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Modelling of ion - driven deuterium retention in W O.V. Ogorodnikova in collaboration with J. Roth and M. Mayer MPI für Plasmaphysik, EURATOM Association, Garching, Germany. Ion implantation and TDS. D retention in W has been studied in ion beam experiments: monoenergetic ion beam

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slide1

Modelling of ion - driven deuterium retention in W

O.V. Ogorodnikova

in collaboration with

J. Roth and M. Mayer

MPI für Plasmaphysik, EURATOM Association, Garching, Germany

slide2

Ion implantation and TDS

D retention in W has been studied in ion beam experiments:

monoenergetic ion beam

E = 200 eV D+ to 3 keV D+

T = 300 K to 600 K

D inventory in W increases as a square root of fluence at RT => diffusion-limited trapping.

Ogorodnikova O.V., Roth J., Mayer M., J. Nucl. Mater. 313-316 (2003) 469-477

slide3

Ion implantation and TDS

D retention in W has been studied in ion beam experiments:

monoenergetic ion beam

E = 200 eV D+ to 3 keV D+

T = 300 K to 600 K

D inventory in W increases as a square root of fluence at RT => diffusion-limited trapping.

Most of D are trapped in the bulk at high fluences.

Ogorodnikova O.V., Roth J., Mayer M., J. Nucl. Mater. 313-316 (2003) 469-477

slide4

Ion implantation and TDS

TDS shows two peaks.

Both peaks grow with fluence.

Second peak (high-temperature) grows faster.

slide5

Ion implantation and TDS

Pre-implantation with intermediate TDS increases the second peak.

slide6

Modelling of D retention in PCW

Desorption, J0

trapping

Implantation, I0

Permeation, JL

slide7

Modelling of D retention in PCW

Ion-induced traps

Natural traps

Desorption, J0

trapping

Implantation, I0

Permeation, JL

slide8

Dislocations,

Grain boundaries

Bubbles, Vacancies

Modelling of D retention in PCW

Diffusion model with two kinds of traps describes well experimental data.

slide9

Modelling of D retention in PCW

0.85 eV

1.45 eV

Ion-induced traps distributes near the surface and natural traps distributes along whole W thickness

W(x,t)=Wm(1 – exp(-(1-r)I0y(x)ht/Wm))

Rate of defect production h = f (initial traps, ion flux, ion energy, temperature)

slide10

Dislocations,

Grain boundaries

Bubbles, Vacancies

Modelling of D retention in PCW

Ion-induced traps distributes near the surface and natural traps distributes along whole W thickness

W(x,t)=Wm(1 – exp(-(1-r)I0y(x)ht/Wm))

Rate of defect production h = f (initial traps, ion flux, ion energy, temperature)

slide11

Modelling of D retention in PCW

Rate of defect production is higher for pre-implantation with intermediate TDS

Ion-induced traps distributes near the surface and natural traps distributes along whole W thickness

W(x,t)=Wm(1 – exp(-(1-r)I0y(x)ht/Wm))

Rate of defect production h = f (initial traps, ion flux, ion energy, temperature)

slide12

Modelling of D retention in PCW

Ion-induced traps distributes near the surface and natural traps distributes along whole W thickness

slide13

Modelling of D retention in PCW

  • Which kinds of ion-induced defects of 1.45 eV can be produced by low energy ions? =>
  • - 200 eV cannot produce vacancies (Eth=860 eV)
  • - D self-aggregation in clusters due to stress field created by implanted deuterium
slide14

Modelling of D retention in PCW

  • Why D agglomerates in clusters only near the implantation surface? =>
  • Because of stress field induced by ion implantation
slide15

D agglomeration in clusters and bubble growth

=>

=>

Tension and stress=>

Displacement of W atom=>

Di-vacancy=>

Bubble growth

D traps by vacancy

Several D trap by vacancy

Tension and stress=>

Dislocation (loop punching?)

  • Conditions for bubble formation:
  • Saturation in D concentration
  • Saturation in vacancies
slide16

Temperature effect

An increase of the temperature results in a decrease of D retention for recrystallized ´virgin´ PCW

At 400 K D retention increases with fluence faster than at RT

slide17

Temperature effect

D retention decreases with temperature for ´virgin´ W

An increase of the temperature results in a decrease of D retention

for recrystallized ´virgin´ PCW

Model describes well temperature dependence.

slide18

Temperature effect

D retention decreases with temperature for ´virgin´ W.

Most of D are in the bulk.

An increase of the temperature results in a decrease of D retention

for recrystallized ´virgin´ PCW

Model describes well temperature dependence.

slide19

Implantation energy effect

Lower D retention for 3 keV than for 200 eV at high fluences

slide20

Implantation energy effect

Increase of the stress field =>

increase of the diffusion coefficient

slide21

Implantation energy effect

Increase of the stress field =>

increase of the diffusion coefficient

slide22

Implantation energy effect

Calculated depth profiles

Increase of the stress field =>

increase of the diffusion coefficient

slide23

Conclusions

  • D retains in W in ion-induced defects and natural defects
  • An increase of ion energy (or/and ion flux) results in an increase of the stress field in the implantation region. As a result the diffusion coefficient near the implantation region increases.
  • Both no recrystallization and intermediate TDS (annealing up to 1200 K) increase the rate of defect production

Ion-induced defects are produced during implantation by deuterium self-aggregation due to the stress field induced by the incident ion flux

The rate of ion-induced defect production depends on the energy of the incident ions, ion flux, sample temperature and initial trap concentration

slide25

Implantation energy effect

Increase of the stress field =>

increase of the diffusion coefficient

slide26

Implantation history effect

D retention decreases with temperature for ´virgin´ W.

D retention has a maximum for

re-used W.

An increase of the temperature results in a decrease of D retention

for recrystallized ´virgin´ PCW

Model describes well temperature dependence.

slide27

Implantation history effect

Recrystallized W

As-received W after multiple implantation

D retention in the second peak decreases with temperature

for recrystallized W

D retention in the second peak increases with temperature for re-used W

slide28

Implantation history effect

Intermediate TDS increases the amount of initial high-temperature traps

Calculations using the higher rate of defect production are in a good agreement with experiments.

An increase of the temperature results in a decrease of D retention

for recrystallized ´virgin´ PCW

Model describes well temperature dependence.

slide29

Modelling of D retention in PCW

  • The increase of amount of initial traps increases the rate of deuterium cluster formation
  • Both intermediate TDS and no recrystallization increase the amount of initial traps
slide30

Deuterium retention in W

W: 3 keV D+, RT

slide31

Conditions for cluster formation and bubble growth

  • Conditions for cluster formation in W
  • Initial amount of defects
  • Low solubility and diffusivity
  • Low porosity
  • Acceleration of rate of cluster growth
  • High ion flux or/and ion energy
slide32

Implantation energy effect

Increase of the stress field =>

increase of the diffusion coefficient

slide33

R & D

Experiments

          • off-normal events & ELM´s
  • D retention in damage W n-irradiation
          • He-irradiation
  • D retention at high implantation temperature (T=800 K - 1000 K) at different ion fluxes

Modelling

  • Competition of erosion/diffusion
  • Soret effect
  • Maxwellian energy distribution
  • Diffusion in tension field
slide34

Is D retention in W a problem for ITER ?

  • W as a divertor
  • Tplasma: 1-20 eV
  • Particle flux : 1022 – 1024 /m2/s
  • Tw : ~1000 K
  • Competition of erosion/diffusion
  • Deposition of impurities, codeposition ?
  • Damages in the near surface region by off-normal events
  • Diffusion in tension field
slide35

Is D retention in W a problem for ITER ?

  • W as a FW
  • Tplasma: 1-5 eV ?
  • Particle flux : ~1020 /m2/s
  • Tw : ~500 K ?
  • W as a divertor
  • Tplasma: 1-20 eV
  • Particle flux : 1022 – 1024 /m2/s
  • Tw : ~1000 K
  • Temperature of W can be important
  • Diffusion in tension field
  • Competition of erosion/diffusion
  • Deposition of impurities, codeposition ?
  • Damaged by off-normal events near surface region
  • Diffusion in tension field
slide36

Is D retention in W a problem for ITER ?

  • W as a FW
  • Tplasma: 1-5 eV ?
  • Particle flux : ~1020 /m2/s
  • Tw : ~500 K ?
  • W as a divertor
  • Tplasma: 1-20 eV
  • Particle flux : 1022 – 1024 /m2/s
  • Tw : ~1000 K
  • Temperature of W can be important
  • Diffusion in tension field
  • Competition of erosion/diffusion
  • Deposition of impurities, codeposition ?
  • Damaged by off-normal events near surface region
  • Diffusion in tension field
  • Bulk retention can be of concern
slide37

Is D retention in W a problem for ITER ?

  • W as a FW
  • Tplasma: 1-5 eV ?
  • Particle flux : ~1020 /m2/s
  • Tw : ~500 K ?
  • W as a divertor
  • Tplasma: 1-20 eV
  • Particle flux : 1022 – 1024 /m2/s
  • Tw : ~1000 K
  • Temperature of W can be important
  • Diffusion in tension field
  • Competition of erosion/diffusion
  • Deposition of impurities, codeposition ?
  • Damaged by off-normal events near surface region
  • Diffusion in tension field
  • Bulk retention can be of concern
  • n-irradiation – strong trapping in vacancies distributed over all W thickness
slide38

Talk outline

  • Experimental data
  • Modelling of D retention in PCW
    • Temperature effect
    • Implantation history effect
    • Ion energy effect
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