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 and Gon-Ho Kim Plasma Application Laboratory (http://pal.snu.ac.kr) Energy Systems Engineering, Seoul National University Plasma Seoul National University Application Department of Nuclear Engineering Laboratory
Research Background [2] [3] Melting Surface deformation of spray coated W [2] [4] Cracking Blistering Design apparatus of ITER divertor with full tungsten PFCs [1] Morphological changes of tungsten in high heat & ion flux condition Surface deformation by fusion plasma ⇒ Key factor for erosion and retention issues 1
Objectives of Research Deformation of W PFCs by Fusion Plasma Ion damages Thermal damages High density plasma High power thermal source : ECR plasma : ECR plasma : Thermal plasma torch : Thermal plasma torch Surface morphological change Surface morphological change Variation of Surface and bulk properties Variation of Surface and bulk properties - blister , bubbling, roughening - blister , bubbling, roughening - recrystallization , melting - recrystallization , melting roughening, cracking , roughening, cracking , Synergetic Effect with ion and thermal fluxes Synergetic Effect with ion and thermal fluxes • • Understand the morphological variation of Tungsten as PFCs Understand the morphological variation of Tungsten as PFCs • • Estimate the erosion property and lifetime of PFCs in Fusion Reactor Estimate the erosion property and lifetime of PFCs in Fusion Reactor 2
1D SOL Simulator and Thermal Loader Micro D 2 inlet wave Coolant T.C. gauge Pyrometer T.C. N 2 / Ar Target Target Coolant Coolant Turbo A pump T.C. ≤300 A DC Mode Pulse Mode R B C 0 Heat exchanger R.P. < 300 Switch < 3 kV V Device Thermal Flux Device Plasma Characteristics Thermal Loader n e ~ 2 × 10 17 m -3 , T e ~ 5 eV, Ion Irradiator ≤ ~ 10 MW/m 2 (Plasma torch) Γ i ~ 3.09 × 10 21 m -2 s -1 (ECR source) KSTAR divertor [6, 7] 3.5 ~ 4.5 MW/m 2 n e ~ 2.5 × 10 17 m -3 , T e ~ 4 eV, KSTAR SOL [5] Γ i ~ 3.46 × 10 21 m -2 s -1 ITER divertor [6, 7] 5 ~ 20 MW/m 2 3
Results 1. : Recrystallization of Bulk W with Energy Dose Increase energy dose 1440 MJ/m 2 (12 MW/m 2 , 120 s) 2100 MJ/m 2 (5 MW/m 2 , 420 s) 3000 MJ/m 2 (12 MW/m 2 , 250 s) Pristine Recrystallization Surface roughening Grain growth Crack formation Crack growth 2 μ m 2 μ m 2 μ m 2 μ m 400 nm 400 nm 400 nm 400 nm 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 4
Results 1. : Acceleration of Deformation with PS-W Energy dose = 2100 MJ/m 2 (Thermal load, 5 MW/m 2 , 7 min) Surface temperature ≥ 1700 ℃ Recrystallization 1) Thickness of recrystallized layer Recrystallization layer layer Bulk-W (10 μ m) < PS-W (40 μ m) : Increase of surface temperature of PS-W due to its low thermal conductivity 10 μ m 10 μ m 2) Diameter of nano bubble Cross section View – Bulk W Cross section View – W Coating Bulk-W (100 nm) < PS-W (2 μ m) : Acceleration of bubble generation by μ m-sized pore inside the PS-W (which is generated during fabrication) 3) Width of crack Bulk-W (100 nm) < PS-W � 500 nm) : Increase of crystal size due to high surface temperature of PS-W Top View – Bulk W Top View – W Coating 2 μ m 2 μ m 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 operation 5
Results 1. : Deformed Thickness with Energy Dose 2200 Bulk W W coating PS - W ~ 21 W/m-K 2000 Grain growth rate [cm 2 /sec] Graphite base 100 W/m-K ] ℃ Temperature [ 1800 Re-crystallization temp. 1600 Bulk W 1400 117 W/m-K Re-crystallization Layer thickness 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 2400 2200 2000 1800 1600 1400 Temperature [ ℃ ] Position from bottom [mm] Temperature evaluation of bulk W and PS - W along the substrate axis Growth rate of tungsten with temperature [8] Heat flux ↑ ⇒ Surf. Temp.↑ ⇒ Grain growth rate↑ Energy dose ↑ Deformed thickness ↑ Time ↑ ⇒ Annealing time ↑ 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 6
Results 2. : Issues in Formation and Growth of Blister in W Growth phase of blister [8] No blister Group of blister Site of formation 2 μ m Merging of blisters Growth mechanism Merging Size growing Side bursting Bursting & After phase 400 nm 7
Results 2. : Blister Growth Characteristics with Energy Dose Increase energy dose 80 MJ/m 2 (100 eV, 4.98 x 10 24 m -2 ) 159 MJ/m 2 (100 eV, 9.96 x 10 24 m -2 ) 318 MJ/m 2 (100 eV, 1.99 x 10 25 m -2 ) 768 MJ/m 2 (100 eV, 4.80 x 10 25 m -2 ) 2 μ m 2 μ m 2 μ m 2 μ m Blister merging Traces of full bursting Re-formation of 2 nd Blister Side Bursting Growth of 2 nd Blister 400 nm 400 nm 400 nm 400 nm Re-formation of 2 nd Blister after full bursting Growth of 2 nd blister Blister formation & growth Bursting 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 2 nd blister is generated in trace of full bursting and enlarged with increment of energy dose Cross section 8 of re-formed 2 nd blister
Results 2. : Temperature Effect for Blister 100 eV Ion irradiation with additional surface heating by microwave 158 MJ/m 2 (100 eV, 0.99 x 10 25 m -2 ) 633 MJ/m 2 (100 eV, 3.96 x 10 25 m -2 ) Grain growth Grain growth 2 μ m 2 μ m Growth of 2 nd blister Re-formation seed of 2 nd blister 400 nm 400 nm 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/m 2 . Re-formation seed is generated in the trace of full bursting for 2 nd blister. 2 nd blister is enlarged with similar shape of crystal grain growth 9
Results 3. : Synergetic Effect with ion and Thermal fluxes 3000 MJ/m 2 (12 MW/m 2 , 250 s) 633 MJ/m 2 (100 eV, 3.96 x 10 25 m -2 ) 3000 MJ/m 2 (12 MW/m 2 , 250 s) Crack growth 2 μ m 2 μ m 400 nm 400 nm Simulation of simultaneous ion and thermal load on bulk W Thermal load on ion irradiated W - D Ion (633 MJ/m 2 ) + Thermal load (2100 MJ/m 2 ) Smaller grains are formed with more clean surface on the ion and thermal loaded bulk W 10
Results 3. : Synergetic Effect on PS - W 20 μ m Ion Dose : 192 MJ/m 2 Cross section View – pristine Cross section View 20 μ m ( 100eV, 1.2 x 10 25 m -2 ) Thermal load : 2100 MJ/m 2 (Thermal load, 5 MW/m 2 , 7 min) 4 μ m 4 μ m Top View – pristine Top View Simulation of simultaneous ion and thermal load on PS - W Thermal load on ion irradiated W (in SNU) - D Ion (192 MJ/m 2 ) + Thermal load (2100 MJ/m 2 ) Needle-like recrystallization is observed on the top surface of PS-W with thickness of 30 μ m 11
Deformation of Tungsten PFCs with Energy Dose Deformed Crack growth thickness Thick layer Growth of 2 μ m After phase of Reformation blister Reformation full bursting of blister 400 nm Thermal 400 nm Effect ? Grain growth Recrystallization & cracking at Surface Growth Bursting Formation of blister of blister of blister 2 μ m 2 μ m 400 nm 400 nm 400 nm Energy 10 6 J/m 2 10 7 J/m 2 10 8 J/m 2 10 9 J/m 2 10 10 J/m 2 Dose 12
Summary & Future Works • Summary Tungsten PFCs are damaged by high thermal load with deformation procedure f rom 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 2 nd 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 μ m • 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 2 nd blister. 13
References & Comments • References [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) • Comments 14
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