1 Th LoarerGas balance and fuel retention – EU TF on PWI – 29 October 2007 Madrid Th Loarer with...

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


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


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


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%)


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


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


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


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%


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)


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





E Tsitrone et al


UFOs on CCD imaging of the TPL

E Tsitrone et al


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)


Inventory proportional to discharge duration

Disch. OK

Disruptions

Outgassing

Trapping

E Tsitrone et al


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


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


Phases of discharges observed in C

Typical discharge “puff and pump” steady phase reached after ~2sec

V Rohde et al.


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.


Gas balance with W wall

Wall loading observed, no steady state reachedV Rohde et al.


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.


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.


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


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


●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;


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


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.


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.


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


J Likonen et al

Deposition at OPL and IWGL (MkIISRP, 2001-2004)


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)


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


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


• 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


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


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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