Failure and Development VDE Simulator using Transferred Arc Torch - - PowerPoint PPT Presentation

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Plasma Application Laboratory

Seoul National University

Department of Nuclear Engineering

Investigation of High Current Induced PFC Interlayer Failure and Development VDE Simulator using Transferred Arc Torch

KSTAR Conference and Fusion Science Workshop, Muju, Feb 24-26, 2014

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

Department of Energy Systems (Nuclear) Engineering, Seoul National University, Seoul 151-741, Korea

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Seoul National University

Department of Nuclear Engineering

Plasma Application Laboratory

Vertical Displacement Event in Tokamaks

[1] ITER physics expert group on disruption, Nucl. Fusion 39. 2251. (1999).

[1] Thermal quenching [high heat flux] Current quenching [Halo current] JhaloxB damage Runaway electron damage

• Halo current at VDE
• ITER : ~ 8 MA (limitation)
• JET : ~ 3.5 MA
• ASDEX : ~ 700 kA

Heat flux : ~ GW/m2 Current flux : 20 ~ 200 MA/m2 During VDE

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Seoul National University

Department of Nuclear Engineering

Plasma Application Laboratory

Void Generation by High Current Flux on Heterogeneous Bond [2]

     

R t dt t d J n   

e e e e e e e

Vacancy Intermetallic compound Void



For CW current (Electric device, minor ELM) For Pulse current (major ELM, VDE)

     

c

TTF

d n d t K J t t R



   

 

 

1 m

n J dt n d   



  

 

 

 

 

1

1 1 1 1

DC pulse DC a D D a a

MTTF MTTF e e D a e D

    

             Time to failure (TTF) is a function of current flux, J(t) and background void character, R(δ)

• Void relaxation factor

 Higher temperature, pulse duration in Tokamak case

[2] J. Tao, et. Al., Phys. Symp., pp. 338-343. (1992),

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Seoul National University

Department of Nuclear Engineering

Plasma Application Laboratory

Interlayer Void Formation Effect on PFC Life Time

[3] [4]

[3] Miyazaki, T. et el., Microelectronics Reliablity, Vol. 46,pp. 1898-1903, (2006). [4] R. Mitteau, 5rd Karlsruhe International school on fusion technol.

• IGBT bridge joint (~ MA/m2), 180 oC
• High current flux [> MA/m2] enhance heterogeneous bond material diffusion 

intermetallic compound formation  void generation

• Void transient to interlayer crack by thermal stress at the heterogeneous bond vicinity

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Seoul National University

Department of Nuclear Engineering

Plasma Application Laboratory

Experimental Setup for Simulate Current Quench on PFC

• 0.50
• 0.25

0.00 0.25 0.50 2000 4000 6000 8000

Current [A] Time [msec] Pulse current profile

A

W Cu W C

I

Pulse high current ~ 10 kA ~ 200 μsec (1/10 of current quench time) W Graphite

Pulse I

Current flux : 0.1, 1 GA/m2 Cycle : 100 cycle (10 cycle of VDE)

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Seoul National University

Department of Nuclear Engineering

Plasma Application Laboratory

Heterogeneous Bond Fracture by Current Quench : W-Graphite

Pristine 0.1 GA/m2 1 GA/m2 Graphite Tungsten Titanium Graphite Graphite Tungsten Tungsten Titanium Titanium X 1k

• High current flux induced W-Ti-Graphite blazed specimen in room temperature condition
• Bond material (Ti) diffusion is observed

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Seoul National University

Department of Nuclear Engineering

Plasma Application Laboratory

Heterogeneous Bond Fracture by Current Quench : W-Cu

Pristine 0.1 GA/m2 1 GA/m2

• High current flux induced W-Cu blazed specimen in room temperature condition
• Only current quenching condition of VDE is simulated and thermal quenching simulator

development is in progress

X 1k X 5k

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Seoul National University

Department of Nuclear Engineering

Plasma Application Laboratory

Transferred Arc Plasma Characteristics : SNU-PAL

60 80 100 120 140 30 40 50 60 70

transferred plasma method

Voltage [V] Current [A]

• Arc spot characteristic
• Heat flux : ~ 1 GW/m2
• Current flux : ~ 1 GA/m2

~ 300 A, 10 kW Arc operation current-power Anode spot : anode surface Arc cathode Arc anode

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Seoul National University

Department of Nuclear Engineering

Plasma Application Laboratory

Thermal and Current Quench Simulator Development by Swept Arc Spot

   

19 22 3 3 9 2

1.6 10 10 #/ 5 10 / 0.8 80 10 / C m V m E B mTesla G J A m 



     

To diffract 45o,

electric force Lorentz

F F 

• Force balance for arc sweep

Auxiliary pulse magnetic field Target Arc spot swept by auxiliary pulse B-field

• ~ GW/m2, GA/m2 spot sweep

( ) F e E v B f E J B        

ρ = 1022 #/m3 E = ~ 5x103 V/m J = 109 A/m2 Required auxiliary B-field

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Seoul National University

Department of Nuclear Engineering

Plasma Application Laboratory

Design of Pulse Magnetic Field Coil for Arc swift

• Auxiliary magnetic field coil design

1 kA

• Pulse magnetic field measurement
• 20

20 40 60 80 100 20 40 60 80

B-field [G] Time [sec] Pulse magnetic field

Auxiliary coil B-dot probe

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Seoul National University

Department of Nuclear Engineering

Plasma Application Laboratory

Summary

• Current quench damage on PFC is simulate by pulse current source

: 0.1, 1 GA/m2, 200 μsec 100 cycle in room temperature condition to evaluate PFC damage on ITER VDE condition

• Bond material (Ti) diffusion is observed in W-Ti-Graphite specimen and

analysis the effect of electro-migration on material diffusion is in progress

• In particular W-Cu intermetallic compound is not observed in 0.1, 1 GA/m2

flux, 200 μsec pulse 100 cycle in room temperature.

• Thermal and current quench simulator development using transferred arc

torch facility in progress

• Auxiliary magnetic coil is designed and coil installation in transferred arc

torch is in progress