Member of the Helmholtz Association Fuel retention in carbon materials Arkadi Kreter et al

Mem

ber

of

the H

elm

holt

z A

ssoci

ati

on

Fuel retention in carbon materials

Arkadi Kreter et al

Arkadi Kreter et al. "Fuel retention in carbon materials" EU-TF PWI SEWG on fuel retention/removal, Cadarache 15 June 2009 3

Extensive database on retention in CFC/FGG

Analysed materials:

CFC NB41 (new EU ITER grade) [1]

CFC NB31 (former ITER grade) [2]

CFC DMS780 (JET) [2]

CFC DMS701 (ASDEX Upgrade) [3]

CFC N11 (Tore Supra) [4]

fine-grain graphite (FGG) EK98 (i.e. TEXTOR) [2]

FGG IG-430U (ALT-II TEXTOR)

FGG ATJ (DIII-D) [1]

Exposures in:

PISCES-A/B [1,3,4], TEXTOR test limiter [2], TEXTOR ALT-II main limiter

[1] A. Kreter et al., PFMC-12, Jülich 2009[2] A. Kreter et al., J. Phys.: Conf. Series 100 (2008) 062024[3] R. Pugno et al., J. Nucl. Mater. 375 (2008) 168[4] J. Roth et al., J. Nucl. Mater. 363–365 (2007) 822


Exposures in PISCES-A/-B linear plasma devices

ErodedMaterial

PISCES (-A, -B) schematic view

Steady-state plasma

ne = (2-3)·1018 m-3 ; Te = 7-15 eV

= (3-6)·1022 D/m2s

Variations of:

Ei = 20 - 120 eV

= 1·1025 - 5·1026 D/m2 (~1 ITER pulse at strike point)

Ts = 370 K ('cold' ITER wall) - 820 K (ITER strike point)

Controlled Be, He and Ar seeding

All experiments in erosion-dominated conditions

PISCES-A plasma and target

Ex-situ analysis of samples for retention

• Thermal desorption spectrometry (TDS)• Nuclear reaction analysis (NRA) with 3He

beam

B


Exposures on test limiter in TEXTOR tokamak

Test limiter with CFC/FGG stripes

59mm

30 o

60m mtoroidal d irectionpoloidal direction

r=a=460m m

r=461.5m m

r=490m m

r

NB

31

DM

S780

EK98

32 reproducible Ohmic discharges in 80% D

177 s total duration

Limiter tip at LCFS (0.46 m)

neLCFS 1·1019 m-3 ; Te

LCFS 45 eV; Ti Te

LCFS 2.9·1025 D/m2; SOL() 12 mm

Tlim 500 K

Ex-situ analysis of samples for retention

• Thermal desorption spectrometry (TDS)• Nuclear reaction analysis (NRA) with 3He

beam• High-resolution NRA with m-size 3He

beam (-NRA)


Retention in NB41: Fluence dependence

M=4 (D2) desorption spectra(Ts = 470 K, Ei = 120 eV)

400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

D2 d

es

orp

tio

n f

lux

[x

10

19 D

/m2 s

]

Temperature [K]

=50e25 D/m2

10e25

3e25

1e25

470

K

Ret

enti

on

[D

/m2 ]

Ion fluence [D/m2]

NB41 PISCES-A [1] N11 PISCES-A [2] NB31 TEXTOR [3] DMS780 TEXTOR [3] EK98 TEXTOR [3]

1024 1025 1026 1027

1021

1022

0.35

Total D retention for exposures at Ts = 470 K, Ei = 120 eV

No saturation up to =51026 D/m2

ATJ PISCES-A [1]

[2] A. Kreter et al., J. Phys.: Conf. Series 100 (2008) 062024[1] J. Roth et al., J. Nucl. Mater. 363–365 (2007) 822

Similar behaviour for different CFCs and fine-grain graphites

0.5 K/s

[1] A. Kreter et al., PFMC-12, Jülich 2009


400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

D2

des

orp

tio

n f

lux

[x10

19 D

/m2 s

]

Temperature [K]

Ts=470 KTs=370 K

Ts=820 K

470

K

370

K

820

K

Higher retention for lower exposure temperatures due to additional trapping sites

and higher population

M=4 (D2) desorption spectra (Ei = 120 eV, = 2.4e26 D/m2)

Ret

enti

on

[D

/m2 ]

Ion fluence [D/m2]1025 1026 1027

1021

1022

Total D retention for exposures at different temperatures in PISCES-A and -B

Higher retention for lower Ts

Saturation for Ts > ~800 K

[1] R. Pugno et al., JNM 375 (2008) 168

Saturation

NB41 Ts=370K NB41 Ts=470K NB41 Ts=820K DMS701 Ts=1070K [1]

Retention in NB41: dependence on exposure temperature

0.5 K/s


Retention in NB41: dependence on ion energy

Higher retention for higher incident ion energy

400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

1.0

Temperature [K]

D2 d

es

orp

tio

n f

lux

[x

10

19 D

/m2 s

]

Total D retention vs Ei

( = 1e26 D/m2, Ts = 470 K)

0 20 40 60 80 100 120 1400

1x1021

2x1021

3x1021

4x1021

5x1021

6x1021

7x1021

Re

ten

tio

n [

D/m

2 ]

Incident ion energy [eV]

M=4 (D2) desorption spectra ( = 1e26 D/m2, Ts = 470 K)

Ei=20eV

Ei=50eV

Ei=120eV

0.5 K/s


Retention in C: dependence on ion flux

Data from PISCES and TEXTOR exposures compared to data from ion-beam facilities

[J. Roth et al., JNM 363–365 (2007) 822]

Ion beam data show higher retention than data from plasma devices Can be attributed to flux dependence (higher retention for lower fluxes)

Typical ion fluxes

Ion beam: 41019 m-2s-1

PISCES, TEXTOR: ~1022 - 1023 m-2s-1


ALT-II main limiter in TEXTOR tokamak

Inside view of TEXTOR

History of analysed tile:

Exposed 2004 - 2008

Pulses: 8534; Plasma: 43473 s

Area-averaged H+D fluence: 1.4e26 m-2

Temperature 400 K – 650 K

Analysis for retention by laser desorption

Laser desorption parameters:

t = 1.5 ms

A= 0.05 cm2

P= 70 kW/cm2

main toroidal limiter ALT-IIa = 0.46 m


ALT-II main limiter in TEXTOR tokamak

D retention in erosion zone: ~5e21 D/m2, or ~1e22 D for total ALT-II

D retention in deposition zone: ~1e23 D/m2, or ~1e23 D for total ALT-II

Retention in TEXTOR is dominated by co-deposition (~90%)

Analysis for retention by laser desorptionR

eten

tio

n [

m-2]

Poloidal position along tile surface [mm]

deuteriumhydrogen

depositionzone

erosionzone

depositionclose to bolts


Long-term exposure vs dedicated experiments

Ret

enti

on

[m

-2]

Ion fluence [m-2]

NB41 PISCES-A N11 PISCES-A NB31 TEXTOR DMS780 TEXTOR EK98 TEXTOR

1024 1025 1026 1027

1021

1022

0.35

ATJ PISCES-A

Retention in long-term exposure in good agreement with dedicated experiments

Retention in bulk of CFCs and FGGs

H+D ALT-II TEXTOR(comparable Ts, Ei, )


0 1 2 3 4 510-4

10-3

10-2

10-1

100

D a

tom

ic c

on

ce

ntr

ati

on

Depth [m]

Retention in NB41: D penetrates deep in bulk

NRA depth profile of NB41 (=31025 D/m2, Ts=470 K, Ei=120 eV)

18 at% of D at surface saturated implantation layerPenetration in bulk

-NRA 2D mapping of D in NB31 exposed in TEXTOR

for = 1.21025 D/m2 at Ts = 500 K

exposedsurface

cleavage

-NRAmapping

20

10

30

00 20 40 60 80 100

D a

mou

nt [c

ount

s]

Depth [ m]

2001000 300 400 500Distance along surface [ m]

020406080

100120

Dep

th [

m]

01234567

D amount [counts]

Inhomogeneous penetration of D in bulk over tens of m

A. Kreter et al., J. Phys.: Conf. Series 100 (2008) 062024

P. Petersson et al., PFMC-12, Juelich 2009

2 MeV 3He+ beam


Influence of Be on retention

D2 TDS spectra for ATJ exposed w/o and with Be (Ts=720K, Ei=35 eV)

Be carbide layer appears to prevent increase of retention with fluence

Total Deuterium Retention

With Be, =0.5e26 D/m2 before Be, =2e26 D/m2 total:

1.9e21 D/m2

Pure D, =2e26 D/m2:

2.3e21 D/m2

Pure D, =0.5e26 D/m2:

1.6e21 D/m2400 600 800 1000 12000.0

0.1

0.2

0.3

0.4

0.5

pure D =0.5e26m-2

pure D=2e26m-2

Be containingplasma

D2 d

eso

rpti

on

flu

x [x

1019

D/m

2s]

Temperature [K]

Scenario of Be experiment

1. Establishing background plasma (=0.5e26 D/m2)

2. Be injection from oven (total =2e26 D/m2)

0.5 K/s


400 600 800 1000 12000.0

0.1

0.2

0.3

0.4

0.5 D D+Be D+Be+He

D2 d

es

orp

tio

n f

lux

[x

10

19 D

/m2 s

]

Temperature [K]

Influence of Be+He on retention

D2 TDS spectra for ATJ exposed to pure D, D+Be, D+Be+He (Ts=720K, Ei=35 eV, fHe=16%)

He appears to change the retention mechanism and reduce retention

Sensitive to exposure parameters (not effective at high Ei)

Similar effect of Argon

Total Deuterium Retention

D+Be, =0.5e26 D/m2 before Be, =2e26 D/m2 total:

1.8e21 D/m2

Pure D, =0.5e26 D/m2:

1.6e21 D/m2

D+Be+He, =0.4e26 D/m2 before Be, =1.7e26 D/m2 total:

0.5e21 D/m2

0.5 K/s


Summary and discussion: pure D plasma (I)

In-bulk retention is similar in different CFCs and fine-grain graphites CFCs and fine-grain graphites are porous

In-bulk retention is higher for lower exposure temperatures Additional trapping sites at lower temperatures Higher population of available trapping sites at lower temperatures

In-bulk retention scales as fluence with depending on temperature:

<~0.5 for low Ts (surface diffusion along pores)

=0 for Ts>~800K – saturation of retention for < 31025 D/m2 (few sec of ITER pulse)

1. Incident deuterium ions saturate the implantation layer (~10-100 nm)2. The level of saturation is defined by the balance between adsorption and ion-induced

desorption for a given number of available trapping sites3. From the implantation layer, D 'diffuses' further in-bulk along surfaces of the pores


Summary and discussion: pure D plasma (II)



In-bulk retention is higher for higher incident ion energies Higher D concentration in implantation layer [Staudenmaier JNM79] leads to higher D

amount in bulk

In-bulk retention is higher for lower fluxes Amount of diffused deuterium t, longer time available for D to diffuse in for the same

fluence


Summary and discussion: influence of impurities



With addition of Be no further increase of in-bulk retention Be carbide layer appears to suppress the in-bulk penetration of deuterium (Be2C layer

thickness is a few 100 nm)

He and Ar impurities decrease the in-bulk retention Presumably due to depletion (ion-induced detrapping) of the implantation layer, from

where it otherwise moves deeper in the bulk• Do impurities deplete co-deposited layers from D? To be tested experimentally

Documents

Member of the Helmholtz Association Fuel retention in carbon materials Arkadi Kreter et al