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
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
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
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%)
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
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
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
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%
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)
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
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
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)
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
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
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
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.
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.
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.
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.
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.
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
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
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;
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
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.
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.
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
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)
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)
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
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
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
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
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
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