1Th LoarerGas balance and fuel retention – IAEA Chengdu – 18 October 2006 TEC Euratom Th Loarer...

1Th Loarer Gas balance and fuel retention – IAEA Chengdu – 18 October 2006

TECEuratom

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 in Fusion Devices

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


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.

INTRODUCTION

Results from different tokamaks

Limiter machine Divertor machineTEXTOR Tore Supra

Full carbon Full Carbon Actively cooled

Long discharges

ASDEX Upgrade JET

First wall: W High performances Divertor: C Carbon, Berylium

- In the frame of the EU TF on PWI, efforts are underway to investigate the gas

balance and fuel retention during discharges and integrated over experimental

campaign. The aim is to assess the dominant processes of the fuel retention and to

extrapolate to ITER.


TECEuratom

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 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


TECEuratom

Recovery after/between pulses

• 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

wall

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

t

• Recovery ~ retention in phase 1 Transient mechanism


TECEuratom

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


TECEuratom

Steady state retention – Saturation ?

- “Wall saturation” is a “local” de-saturation of overheated PFCs.

- BUT does not prevent and/or cancel retention (layers, gaps, below divertor…)

- Wall saturation in the sense of “no retention” has not been observed yet.

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)

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

C Grisolia et al., PSI 1999

TS


TECEuratom

Integrated gas balance – Day - Week

Accuracy in gas balance studies likely limited by the requirement to substract pairs of large numbers, with inherent accuracy.

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

For integrated gas balance and fuel retention over periods longer than a day or a week, complementary methods are required:Post-mortem analysis of samples from divertor/limiters, main chamber, deposition in gaps in between tiles, below the limiter/divertor…

But this analysis cannot include all PFCs.

Post mortem analysis is a lower limit of the retention


TECEuratom

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

Retention of 3% (25g)

J Likonen, P Coad et al.,

- D retention in the divertor: 3% (Mk-IIGB), 2.4% (MKII-SRP).


TECEuratom

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


TECEuratom

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


TECEuratom

SummaryGas balance and fuel retention: Large data base with carbon showing common features for the retention (AUG, JET, TEXTOR, Tore Supra)- 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)

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

New results without C as PFC: Full W (AUG) and W-Be (JET) Co-deposition cancelled with full metallic machine and therefore should

significantly reduce the retention


TECEuratom


TECEuratom

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.,


TECEuratom

GAS BALANCEJETTEXTORTore SupraAUG (Integrated over the pulse duration)

Balance verified at any time during and between pulses

Particle InjectionGas, NBI, Pellets

Wall

tt

e

t

pellet

t

NBI

t

gas NdtDivertordtVesselNdtQdtQdtQ 00000

INJECTION PLASMAScenario

EXHAUST(Vessel and Divertor)

WALL (Retention),Scenario, PFCs,…

“WALL”

PLASMA

“Mid-plane”

Particle ExhaustDivertor


TECEuratom

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%


TECEuratom

0 200 400 600 800 1000 1200 14000

1

2

3

4

0

200

400

600

D D 1000 keV D assumed

321up

1low9A9B9C456B6A

Am

ou

nt o

f D [1

019 a

t./cm

2 ]

s-coordinate [mm]

Str

ike

po

int [

s]

Comparison of 2002/2003 and 2004/2005

0 200 400 600 800 1000 1200 1400 16000

1

2

3

4

0

100

200

300

400

500

2500 keV 800 keV

Am

ou

nt

of

D [

10

19 a

t./c

m2 ]

s-Coordinate [mm]

3up

321up

1low

456B6A

Dis

ch

arg

e t

ime

[s

]

9

2002/2003 2004/2005

No significant change in D retentiondespite replacement of C by W in main chamber


TECEuratom

1019 1020 1021 1022 1023 1024 1025 10261019

1020

1021

1022

1023

1024

1000 eV

0.5

CFC, PISCES-A Emmoth, NF 30 (1990) 1140

0.15

0.26

100%

rete

ntio

n

Pyrolytic graphite

Fine grain graphitegraphitised

at 1000°C at 2100 to 2750°C

Ret

ain

ed D

(D

/m2 )

Fluence (D/m2)

150 eV

Status of knowledge on D retention

in carbon materials

Retention of implanted D in graphite saturates at about 1021 D/m2 depending on energy→G. Staudenmaier, J. Roth et al., JNM 84 (1979) 149

No complete saturation for fine grain graphites and CFC, depending on porosity→A.A. Haasz et al., JNM 209 (1994) 155→B. Emmoth et al., Nucl. Fusion 30 (1990),1140→M. Balden et al., Phys. Scripta T103 (2003) 38


TECEuratom

DTE1 experiments in JET


TECEuratom

Poloidal distribution of T in JET

JET T (DTE1) : 6.1 g left (17%) before ”Venting”2.4 g removed with H2O from air

3.7 g left (10%)

[N. Bekris et al., JNM 2005]

3 g remaining in subdivertor flakes (~1 kg : seen but not quantified)

0.2 g in tiles0.5 g in 150 g flakes(D/C~1 in cold deposits)0.7 g found (2 %)


TECEuratom

Sputtering of C by D :

Temperature (K)

Sp

utt

eri

ng

yie

ld (

ato

ms

/io

n)

1 keV D on C

Implications of Tsurf cte

To be kept in mind when interpreteting experiments with evolving Tsurf

[Nuc. Fus special issue 1, 1991]

(°C)Temperature (°C)

Saturated concentration of D in C :

Fuel retention : implantation / desorptionNet wall pumping outgassing

Fuel retention : codeposition

Tsurf : key parameter for “chemistry” of carbon

Chemical erosion

Phys.Sputt

RES

Thermalsublimation

200 450 700 950 1200 1450 1700

T(°C)

1Th LoarerGas balance and fuel retention – IAEA Chengdu – 18 October 2006 TEC Euratom Th Loarer...

Documents

Transcript of 1Th LoarerGas balance and fuel retention – IAEA Chengdu – 18 October 2006 TEC Euratom Th Loarer...