leads to high retention
Further results and experiments (main)
- AUG: analysis of the retention in a full W machine answer to the question of C
- Tore Supra: DITS project Where is the D trapped ? In the carbon structure ?
- JET: Preparation of the ILW (no carbon), reference pulses to be quantify in Carbon
- Complementary experiments of post mortem analysis