1 th loarerfuel retention in tokamaks – psi conference 26-30 may - toledo euratom th loarer with...

1Th Loarer Fuel retention in tokamaks – PSI Conference 26-30 May - Toledo

Euratom

Th Loarer

with special thanks to

N Bekris, S Brezinsek, C Brosset, J Bucalossi, P Coad, G Esser, W Fundamenski, E Gauthier, A Kreter, J Likonen, B Lipschultz, M Mayer,

P Monier-Garbet, Ph Morgan, R Neu, B Pégourié, V Philipps, R Pitts, V Rohde, J Roth, M Rubel, C Skinner, J Strachan, E Tsitrone.

And alsoEU TF on PWI and JET EFDA contributors

Fuel retention in tokamaks


Euratom

OUTLINE

- Introduction

- Evaluation of fuel retention in tokamaks

- Gas Balance

- Post mortem analysis

- Extrapolation to ITER

- Summary


Euratom Introduction

- Evaluation of hydrogenic retention in present tokamaks is of high priority to

establish a database and a reference for ITER (400 s…usually 10-20 s 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 T-

limit (350/700g) in ~35/70 pulses.

- Retention rates of this order or higher (~20%) are regularly found using gas

balance.

- Retention rate often lower (3-4%) are obtained using post mortem analysis


Euratom

D,T

Wall

Mechanisms for fuel retention

Two basic mechanisms for

Long term fuel retention

Deep Implantation, Diffusion/Migration, Trapping

C, Be C, Be, D ,T

Codeposition

Short term retention (Adsorption: dynamic retention)

~ Recovered by outgassing

In tokamaks today Two complementary methods

Gas balance How much ? During the pulse / integrated pulse/days.

Post mortem Where and how? Integrated over experimental campaign


Euratom Gas balance

Divertor cryo-pumps

PlasmaCalibrated Particle Source

(Gas, NBI, pellets)

Exhaust by NBI boxes, Diag…

Retention

Short & Long Term

1 - Function of time - Measurement of the Injected and pumped fluxes (Pressure gauges and pumping speed) 2 - Integral of Pumped flux + intershot outgassing (~ Short Term Ret ) (Collected in a calibrated volume).

Separate Short and long term retention

Gas Balance Retention = Injection - Pumped + Plasma


Euratom Retention: Short and long term

Short term retention- Depends on plasma scenario, wall conditioning and Material (Be, C)…-“Limited” to “fast” reservoir and recovered in between pulses (outgassing)

Actively cooled device Steady state operation-->Long term retention

Long term retention

- Co-deposition Correlated to C production

- Implantation Edge plasma, material structure…

Long term retention

Short term retention

5

4

3

2

1

0

1020

Ds-1

4003002001000

Time (s)

# 32299 # 32300

TS

Dynamic retention: ≈ 5 x1021D JET ≈ 2.5 1022 D ~ wall area ratio


Euratom Plasma scenario: C prodution

- Long term retention- Drop by ~60% when moving from L-mode to Type III H-mode.- Increases by ~60% when moving from L-mode to Type I H-mode.

Retention correlated to increase of C erosion

T Loarer et al., EPS 2007

Pulse type Divertor phase (s)

Injection(Ds-1)

Long term retention (Ds-1)

L-mode

2 MW

126 ~1.81022 1.341021

Type III

6 MW - <5-10 kJ

350 ~0.61022 0.81021

Type I

13 MW – 100 kJ

50 ~1.71022 2.081021

Series of repetitive and consecutive discharges (~no history effect)


Euratom Carbon production and scenario

- DTE on JET and TFTR (at high NBI power more T retention by co-deposition)

C Skinner et al. JNM 1997, 1999

J Strachan et al. Nuc. Fus. 2003

L mode(3-4MW)

Type IH mode

10-15MW

- Increase of carbon source depends on scenario (ELMs, recycling flux…) enhanced retention by co-deposition

- Increase by a factor of ~2 of carbon source from L to type I ELMy H-Mode


Euratom Implantation and “wall” saturation

- As Tsurf increases Strong outgassing of D, CxDy from target plates (eventually lost of ne control)

- Outgassing signature that implantation is saturated for overheated PFCs

- Also observed on long discharges in TRIAM-1M, Tore Supra. (Sakamoto et al. IAEA 2006, JNM 2007 Grisolia, JNM 1999, ).

Nakano et al. IAEA 2004, Nuc Fus 2006

But, with gas balance analysis this strong outgassing “hides” co-deposition.

And since carbon source increases this enhances retention by co-deposition.


Euratom Inventory proportional to duration

30x1021

20

10

0

-10

Wal

l inv

ento

ry (

D)

140120100806040200

Discharge duration (s)

Trapping

Outgassing

Normal discharges Disruption

B Pégourié I-21

- Recent exp. campaign of 10 days on TS repeating the same long pulse (2min – 2MW)

- Total of 5 h of plasma w/o conditioning

Sugiyama et al. Pys. Scrip 2004,Skinner et al, EPS 2001

- Steady state retention and wall inventory proportional to plasma duration - Weak recovery by outgassing and also by disruptions, independently of the

amount retained. DDC in TFTR after DTE (Skinner JNM 1997, 1999) and JET V Philipps P1-63


Euratom Retention in carbon devices

Retention by co-deposition dominates

Limit/cancel co-deposition ? High Z

Skinner et al. JNM 1997, 1999 T Nakano et al. JNM 2007

V Mertens et al. EPS 2003 Lasser et al. FED 1999

Long term retention

Cumulative, proportional to pulse

duration and linked to Carbon source

(recycling, ELMs…) JET, JT-60U, AUG, TEXTOR, TS… DT exp on JET and TFTR

Continuous increase of T inventory as the T operations are going on and dominated by co-deposition

TFTRP Andrew et al. FED 1999


Euratom High Z – Alcator C-Mod

D Whyte et al., IAEA 2006

~4x1021D

D Whyte et al. IAEA 2006,B Lipschultz et al., PSI 2008

- 16 repeated pulses (w/o disrp) in cleaned Mo walls - Retained D fluence remains linear with incident D ion

~3.5x1020Ds-1

- Net D wall recovery with planned disruptions

B Lipschultz I-14

- Mo retention proportional pulse duration Implantation? Co-deposition with B?

- Effective D recovery by disruption with Mo as PFCG Wright I-19


Euratom High Z - W in ASDEX Upgrade AUG from “all C” to “all W” (Carbon free)

- With 70% of W the retention was still around 10-20% (C dominated)- 100% W significant drop of retention below 1%

~45% W~70% W

V Mertens et al., EPS 2003, V Rohde et al. EPS 2007

dom. ICRH 2004

100% Ww/o Boronisation

V Rohde P1-61R Dux I-06


Euratom

Where is the fuel retained?

Post mortem analysis


Euratom

Method Principle Quantity measured

SIMSSecondary Ion Mass Spectroscopy

Incident ion flux (Cs+, Ar+, O+) with an angle ~20-30° with respect to the surface

-Analysis of “sputtered” ions +CH3, +CH4… and/or ionised fragments-Depth ~m

RBSRutherford Back Scattering

He+ incident beam (protons) @~1-3MeV)Measurement of the energy of the reflected beam

Analysis of the elemental surface.From nm to mm

TDS

Thermodesorption

Temperature ramp up (room up to 1600K) of a sample.

Under vacuum or inert atmosphere (Mostly Ar or He) w or w/o H2

Total quantity of H, D, O, CxDy …trapped in the material, coupled to Mass Spectrometer

Activation Energy

NRANuclear Reaction Analysis

Nuclear reaction triggered above an energy threshold of the incident 3He beam~1-3MeV 2D(3He,p) 4HeTarget 2D, particle analysed: p, “product” 4He 10Be(3He,p) 12B -- 12C(3He,p) 14N -- 13C(3He,p) 15N

Ratio D/C, Be/CDepth profile1Mev~1.5m2.5MeV ~7.5m

PIGEProton Induced Gamma Emission

13C(p,) N14 Use the narrow resonance for protons at 1.748MeV giving a 9.17MeV gamma ()

Concentration of 13C vs depth Smaller depth resolution, but detection limit ~10 times better than NRA)

NMRNuclear Magnetic Resonance

Resonance frequency proportional to the distance C—H of the element “connected” to H(D)

Used for liquids, in organic chemistry

Post Mortem Analysis

Wide range of methods for different objectives Surface analysis, Structure, Depth profile, Composition…


Euratom Where and how ? Implantation in CFCD retained in the samples (by TDS)

EK98DMS780NB31

Comparison with PISCES-A data

No saturation observed for these fluences and 0.5

Test limiter with material stripes exposed in TEXTOR

TEXTOR:

NB

31

ITER

DM

S780

JET

EK

98

Ts = 500K

A.Kreter et al. 2007

J Roth et al. PSI 2006.

Test limiter for dedicated experiments since removed at the end of the experiment; also the case of marker exp (13C)


Euratom Where and how ?: co-deposition with C

Dedicated 13C experiment to localize deposition and associated retention

Different Carbon erosion-transport and eventually co-deposition with plasma scenario L and H mode

Also 13C experiments inTEXTOR: P WIenhold et al. JNM 2001, JET: J Likonen et al. FED 2003, AUG: M Mayer et al. JNM 2005,JET: P Coad et al. Nuc. Fus. 2006.

DIII-D: Wamplers et al., JNM 2005, 2007

H-mode NRAL-mode NRAL-mode PIGE

3He,p NRA


Euratom

C-erosion/deposition: JET 2001-2004

Carbon deposition on PFCs

Louvre: 60g (from QMB)

17g

44g

67g

Negligible 19g

24g

Erosion

No clear erosion or deposition

105g 233g

99g

464g

From deposit thickness ( = 1.0 gcm-3 - 1.8 for the

substrate)

-Total C deposition

Inner: 625 g Outer: 507 g

J Likonen P1-70


Euratom

D/C ratios: JET 2001-2004

0.91 0.25

0.15

0.11

0.42

0.02

0.120.08

0.14

0.17 0.79

D/C ratio and retention

Injected : 1800g (5.381x1026D)

In the divertor area

Total D: 66 g = 3.7 % of inj

(2.2x1020Ds-1)

Retention 70% Inner + 30% Outer

J Likonen P1-70


Euratom 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 retention19μm

0.96 cm3

D/C=0.09

10μm

0.5 cm3

D/C=0.02

0.9μm

0.04cm3

D/C=0.13

3μm

0.2cm3

D/C=0.13J Likonen P1-70

M Mayer et al., PSI 2000, C Brosset et al, PSI 2004, 2006

JET:First wall~200°C

Divertor structure ~50°C

TEXTOR ~8-10% (300°C)Tore Supra ~10-15% (120°C)

~3.8%

- Gap inventory always

connected with C co-deposition

(large in gaps, small in narrow

castellated grooves)

M Rubel et al, JNM 2007


Euratom Temperature effect - JT-60U

Masaki IAEA 2006, Hayashi PSI 2006, Sugiyama PSI 2006, Hirohata PSI 2006

Twall= 300°C

6 years – 8h20 of NBI

- Higher Twall lower D/C ratio on PFCs

- No drop of co-deposition in remote area

Twall=150°C

3 years – 2h10 of NBI Long discharges

JT-60U “Normalised” to NBI time (8h20)

- Carbon: inner + dome ~550 g 1.0x1021/sec (2.7 times higher than in JET: 3.7x1020s-1 )

- Carbon: outer erosion ~340 g

210 g comes from the main chamber

PFC D/C~ 0.01-0.15

Remote D/C~ 0.75Same as JET 50°C

Retention ~ 1.3x1020Ds-1

(~8%)


Euratom

2002 – 20034940 s

6A

4

AUG – From all C to all W D inventory

W

C

C

C

C-dominated campaign 2002/2003

Normalised to 3000 s - D on divertor tiles 0.9 – 1.3 g- D below roof baffle 0.4 g

1.3-1.7g

Total D-inventory dominated by inner

divertor and remote areas

Long term inventory ~ 3–4%

M Mayer et al, Nuc Fus 2007


Euratom

20072620 s

6A

4

AUG – all W: Analysed tile D inventory

From C-dominated to all W D inventory reduced ~5-10 Retention<1%

W

W

W

W

M Mayer I-13

Full W camp 2007 – No Boronisation

Norm. to in 3000 s - D on divertor tiles 0.15 – 0.23 g- D below roof baffle 0.03 g

0.18-0.26g (drop ~7-10)

D retention in inner divertor still dominated by C-codeposition: drop ~10-15

D retention in outer divertor dominated by trapping in W – Drop ~5-10


Euratom Gas balance – Post mortem

Extrapolation to ITER

Post mortem analysis

- Accuracy of NRA, SIMS… ~ 10%- But cannot include all the PFCs, and effect of oxygen when removed from the vessel…

When analysing the “same plasma” Gas Balance and Post mortem lead to similar evaluation

- Accuracy ~10% for D (H) (Better: He or T)- But CxDy cont., long term outgassing...

Gas Balance

“Global measurement” for “specific” plasma conf. with “minimum” of power/gas

Pin~15-20MW – inj~2-3x1022Ds-1

“Local measurement” integrated over an exp. camp. Reflects the averaged discharge

Pin ~4MW, inj ~4x1021Ds-1

Long term Ret (10-20%) 4-8x1020Ds-1

Retention in the divertor area (MKII-SRP) + Subdivertor (as in JT 60U)Long term Ret 4x1020Ds-1


Euratom

All C reaches tritium limit (700g) in less than 30-40 discharges

All-W reduces tritium problem, but n-effects need to be considered

Fuel inventory estimates for ITER

- More R&D required for evaluation of n-effects:

- Need to improve modeling in retention by co-deposition/trapping (fluence…)

Evaluations based on ion + CX fluxes to the wall and resulting- Implantation- PFC erosion and associated co-deposition

J Roth R-1

Roth PPCF 2008


Euratom Summary

Gas balance:

Long term retention for C machine depends on Plasma scenarioAs far as C source exists co-deposition dominates, increases with C production recycling, ELMs (AUG, JET, JT-60U, TFTR, TS) and to pulse duration. Retention by implantation saturates for overheated PFCs (JT-60U) Long term recovery (outgassing and disruption) is weak (TFTR, JET and TS) Mo exhibits retention to plasma duration, but D recovery from disruption. Full W shows a significant drop of the retention ~1%.

Extrapolation to ITER

- A full C machine would reach the limit in “few” discharges of 400s

- A high Z device would limit the co-deposition and strongly reduce retention

Post Mortem analysis Confirms long term retention in PFCs is low but high in remote areas In carbon AUG-JET (3-4%), JT-60U~8%, TEXTOR & TS ~10-15% Significant drop of the retention below 1% in AUG with full W configuration

Complementary and reliable methods retention in full metal wall (ILW)


Euratom

END…


Euratom Short term: plasma scenario

ne~0.7nGW

PTOT (MW)NBI+ICRH~13MW

D(in) D (out)

Time (s)

#69260

Ip = 2.0 MA, B = 2.4 T

- 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.

WELM ~100 kJ ~ 60 Hz

T. Loarer et al., EPS 2007

Heating phase

Injection

Exhausted

Retention


Euratom Retention in gaps

2 decay lengths in TFTR1~2mm hydrogen rich deposition ((D+T)/C~0.2

prompt redeposition of C2Dx (1,3,5) ... with high

sticking coefficient 2~6-12mm influenced by the gap width (up to

30mm with large gaps) migration of neutral hydrocarbon with low sticking coefficient

T Tanabe et al. Fus Sci and Tech 2005

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

JET Be Limiter Tiles

- D deposition in the castellation 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.

TFTR


Euratom Retention in gaps

M Rubel et al, JNM 2007

Be limiter tiles of Mk-I divertor

Distribution of D on side surface in the gaps between the Mk-I CFC tiles.


Euratom Gas Balance: Accuracy

DT experiments in JET…over the first week the most difficult part to evaluate is the outgassing. In actual tokamak discharges.

Loarer JNM 2005

2.5x1024

2.0

1.5

1.0

0.5

0.0

e-

41800417604172041680Pulse number

Cumul T injected T retained at the end of the pulse PTE1 : Model Regenerated by cryopump Cumul T Outgased Net T Retained

Total of 11.743 g

50-50 % D-T

100% T 100% D

Max of 7.811 g

Max of 5.115 g

65% of retention during the pulses (~10sec)

40% of retention over the campaign

17% after intensive cleaning (~6 months)

T particle balances from Gas balance analysis Good agreement between gas balance and cryopump reg. (green points)


Euratom JET DTE Campaign

JET DTE Campaign

1997-1998T Vessel inventory

End of DTE1 campaign

Injected-Exhausted

(35g – 23.5g)

11.5 g

Clean up phase (D, H, He, Disrp, GDC…)

Remove 5.3g

6.2 g

Venting

Remove 2.5g

3.7 g

Flakes

Remove 0.5g

3.2 g

Inner and Outer wall

Remove 0.1g

3.1 g

480 Tiles of Divertor

Remove 0.1g

3.0 g still remaining (flakes)

After the campaign and intense cleaning campaign (pulses, conditioning, venting, the T inventory in the PFCs is “negligible”

(~0.2 g). Trapped tritium in flakes. Bekris et al. JNM 2005


Euratom JETand TFTR DTE Campaign

Skinner et al. EPS 2001

4.2g2.06g

Drop by a factor of ~2 in 11/2 year


Euratom High Z material: Alcator C-Mod

Wampler, IEEE 1999, PSI 1998

- OSP (net erosion): low D retention consistent with results from Mo erosion and B deposition.

-ISP Boron coverage is very small whilst D content is also very small

- Boron surface layers from boronisation was found at all locations except near the OSP

Dominant impurity: Boron and “some” amount of Mo


Euratom Gas balance: AUG - All W

V Rohde et al. this conf. P1-61

Gas balance divided in 3 phases- Limiter- Ramp up- Steady State Long term

Carbon PFC

W Main Chber

All W


Euratom DTE: TFTR and JET

C Skinner et al. 2002

Effect of oxygen on samples removed from device


Euratom DTE: TFTR



Euratom Location of TFTR tritium inventory



Euratom Co-deposition and Carbon production

- Increase of carbon source (ELMs, recycling flux…)

enhanced retention by co-deposition

Non-linear carbon deposition on ELM energy

Thermal decomposition of surface layers

1

3

4

QM

BA Kreter, G Esser et al sub PRL

A Kreter I-03


Euratom High Z exp in Alcator C-Mod

B Liptschultz I-14

- Although cleaning process allows to remove the boron layers, there is still a non negligible amount of boron at the surface

- If experiments are carried out in AUG with full W and boronisation, this could clarify the possible effect of boron in the retention behaviour observed in Alcator C-Mod


Euratom

One possible explanation are plasma impurities, largely B (~1 %), that are present in the C-Mod plasma and in the first 500 nm Mo tiles.

Overall, in both high-Z devices the campaign integrated retention on D is small, much smaller than for carbon or boron co-deposition.

Alcator C-Mod and ASDEX Upgrade

Alcator C-mod, Mo ASDEX Upgrade, W

Gas balance Variation between net outgassing and up to 50% retention, linear with number of discharges

~1% retention,

Post-mortem

≤ 1 % < 0.2 % retention(to be confirmed)

Modelling 1-2 % retention, linear with number of discharges

Roth R-1

1 th loarerfuel retention in tokamaks – psi conference 26-30 may - toledo euratom th loarer with...

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