9th international Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Salamanca, 2-3 June 2008 © Gasparyan Yury

The comparison of permeation and TDS The comparison of permeation and TDS experiments with polycrystalline tungstenexperiments with polycrystalline tungsten

Yu. Gasparyana,b, A. Rusinova, S. Stepanova, S. Yarkoa, N. Trifonova, A. Pisareva, A. Golubevac, A. Spitzync, S.Lindigb,M. Mayerb, J. Rothb

a Moscow Engineering and Physics Institute, Moscow, Russiab Max-Planck-Institut für Plasmaphysik, EURATOM Association, Garching, Germanyc RRC „Kurchatov Institute“, Moscow, Russia

9th international Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Salamanca, 2-3 June 2008 © Gasparyan Yury

Motivation

• W will be used in the divertor region of ITER and operate at elevated temperatures.

• It is important to know the hydrogen behavior in W at elevated temperatures for fuel balance and reactor safety (tritium inventory).

• The modeling of our IDP experiments gave defects with a detrapping energy of (2.05 ± 0.15) eV

• The existence of such defects should increase hydrogen retention in W at high temperatures.

Verify the existence of high energy defects using TDSVerify the existence of high energy defects using TDS

9th international Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Salamanca, 2-3 June 2008 © Gasparyan Yury

Sample

Polished unannealed W

Tungsten, cut from 50 μm thick foil with purity of 99.97 % (Plansee)

• Grain size of virgin sample: ~ 1μm• Before IDP samples are annealed at 900 K for 10 hours• Increasing of grain size after annealing?

After experiment at 600 C for several days, Ar cleaned side

9th international Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Salamanca, 2-3 June 2008 © Gasparyan Yury

Ion-driven permeation results

• Observed “effective diffusivity” were 4 orders of magnitude less than Frauenfelder’s diffusivity• Activation energy is ~ 2.05 eV too much for diffusion barrier• It is supposed due to trapping at defects

Temperature: 873-973 K

Ion energy: 200 eV/D

Incident flux: 1017-1018 D/m2sec

D2 pressure: ~ 7×10-4 Pa

0

20

40

60

80

100

1 кв 2 кв 3 кв 4 кв

ВостокЗападСевер

1.10 1.15 1.20 1.251E-14

1E-13

1E-12

1E-8

Effe

ctiv

e di

ffusi

vity

, m2/s

ec

1000/T, 1/K

ex1 (2.02eV) ex2 (2.16 eV) ex4 (2.16 eV) ex10 (2.14 eV) ex12 (1.89 eV) ex14 (2.08 eV)

Frauenfelder's diffusivity

9th international Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Salamanca, 2-3 June 2008 © Gasparyan Yury

Modeling of IDP

0 2 4 6 8 10 120.0

0.5

1.0

1.5

2.0

ga

s o

ff

be

am

off

Pe

rme

atio

n fl

ux,

10

14x

D/m

2 sec

Time, 103 x sec

experiment TMAP 7 DLR formula

be

am

& g

as

on

• Good agreement in assumption of uniformly distributed defects with detrapping energy of Et = (2.05±0.15) eV and the concentration of 1-20 ppm• GDP gives (S×D) ~ 10*(S×D)Fr

Experimental detailsT = 893 K PD2 = 7.7×10-4 Pa Finc = 0.36×2.0×1017 D/m2sec

Variable parameters: Et = 2.0 eV nt = 16.5 ppm Krec= 3.4×10-21 m4/secKd = 2.9×1018 1/m2/Pa

9th international Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Salamanca, 2-3 June 2008 © Gasparyan Yury

TDS setup

Setup for TDS measurements with fast loading.

Base pressure: <10-7 Pa. Linear heating up to 1700 K.

sample

9th international Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Salamanca, 2-3 June 2008 © Gasparyan Yury

TDS after gas exposure

• Exposure to D2 at 10-3 Pa for 1 hour at T=873 K in TDS chamber

• The sample was moved out to another chamber; TDS chamber was baked out for the night

• The hot region was annealed to the maximal temperature

• TDS measurements 400 600 800 1000 1200 14000.0

0.5

1.0

1.5

2.0

De

sorp

tion

ra

te, 1

012*D

/se

cTemperature, K

Y

• Deuterium release starts from 850 K (~exposure temperature) with a peak at 1000 K. One can expect that the activation energy is rather high.

• Release after 1200 K (HD signal) was attributed to background

9th international Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Salamanca, 2-3 June 2008 © Gasparyan Yury

Calculations

600 700 800 900 1000 1100 1200 13000.0

0.5

1.0

1.5

2.0

2.5 E

t=1.7 eV n

t=5e-2 %

Et=1.9 eV n

t=5e-3 %

Et=2.1 eV n

t=1e-3 %

Et=2.1 eV n

t=5e-4 %

Et=2.3 eV n

t=1e-4 %

Et=2.3 eV n

t=5e-5 %

experiment

Des

orpt

ion

rate

, 1015

1/m

2 s

Temperature, K

• Frauenfelder’s value for diffusivity and solubility

• Uniform distribution of defects

• Saturation of the sample

• Equilibrium between trapped and dissolved deuterium

• Different combination of trap concentration and binding energy can give same position of peak.

•Lower binding energies need unrealistically high concentrations of defects and give low amplitude.

•The detrapping energy above 2.0 eV should be considered.

9th international Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Salamanca, 2-3 June 2008 © Gasparyan Yury

TDS after plasma exposure

400 600 800 1000 1200

1

2

3

4

5

Des

orpt

ion

rate

, 10

17 D

/m2 s

Temperature, K

RF discharge, 50 m W

unannealed, polished annealed (30 min at 1700 K),

polished

400 600 800 1000 12000.0

0.1

0.2

0.3

0.4

0.5

Des

orpt

ion

rate

, 10

17 D

/m2s

Temperature, K

RF discharge, 50 m W

Particles: mainly D3+

(D3+- 72,5%, D2

+- 21%, D+- 6,5%)Energy: 300 eVTemperature: 330 KFlux: 1020 D/m2secFluence: 3.5×1022 D/m2

• Most part of deuterium desorbed until 800 K

• One can see the peak at 1000 K for both annealed and unannealed samples

• Annealing decrease retention significantly at such fluences

9th international Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Salamanca, 2-3 June 2008 © Gasparyan Yury

High temperature defects

A. van Veen, et al., J. Nucl. Mater. 155-157 (1988) 1113-1117

Vacancies:

Et = 1.4-1.5 eV

Decoration of voids:

Et = 1.8-2.1 eV

• Uniformly distributed in the bulk voids can be a case of our experiment• Voids can be formed during “rolling” process as well as during annealing at 900 K • Vacancies cluster formation during annealing at such temperatures was observed in H. Eleveld (J. Nucl. Mater. 212-215 (1994) 1421-1425)

9th international Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Salamanca, 2-3 June 2008 © Gasparyan Yury

Summary

• Uniformly distributed defects with detrapping energy of ~ 2 eV and concentration of 1-20 ppm can explain both IDP and TDS experimental results

• The existence of the high energy defects can increase the tritium inventory at high temperatures and make problems for tritium removal

• This defects were attributed to small voids or vacancies clusters

• Estimated concentration is small, but these clusters can be centers of bubbles formation

9th international Workshop on Hydrogen Isotopes in Fusion Reactor Materials, Salamanca, 2-3 June 2008 © Gasparyan Yury

PSI 2008

• D.Nunes(P3-47). SEM of the tungsten probe cross section after exposition in tokamak. 10-30 μm bubbles on grain boundaries were observed

• R.A.Causey(P3-69). 2 mm Plansee tungsten annealed at 1273K and exposed to high deuterium fluences. SEM and TEM don’t detect bubbles. < 2 nm bubbles could not be detected.

• N.Yoshida(I-18). Bubbles formation after neutron irradiation at 600C

• Bubbles are formed after exposure to helium plasma

• G.M.Wright(P1-65). Deuterium retention after deuterium exposure at 1000 C.

• O.Ogorodnikova(J.Appl. Phys., 2008). TDS after 200 eV ion exposure at 773 K, peak at 1100 K; 2.1 eV was used in calculations