1 th loarergas balance and fuel retention – eu tf on pwi – 13 november 2006 th loarer with...

1Th Loarer Gas balance and fuel retention – EU TF on PWI – 13 November 2006

Th Loarerwith contributions from

C. Brosset1, J. Bucalossi1, P Coad2, G Esser3, J. Hogan4, J Likonen5, M Mayer6, Ph Morgan2, V Philipps3, V. Rohde6, J Roth6, M Rubel7, E

Tsitrone1 , A Widdowson2, EU TF on PWI and JET EFDA contributors

Gas balance and Fuel retention

1) Association EURATOM-CEA, CEA-Cadarache,13108 St Paul lez Durance, France.2) Culham Science Centre, EURATOM-UKAEA Fusion Association, OX14 3DB, UK3) Institute of Plasma Physics, Association EURATOM-FZJ, 52425 Jülich, Germany4) Oak Ridge National Laboratory, Fusion Energy Division, TN37831-8072, USA5) Association EURATOM-TEKES, VTT Processes, PO Box 1608, 02044 VTT Espoo, Finland.6) Max-Planck IPP-EURATOM Association, Garching, Germany7) Alfven Laboratory, Royal Institute of Technology, Association EURATOM-VR, Stockholm, Sweeden

Outline:Gas balance and fuel retention

During a pulse, after/between pulses Integrated over a day, a week and a full campaign Fuel retention mechanisms

Summary and further plans

TECEuratom


- Evaluation of the hydrogenic retention in present tokamaks is of crucial

importance for the long discharges foreseen in ITER (400 sec ~ 7min).

- A retention of 5% of the T injected would lead to the limit of 350g (working

guideline for initial operation) in 70 pulses (1% ~1g).

- In the EU TF on PWI, SWEG to study gas balance and fuel retention, to assess

the processes of the fuel retention and to extrapolate to ITER.

- SWEG meeting on gas balance and fuel retention at JET 11 and 12 July 2006

INTRODUCTION

Results from different test beds and tokamaks

Limiter and Divertor devices in EU:

ASDEX Upgrade, JET, TEXTOR, Tore Supra, but also

from Alcator-C, JT-60U, Triam


Retention during pulse

Significant retention unless :• Low fuelling rate (Long L mode in JET)

• No influence of W observed between 2003 and 2005

in AUG (45 to 80% of W coverage)• No influence of ELMs observed so far (W and/or C)

Phase 2 : ~ constant retention rate Always a significant fraction of the injected flux (20-50%), but small fraction of the recycling flux (1-5%)

Phase 2

Low fuelling

AUG

Common features on all devices :

Phase 1 : decreasing retention rate~ 1 to 50-100 sMachine (Limiter/Divertor), Scenario Conditioning and Material (Be - C – W)…

5

4

3

2

1

0

102

0 Ds-1

4003002001000

Time (s)

# 32299 # 32300

Phase 1

TS


Also observed on JT-60U…ne~0.65 nGW

Low fueling (low ne) ~ no retention High fueling (high ne) significantretention

Kubo et al., IAEA 2006


Strong retention in Alcator C-mod

- Pulse duration of ~ 2 sec, but very high plasma density.-16 repeated discharges (~ 30 s plasma exposure w/o disruptions)- Retained D fluence remains linear with incident D ion to the wall at an average rate of 0.75%

D Whyte et al., IAEA 2006 Metallic device (Mo, room temperature) Co-deposition ?


Recovery after/between pulses

RetentionShort pulse ~ 10-30%Long pulse/Strong injection ~ 50%

• Small fraction recovered after shot, but > plasma content (C, C-W and Be)

• Independent of inventory cumulated during the pulse (TS, JET, AUG)Except for disruptions, this amount is independent of Ip, BT, density, input power, fuelling method.

[V. Mertens et al., EPS 2003] AUG

30

25

20

15

10

5

0

Tot

al D

rec

over

ed a

fter

pul

se (

1021

)

5004003002001000

Total D injected during pulse (1021

)

JET, Twall=200°CMKII_SRP DivertorMKII_HD Divertor

JET

t

wall

• Recovery ~ retention in phase 1 Transient mechanism


D Whyte et al., IAEA 2006

Strong retention…and recovery in Alcator C-mod

Net depletion of D fuel from the wall is observed

Cummulative effect of planned disruption H/D recovery over a C-Mod run day.


Integrated balance - Day

--- Total Injected--- Total exhausted--- Outgased between pulses

6

5

4

3

2

1

0

Part

icle

s (1

023

)

00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00

Time (h)

Short pulses

Long discharges

TS

Short discharges•Recovery between pulses is significant•Cumulated inventory can be ~ recovered by conditionning (GDC…): Overall balance ~0

Long discharges•Same recovery between pulses but negligible compared to the overall balance

Significant inventory built up proportional to discharge duration (at least in limiter machine)

Phase 1

Phase 2


Steady state retention – Saturation ?

- “Wall saturation” is a “local” de-saturation of overheated PFCs.- BUT does not prevent and/or cancel retention in other areas (layers, gaps, below divertor…)- No wall saturation in the sense of “no retention” observed.

- Uncontrolled outgassing is no more observed in “fully” actively cooled devices (TS); the source is constant. - Retention rate is also constant and for the same plasma, no “history effect” is observed.

TS before “before upgrade”, “only”80% actively cooled and no pumping

0 20 40 60 80 100 1200

0.5

1

1.5

2

2.5

3

3.5

4

Time (s)

Cen

tral

Lin

e D

ensi

ty (

101

9 m

-2)

267764.5MW

192492.5-3MW

196211.8MW

196221.8MW

199802.4MW

199762.4MW

- Result of overheated PFCs and as Tsurf

increases outgassingEventually, Outgassing > Exhaust loss of density control (also observed on JET w/o pumping and JT-60U w div. pumping)

C Grisolia et al., PSI 1999

TS

T Nakano et al., IAEA 2004


Integrated gas balance – Day - Week

Integration over a campaign : long term retention Retention = Ninj – Nrecovery- Ndisruptions - Ncleaning

Gas balance accuracy limited by the requirement to substract pairs of large numbers.

For integrated balance of the order of week the accuracy strongly depends on - the “time” for the integration (pulse~10 sec, day~105 sec), - evaluation of the outgassing flux, D and CxHy released (disruptions)

Gas balance is an upper limit of the retention

Fuel retention over period ~ day/week complementary method required:Post-mortem analysis of samples from limiters, main chamber, deposition in gaps in between tiles, below the limiter/divertor…But this analysis cannot include all PFCs and air (H20) exposure during transfert.

Post mortem analysis is a lower limit of the retention

Recovery DisruptionCleaning …


0

1000

2000

3000

4000

5000

6000

64800 65000 65200 65400 65600 65800

JET pulse #

1

3

4 6

7

8

L B S R P#649

76#64980

QMB4

1

3

4 6

7

8

LBSRP

#652

81#6

5282

QMB4

1

3

4 6

7

8

LBSRP#654

07#654

09

QMB4

1

3

4 6

7

8

LBSRP

#656

67

#656

68

QMB4

ISP at horizontal tileintegral erosion

ISP at vertical tileintegral deposition

ISP at hori-zontal tileintegral erosion

ISP at hori-zontal tileintegral erosion

ISP at vertical tileintegral deposition

Quartz Micro Balance

Integral deposition when inner strike point at vertical tile 3Integral erosion when inner strike point at horizontal tile 4

QMB4 (LBSRP) integral behaviour for restart / commissioning phasefr

equ

ency

[H

z]

G Esser et al.,


D/C

0.12

0.090.05

0.320.310.280.13

1 0.05 0.3 0.38

Fuel retention in JET (MKII GB)

(NRA: D/C ratio, SIMS: layer thicknesses)Only plasma facing surfaces at divertor included (not tile gaps, inner limiters...)

MkIIGB

Divertor time: 57500 sec (16 hours)

D injection: 766g

Inner ion flux: 1.3x1027

C deposition: 400g

Rate: 3.4x1020Cs-1

Inner Divertor: D/C~0.2

J Likonen, P Coad et al.,

-D retention in the divertor: 3% (Mk-IIGB)


38 g

73 g

55g

63g

300g 5g

Total inner: 603 g Total outer 380g

Fuel retention in JET (MKII-SRP)

- D retention in the divertor: 2.4% (MKII-SRP), 3% (Mk-IIGB), consistent with DTE1 results ~2% (Mk IIA, 0.2 g in tiles 0.5 g in 150 g flakes).- Lower limit: analysis does not include all PFCs (SRP, main chamber…)- Flakes in subdivertor after DTE1 ~1 kg : “seen” but not quantified ~ 3g

MkII-SRP

D injection: 1800g

C dep: inner (outer): 603g (380g)

C dep rate: 3.7 1020s-1 (2.2 1020s-1 )

Inner (outer) divertor D/C~0.3 (0.2)

D retention inner: 1.6% (30g)

D retention outer: 0.8% (12.6g)

Total D retention 2.4% (42g), no

SRP, no main chamber

P Coad, A Windowson et al.,


W-coverage in ASDEX-Upgrade

2002/2003 2004/2005

• Increasing coverage with W

• Regular boronizations about 8 per discharge period Mainly effective in main chamber

6370 s75.4 g D

3864 s43.9 g D

B-concentration in main chamber deposits

2002 80%2005 74 – 98%

M Mayer


0

2

4

6

8

B + C D measured D assumed

9C456B6A

De

po

sitio

n [1

019 a

t./cm

2]

2002/2003 campaign: Mainly carbon machine (45% W) Retention governed by trapping on inner tile surface (70% inner divertor tiles, 20% in remote ares (below roof baffle,...) Total retention ~4% of input (10-20% from gas balance)

2004/2005 campaign: Full W machine except the divertor (Carbon)

No significant difference in retention between 2002/2003 and 2004/2005

AUG: 2002/2003: Deposition of D and C

M Mayer et al., PSI 2004


Hydrogen retention and carbon deposition in JT-60U

K Masaki et al., IAEA 2006

Highest (D+H) retention ~16x1022 m-2 on layer on outer dome wing and highest concentration (D+H)/C ~13%

In plasma-shadowed area underneath the dome, ~2m layers found (8x1019 Cs-1) and a very high concentration (D+H)/C ~80%


Retention mechanism

Adsorption : phase 1

AUG, JET, TEXTOR, TS

Implantation (saturates, sensitive to Tsurf) : TS, JET and JT60U

Bulk diffusion (long pulse / high flux, high Te) Suspected to play a dominant role in long pulse in TS

Codeposition (low Te, cold shadowed areas in direct line of sight of C source) : supposed to be the dominant process (AUG and JET)

Density control

Detritiation (depth in C)

Detritiation (remote areas)

ITER

Limited (released after shot)

Limited (reservoir >> plasma)

(fluence) 0.5 for CFC (Lab exp)(not for graphite)

(fluence)

Fuel retention mechanisms (in C)

Main open issue : Dominant retention mechanism with mixed materials (C/Be/W) ?

Courtesy E Tsitrone


M Sakamoto al., IAEA 2006

Real time measurement of Co deposition in TRIAM

- In situ and real time measurement of erosion/deposition based on interference of a thin semi-transparent layer.- Located 7.5cm from the LCFS and viewing a poloidal limiter

Growing rate ~2.3x10-4 nm s-1 (~1.5x1016 Mo m-2s-1)Retention ~ 4 1017 Hs-1 (8x1021H after 5h25 of plasma)Similar to Alcator-C (11x1021D in 30 sec) …lower flux but longer duration!

Constant increase of wall inventory and growth of deposited layer of Mo


In these samples the D is trapped in the 3.7 m deposited layer (~40%) - D located in depth (up to 10m) >> the ion implantation (few nm)

CFC samples (Sepcarb® N11) exposed in the SOL of TS

3.7 m

No saturation observed with fluence


Open porosity at the matrix/fibre interface significant role in D migration ?

Analysis of these CFC samples (Sepcarb® N11)

No modification of the C hybridization in both the CFC matrix and the fibers observed with Electron Energy Loss Spectroscopy (EELS). No C-D chemical bondingTransport mechanism and D migration in the bulk (8m) to be investigated


SummaryGas balance and fuel retention: Large data base with carbon showing common features for the retention (AUG, JET, TEXTOR, Tore Supra, but also JT-60U, LHD)- During pulse: significant retention unless low fuelling- Long term: ~0 for short pulse, significant for long discharges (TS)- No “wall saturation” (sense of no retention) is observed for actively cooled devices- Recovery after pulse independent of the cumulated inventory

Retention in carbon dominated devices:~10-20% (Gas balance: upper limit) ~ 3-4% (Post-mortem: lower limit)Still no influence of W (AUG: 80%) on the retention (ELMs ? AUG &JET)

Co-deposition dominant process (AUG and JET)

New results w/o C as PFC: Full W (AUG) and W-Be (JET) (Alcator-C, Triam) Co-deposition cancelled with full metallic machine and therefore should significantly reduce the retention compare to Mo ! Future exp in AUG (series of experiments on gas balance proposed), JET (2 gas balance experiments late 2006 and early 2007) and TS (Sector of TPL removed for analysis)

ITER: 200 Pam3s-1, D-T 50% (5 1022Ts-1 for 400sec), assuming retention similar to carbon devices ~70 (5%) before reaching 350g detritiation

1 th loarergas balance and fuel retention – eu tf on pwi – 13 november 2006 th loarer with...

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