Modelling of ion - driven deuterium retention in W
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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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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

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


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


Ion implantation and TDS

TDS shows two peaks.

Both peaks grow with fluence.

Second peak (high-temperature) grows faster.


Ion implantation and TDS

Pre-implantation with intermediate TDS increases the second peak.


Modelling of D retention in PCW

Desorption, J0

trapping

Implantation, I0

Permeation, JL


Modelling of D retention in PCW

Ion-induced traps

Natural traps

Desorption, J0

trapping

Implantation, I0

Permeation, JL


Dislocations,

Grain boundaries

Bubbles, Vacancies

Modelling of D retention in PCW

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


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)


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)


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)


Modelling of D retention in PCW

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


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


Modelling of D retention in PCW

  • Why D agglomerates in clusters only near the implantation surface? =>

  • Because of stress field induced by ion implantation


=>

=>

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


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


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.


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.


Implantation energy effect

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


Implantation energy effect

Increase of the stress field =>

increase of the diffusion coefficient


Implantation energy effect

Increase of the stress field =>

increase of the diffusion coefficient


Implantation energy effect

Calculated depth profiles

Increase of the stress field =>

increase of the diffusion coefficient


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



Implantation energy effect

Increase of the stress field =>

increase of the diffusion coefficient


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.


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


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.


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


Deuterium retention in W

W: 3 keV D+, RT


  • 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


Implantation energy effect

Increase of the stress field =>

increase of the diffusion coefficient


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


    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


    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


    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


    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


    Talk outline

    • Experimental data

    • Modelling of D retention in PCW

      • Temperature effect

      • Implantation history effect

      • Ion energy effect


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