Effect of Thermal Loading with D 2 Ion Irradiation on Surface - - PowerPoint PPT Presentation

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KSTAR Conference 2014 (24-26 February, 2014, Mayhills Resort, Gangwon-do, Korea) P- 42 Effect of Thermal Loading with D 2 Ion Irradiation on Surface Deformation of PFC Tungsten Hyun-Su Kim Younggil Jin, Sun-Taek Lim, Jin Young Lee, Jae-Min Song

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Plasma Application Laboratory

Seoul National University

Department of Nuclear Engineering

Effect of Thermal Loading with D2 Ion Irradiation

  • n Surface Deformation of PFC Tungsten

KSTAR Conference 2014 (24-26 February, 2014, Mayhills Resort, Gangwon-do, Korea)

P- 42

Hyun-Su Kim Younggil Jin, Sun-Taek Lim, Jin Young Lee, Jae-Min Song and Gon-Ho Kim

Plasma Application Laboratory (http://pal.snu.ac.kr) Energy Systems Engineering, Seoul National University

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Research Background

Morphological changes of tungsten in high heat & ion flux condition Design apparatus of ITER divertor with full tungsten PFCs[1]

  • Surface deformation by fusion plasma

⇒ Key factor for erosion and retention issues

[2] [2] [3] [4] Melting Surface deformation

  • f spray coated W

Cracking Blistering

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2

: ECR plasma Surface morphological change

  • blister, bubbling, roughening

: ECR plasma Surface morphological change

  • blister, bubbling, roughening

High density plasma

: Thermal plasma torch Variation of Surface and bulk properties

  • recrystallization, melting

roughening, cracking, : Thermal plasma torch Variation of Surface and bulk properties

  • recrystallization, melting

roughening, cracking,

High power thermal source

Objectives of Research

Ion damages

Deformation of W PFCs by Fusion Plasma

Thermal damages

  • Understand the morphological variation of Tungsten as PFCs
  • Estimate the erosion property and lifetime of PFCs in Fusion Reactor
  • Understand the morphological variation of Tungsten as PFCs
  • Estimate the erosion property and lifetime of PFCs in Fusion Reactor

Synergetic Effect with ion and thermal fluxes Synergetic Effect with ion and thermal fluxes

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1D SOL Simulator and Thermal Loader

Device Plasma Characteristics Ion Irradiator (ECR source) ne ~ 2 × 1017 m-3, Te ~ 5 eV, Γi ~ 3.09 × 1021 m-2s-1 KSTAR SOL [5] ne ~ 2.5 × 1017 m-3, Te ~ 4 eV, Γi ~ 3.46 × 1021 m-2s-1 Device Thermal Flux Thermal Loader (Plasma torch) ≤ ~ 10 MW/m2 KSTAR divertor [6, 7] 3.5 ~ 4.5 MW/m2 ITER divertor [6, 7] 5 ~ 20 MW/m2

Micro wave D2 inlet Turbo pump Target

< 300 V

DC Mode Pulse Mode

RB Switch C0

< 3 kV

A

Coolant Coolant N2 / Ar Coolant

Heat exchanger

R.P. ≤300 A

T.C. T.C.

T.C. gauge Pyrometer Target

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2 μm 2 μm

Results 1. : Recrystallization of Bulk W with Energy Dose

1440 MJ/m2 (12 MW/m2, 120 s) 2100 MJ/m2 (5 MW/m2, 420 s) 3000 MJ/m2 (12 MW/m2, 250 s) Pristine

2 μm 2 μm 400 nm 400 nm 400 nm 400 nm

Increase energy dose

Surface roughening Grain growth Recrystallization Crack formation Crack growth

  • Temperature of thermal irradiated surface ~ 1700 ℃
  • Deformation of tungsten surfaces are proceeded from grain growth and roughening to recrystallization and

cracking as energy dose increase

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5 Top View – W Coating

2 μm

Cross section View – W Coating

10 μm

Recrystallization layer Top View – Bulk W

2 μm

Cross section View – Bulk W Recrystallization layer

10 μm

1) Thickness of recrystallized layer 2) Diameter of nano bubble 3) Width of crack Bulk-W (10 μm) < PS-W (40 μm) Bulk-W (100 nm) < PS-W (2 μm) Bulk-W (100 nm) < PS-W 500 nm)

: Acceleration of bubble generation by μm-sized pore inside the PS-W (which is generated during fabrication) : Increase of surface temperature of PS-W due to its low thermal conductivity : Increase of crystal size due to high surface temperature of PS-W

  • Classification of W PFC damage by divertor thermal load (ITER steady-state standard) :

1) Thickness of recrystallized layer, 2) Diameter of nano bubble, 3) Width of crack

  • PS-W can be used for the simulation of aged bulk-W which is expected after accumulated damage during
  • peration
  • Energy dose = 2100 MJ/m2 (Thermal load, 5 MW/m2, 7 min)
  • Surface temperature ≥ 1700 ℃

Results 1. : Acceleration of Deformation with PS-W

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  • Deformed thickness of W is enlarged as increment of energy dose
  • PS-W shows higher temperature of surface and thicker deformed layer than those of bulk W

Results 1. : Deformed Thickness with Energy Dose

Growth rate of tungsten with temperature[8] Grain growth rate [cm2/sec] 2400 2200 2000 1800 1400 1600 Temperature [℃] 0.5 0.4 0.3 0.2 0.1 0.0

  • 0.1

1400 1600 1800 2000 2200

Temperature [ ] ℃ Position from bottom [mm] Bulk W PS - W

Graphite base 100 W/m-K W coating ~ 21 W/m-K Bulk W 117 W/m-K Re-crystallization Layer thickness Re-crystallization temp. Temperature evaluation of bulk W and PS - W along the substrate axis

Heat flux↑ ⇒ Surf. Temp.↑ ⇒ Grain growth rate↑ Time ↑ ⇒ Annealing time ↑ Energy dose↑ Deformed thickness ↑

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Results 2. : Issues in Formation and Growth of Blister in W

Growth phase of blister[8]

Site of formation Growth mechanism Merging Size growing Bursting & After phase

400 nm 2 μm

No blister Group of blister Side bursting Merging of blisters

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  • Blisters are formed at low energy dose phase, and grown with merging.
  • Blisters are burst and destroyed in high energy dose
  • Grain oriented re-formation of 2nd blister is generated in trace of full bursting and

enlarged with increment of energy dose

Results 2. : Blister Growth Characteristics with Energy Dose

768 MJ/m2 (100 eV, 4.80 x 1025 m-2)

Increase energy dose

318 MJ/m2 (100 eV, 1.99 x 1025 m-2) 159 MJ/m2 (100 eV, 9.96 x 1024 m-2) 80 MJ/m2 (100 eV, 4.98 x 1024 m-2) Bursting Growth of 2nd blister

2 μm 2 μm 2 μm 2 μm 400 nm

Blister formation & growth Blister merging

400 nm

Side Bursting

400 nm

Re-formation of 2nd Blister Traces of full bursting

400 nm

Re-formation of 2nd Blister after full bursting

Cross section

  • f re-formed 2nd blister

Growth of 2nd Blister

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Results 2. : Temperature Effect for Blister

2 μm

633 MJ/m2 (100 eV, 3.96 x 1025 m-2)

Grain growth

400 nm

Growth of 2nd blister

  • 100 eV Ion irradiation with additional surface heating by microwave

Re-formation seed

  • f 2nd blister

400 nm 2 μm

158 MJ/m2 (100 eV, 0.99 x 1025 m-2)

Grain growth

  • Grains are grown at the elevated surface temperature ~ 1400 ℃ by microwave
  • Full bursting of blister is occurred at low energy dose condition of 158 MJ/m2.
  • Re-formation seed is generated in the trace of full bursting for 2nd blister.
  • 2nd blister is enlarged with similar shape of crystal grain growth
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Results 3. : Synergetic Effect with ion and Thermal fluxes

3000 MJ/m2 (12 MW/m2, 250 s)

2 μm

Crack growth

400 nm 400 nm 2 μm

633 MJ/m2 (100 eV, 3.96 x 1025 m-2) 3000 MJ/m2 (12 MW/m2, 250 s)

  • Simulation of simultaneous ion and thermal load on bulk W

Thermal load on ion irradiated W - D Ion (633 MJ/m2) + Thermal load (2100 MJ/m2)

  • Smaller grains are formed with more clean surface on the ion and thermal loaded bulk W
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Results 3. : Synergetic Effect on PS - W

Cross section View – pristine

20 μm

Cross section View

20 μm

Top View – pristine

4 μm

Top View

4 μm

Ion Dose : 192 MJ/m2 ( 100eV, 1.2 x 1025 m-2) Thermal load : 2100 MJ/m2 (Thermal load, 5 MW/m2, 7 min)

  • Simulation of simultaneous ion and thermal load on PS - W

Thermal load on ion irradiated W (in SNU) - D Ion (192 MJ/m2) + Thermal load (2100 MJ/m2)

  • Needle-like recrystallization is observed on the top surface of PS-W with thickness of 30 μm
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Deformation of Tungsten PFCs with Energy Dose

Deformed thickness

Energy Dose 109 J/m2 107 J/m2 106 J/m2

at Surface Thick layer

400 nm

Formation

  • f blister

2 μm

Grain growth

2 μm

Recrystallization & cracking 1010 J/m2 108 J/m2 After phase of full bursting 400 nm 400 nm 400 nm Growth

  • f blister

400 nm Bursting

  • f blister

Reformation

  • f blister

Growth of Reformation blister 2 μm Crack growth

Thermal Effect ?

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Summary & Future Works

  • Tungsten PFCs are damaged by high thermal load with deformation procedure from grain growth and

roughening to recrystallization and cracking as energy dose increase.

  • PS-W shows more severe deformation with larger thickness of deformed layer and crack width than

those of bulk W. (pre-damaged / aged effect)

  • Blisters are formed and grown at low energy dose phase, in high energy dose, blisters are destroyed with

bursting which provides re-formation seed of 2nd blister in its trace.

  • Ion irradiated tungsten represents smaller grain with more clean surface, whereas Needle-like

recrystallization is observed on the top surface of ion irradiated PS-W with thickness of 30 μm

  • Summary
  • Future works
  • Quantitative correlation of thermal energy dose and deformed layer is further studied with

considering ion irradiation effect and surface temperature

  • Further data of blister formation are achieved for the understanding of formation, growing, and re-

formation of 2nd blister.

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References & Comments

[1] T. Hirai, et al., Fusion Engineering and Design, 88, 1798 (2013) [2] F.L. Chong, et al., Journal of Nuclear Materials, 386–388, 780 (2009) [3] L. Xiang, et al., Plasma Science & Technology, 5, 1887 (2003) [4] K. Tokunaga, et al., Journal of Nuclear Materials, 307–311, 126 (2002) [5] J. G. Bak et al., Contrib. Plasma Phys. 53, 69 (2013) [6] T. Hirai, et al., Material Transactions, 46, 412 (2005) [7] B. Lee, et al., Fusion Sci. Technol., 37, 110 (2000) [8] D. William, et al., NASA Technical Note, D-3232 (1966)

  • References
  • Comments