Prsentation PowerPoint

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Report of the SEWG on Gas balance and Fuel
retention
T Loarer with contributions from S Brezinsek, C
Brosset, G Esser, J Likonen, M Mayer, Ph Morgan,
B Pegourie, V Philipps, V Rohde, J Roth, M Rubel,
J Strachan, E Tsitrone EU TF on PWI and JET
EFDA contributors
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Outline and objectives of the SEWG (2008)

• Gas balance analysis (plasma operation)
• Experiments performed to built a reference data
  base in Carbon in JET? Understanding DT results
  (97-98) and quantify the benefit (?) in Be/W
• QMBs to assess the contribution of the ELMs on
  erosion-retention
• AUG? Gas balance in pure W (prior to
  boronisation)
• Post mortem analysis
• Laser desorption in TEXTOR to quantify locally
  the retention
• JET ? Completion of the MKII-SRP divertor
  retention and deposition on mirrors
• Tore Supra ? Progress on tile analysis and
  comparison with gas balance
• AUG ? From Carbon to full Tungsten

• Overall objective
• Understand and evaluate how much T retained,
  where (role of the material).

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Built a reference data base in Carbon

• Repetitive pulses to avoid history effects
• Regeneration of divertor cryopump before and
  after session
• Long Term retention
• Injected Regenerated
• (regeneration about 60 min after last shot)

• Repeat the pulses in Be/W to quantify the benefit
  (?) on the retention

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Impact of limiter phase

• Mode D standard X-point (9s of limiter
  start-up phase) 70534
• - Mode B Early X-point (1.3s of limiter
  start-up phase) 73654
• Except the limiter phase ? Comparable plasma
  parameters
• Ip, BT, ne, ICRH, Gas rate, recycling

Ip/BT2.0MA/2.4T, 1.8MW ICRH only
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Retention in L and H-mode

• Impact of the limiter phase in the fuel retention
  experiments with an early X-point (1.2s of
  limiter phase) and late X-point formation (8-10
  s of limiter phase) is moderate. Normalisation
  Divertor vs. Heating time
• Retention closely linked to the carbon source

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Carbon production and scenario
J Strachan et al. Nuc. Fus. 2003
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G Esser et al.,
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DT experiments in JET

• Retention by implantation and co-deposition

D TFTR

Same retention although different scenario
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Implantation and co-deposition
Injection
Retention deduced from Cryo regeneration
JET DT experiments - Implantation dominates in
phase 1 (L mode) - Co-deposition main process
in phase 2 (High power H mode)
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 Pure  W w/o boronisation
V Rohde et al.,
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• Carbon (blue and pink)
• No wall saturation
• 20 retained after pulse
• Up to 10 removed by HeGD and day scale
  outgassing
• Good agreement with probes

• Tungsten (Green and red)
• Wall saturation reached
• No gas retained within error bars
• Up to 10 removed by HeGD and day scale
  outgassing
• Good agreement with probes

V Rohde et al.,
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Outline and objectives of the SEWG (2008)

• Gas balance analysis (plasma operation)
• Experiments performed to built a reference data
  base in Carbon in JET? Understanding DT results
  (97-98) and quantify the benefit (?) in Be/W
• QMBs to assess the contribution of the ELMs on
  erosion-retention
• AUG? Gas balance in pure W (prior to
  boronisation)
• Post mortem analysis
• Laser desorption in TEXTOR to quantify locally
  the retention
• JET ? Completion of the MKII-SRP divertor
  retention and deposition on mirrors
• Tore Supra ? Progress on tile analysis and
  comparison with gas balance
• AUG ? From Carbon to full Tungsten

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Laser desorption on ALT limiter tile
? Analysis of fuel retention in carbon materials
and deposits
Deposition
Erosion
ALT limiter tile Exposed 2004- 2008 Total shots
8534, 43473 s (12h)
V Philipps et al.,
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Laser desorption on ALT limiter tile
6 x1021 H,D/m2
Retention,erosion area 4-6 1017D/cm2
total 8.5 x 1019 D/tile Deposition area
up to 3-1919D/cm2 5 x 1020
D/tile 228 tiles 1.4 1023 H,D 0.3g H,D
Significant fuel retention in erosion areas (4-6
1021/m2 at fluencies of 2-4 1026H,D/m2 and temp.
of 150- 250C , (somewhat underestimated in past
analysis)
V Philipps et al.,
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Toroidal distribution of D on ALT-II Limiters
from TEXTOR
Analysis of 8 tiles from the ALT-II belt pump
limiter 14100 s (4h00)
Aim To check toroidal uniformity of deposition
and retention.

• Main Results
• Deposition pattern is the same on all analysed
  tiles.
• Carbon-rich co-deposits contain 8-10 of
  deuterium and around 10 B.
• Other impurities Si, Ni, Cr, Fe, Mo and traces
  of W, Hf, Ti.
• Layer thickness in the deposition zone 40 50 mm
  as checked with SEM for the detached flakes.

M Rubel et al.,
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Co-deposits on metal mirrors (Mo and steel)
M Rubel et al.,
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D/C ratio and retention
D/C ratios JET 2001-2004
0.02
0.14

• Injected 1800g (5.381x1026D)
• In the divertor area
• Total D 66 g 3.7 of Ginj
• (2.2x1020Ds-1)
• Retention 70 Inner 30 Outer

0.42
0.11
0.15
0.91
0.25
0.12
0.08
0.17
0.79
J Likonen et al
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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
retention
J Likonen et al
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Experimental campaign Tore Supra

• Carbonisation (13C) boronisation ? markers

• Repetitive long pulses (2 minutes) ? load the
  vessel walls with D

• 5 hours of plasma w/o conditionning (1 year of
  operation in 2 weeks)
• ? pre-campaign inventory x 4

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40 Tiles extracted for analysis
DITS CFC structure PFCs IR Detritiation

• ? 10 tiles selected out of 40
• 5 erosion zone
• 2 thin deposits
• 3 thick deposits

B Pegourie et al.,
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Tile analysis NRA average D/C profiles
Erosion zone 200C
Thin deposits 120C
Thick deposits 500-600C (up to 1000C close to
the tangency point)
Gaps lt 400C
Poloidal gaps
Top of the tiles
B Pegourie et al.,
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Tile analysis Thermodesorption
2g/m2
0.4g/m2
B Pegourie et al.,
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D-inventory effect of time
Decrease of the D-content between end of
operation and analysis
Estimated TPL D-inventory at the end of plasma
operation 7.2 g if CFC and deposits concerned
(70 of total) 5.4 g if only CFC concerned
(55 of total)
B Pegourie et al.,
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DITS Gas balance and post mortem
B Pegourie et al.,
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Deuterium inventory in AUG From C to W
4940 s
C-dominated campaign 2002/2003 D on divertor
tiles 0.9 1.3 g D below roof baffle 0.4
g in 3000 s
M Mayer et al.,
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AUG divertor Evolution of D inventory

• Carbon dominated machine
• Total D-inventory dominated by inner divertor
  and remote areas

• All-W machine
• Boronizations result in high D-inventory,
  co-deposition with B (2005/2006 campaign)
• D-inventory dominated by trapping in
  VPS-layers at outer strike point
• Decrease of total D-inventory by factor 5 10
  from C-dominated to all-W

M Mayer et al.,
M Mayer et al.,
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Fuel retention studies in MAST

• Fuel retention studies will focus on gas balance
  calculations in the near-term
• supported by a detailed interpretive modelling
  effort
• full Langmuir probe and Da measurements, soon
• maybe some campaign-averaged post-mortem
  analysis during the next engineering break

• Plans for post-mortem analysis of well
  characterised samples, but only preliminary
  work in 2009
• Divertor Science Facility, midplane materials
  probe

S Lisgo et al.,
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Summary

• Gas balance
• Long term retention for C machine depends on
  Plasma scenario
• As far as C source exists ? co-deposition
  dominates, increases with C production recycling,
  ELMs (AUG, JET, TFTR, TS) and a to pulse
  duration.
• Carbon machine ? Dominated by co-deposition
  divertor and limiter machines and associated to
  erosion (Scenario, ELMs)
• Full W shows a significant drop of the retention
  1.

• Post Mortem analysis
• Evaluation of the retention by laser
  desorption?Retention in erosion area not
  negligible ? TEXTOR and TS (DITS)
• In carbon? AUG-JET (3-4 in the divertor area)
• Significant drop of the retention below 1 in
  AUG with full W configuration
• Effect of time can be significant (up to factor
  of 2)

• Gas balance and post-mortem are Complementary
  and reliable methods
• Results are consistent ? DITS project and DT
  experiments at JET!
• ? Both methods are necessary to know where and
  how to remove the tritium?

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EU-PWI SEWG RETENTION, JULY 2008 INTERPRETIVE
MODELAttempt to fold in post-mortem analysis of
well characterised samples

• Divertor Science Facility (DSF) ? big name,
  little probe (3x3 cm)
• vacuum-lock probe system commissioned by end of
  2008, with luck
• need to develop a good scenario so that a
  significant fluence can be built-up ? quasi
  stationary strike-point, no disruptions
• perhaps only local transport studies, i.e. no
  input to global retention picture
• can also expose samples on an existing outer
  midplane probe system

TESTS OF MOCK-UP PROBE HEAD AND SHAFT
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Post mortem sample cutting
TDS top gaps
TDS no gaps
10 tiles ? 7 standard 3 refined cutting (1 in
each zone)
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Post mortem sample extraction

• First analysis campaign 10 tiles
• 5 in erosion zone
• 2 in thin deposits (plasma loaded LFS and
  shadowed)
• 3 in thick deposits

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Integrated D-inventory
NRA (top lateral faces)
TDS (top) NRA (lateral)
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D-inventory effect of time
Decrease of the D-content between end of
operation and analysis
Estimated TPL D-inventory at the end of plasma
operation 7.2 g if CFC and deposits concerned
(70 of total) 5.4 g if only CFC concerned
(55 of total)
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Carbon deposition on PFCs
C-erosion/deposition JET 2001-2004

• From deposit thickness
• (r 1.0 gcm-3 - 1.8 for the substrate)
• Total C deposition
• Inner 625 g Outer 507 g

J Likonen et al
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Confocal microscopy ongoing work
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A3 exposed finger
Erosion zones evidenced
A3 A4 A5 A6 A7
A4 new finger
A5 new finger !
A6 new finger
T7 T6 T5 T4 T3
T2 T1
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PFCs cleaning after the DITS campaign

• Deposits formed of successive layers
• variable toughness, roughness, density

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Cleaning the gaps
Deposits in gaps between tiles and fingers mainly
in erosion zone
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Scraped deposits
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Tentative C balance (2002-2007)
1000 g (confocal)
Modelling (BBQ) gross erosion 2000
g Suggests low redeposition (50- 60) Refined
modelling estimates from spectro. ongoing
TPL redeposition 145 g (scraping) net erosion
1000 g (confocal)
Bumpers etc redeposition 645 g (scraping)
net erosion missing (glow ?)
Global redeposition 800 g (scraping)
net erosion 1000 g (confocal)
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M4 D2
Examples of data analysis
Mass 19 mainly CD3H
Valves closed before laser shot, recording of all
masses, automatic fit procedure to evaluate mass
signal increase and total hydrogen gas release,
only deuterated species are taken into account
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Poloidal direction (mm)
Additional desorption in second shot from edges
of laser spot, but lt 5 No increased desorption
by increasing laser pulse lengths ( 1.5 ? 3 ms)
and reducing the power by v2 (same surface
temperature, v2 deeper heat propagation ) Maximum
thickness of ALT deposit to be determined,
estimated to about 30 ?m
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Retention in erosion dominated areas
New data points Include long TEXTOR operation
history!
Particle fluence from H? spectroscopy under
evaluation Estimated value (using similar data
from other campaigns) 2 x10 26 H,D /m2
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Type I ELMy H-mode
Ip 2.0 MA, Bj 2.4 T
69260
PTOT (MW) NBIICRH13MW
DWELM 100 kJ 60 Hz
Da (in)
Da (out)

Time (s)
- 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
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High power discharge in JET
Gas balance on line, w/o regeneration
Ip3.5MA, BT3.2T
ne
Ptot (NBI ICRH) 23-24MW
Wdia9.5MJ
Gas 5.0x1022Ds-1
ELMs?600-700kJ per ELM
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Gas balance High power discharge

• Using the same pumping speed ? Retention as high
  as 3.3x1022Ds-1
• Consistent with strong carbon erosion from
  recycling and ELMs
• Increase by 10 of the retention? To be
  confirmed by dedicated exp

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C source for High power discharge
Type I ELMs (600-700kJ)
Type I ELMs (100kJ)
L mode
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Implantation
- JET 200 m2 maximum retained fluence
1021m-2 ? reservoir of 2 1023 T ? consistent
with implantation of particles with incident
energy of 200eV.
JET DT experiments - Implantation dominates in
phase 1 - Co-deposition main process in phase 2
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Carbon production and scenario
J Strachan et al. PSI 2008
Carbon ionisation rate in the SOL as a function
of D ionisation rate
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Deuterium in different carbon materials
NRA spectrum and depth profile for NB41 exposed
in PISCES-A ? 3?1025 D/m2 at Ts 470 K
Experimental set-up (test limiter) at TEXTOR to
study deposition and in-depth D migration into
materials
VR, FZJ, SFA, PISCES
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Co-deposits on metal mirrors (Mo and steel) at JET
General tendency On all divertor mirrors
deposition decreases with the depth in
channel. On the wall mirrors deposition increases
with the depth in channel.
Other results All co-deposits contain C-12, D
and small quantities of Be and 13C. In many
cases, layers are thicker than the information
depth with IBA.
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