jt-60 sa toroidal field coil structural analysis

Ch. Portafaix 07 April 2009JT-60SA TF magnet structural analyses

AssociationEuratom-CEA

1

JT-60 SA Toroidal Field coil structural analysis

Christophe Portafaix

• Introduction

• TF coil description

• TF coil design and electromagnetic loads

• Material and Criteria

• 2D structural analysis

• 3D structural analysis

• Conclusion



2

Vacuum vessel

Central Solenoid (CS)

Cryostat

Toroidal Field (TF)

coils

Equilibrium Field (EF) coils

~14m

Nominal parameters

Plasma major radius = 2.95 m

Plasma minor radius = 1.18 m

Aspect ratio = 2.5

Plasma current = 5.5 MA

Toroïdal magnetic Field = 2.26 T

Introduction

JT-60SA



3

case

Gravitysupport

18 TF coils

TF coil description Inner leg section

Conductor NbTi6 Double pancakes Temperature 4.4 KCurrent 25.7 kAHe flow rate 4 g/sPeak field 5.65 TTmargin > 1 K



4

TubeTubeInner Inner øø 90mm90mm

Outer Outer øø 140mm140mm

1.5m1.5m

1.4m1.4m

Gravity support

Spherical Joints:Spherical Joints:

Permit to reduce transmitted Permit to reduce transmitted loads (no moment).loads (no moment).

Tube section optimized to Tube section optimized to reduce heat leak.reduce heat leak.



5

Radial net force= 23MN

Wedging of the TF Coils to withstand ‘Centring’ Loads

TF coil design and electromagnetic loads

Wedged

HoopCompression

TF

Coil Contact Areaon Sides

CS

In plane load

Fr and Fz : I ^ Bφ

r

z

Forces caused by TF current and toroidal field



6

T=(1/2) IBρBm=µ0NI/(2πr1)

r1 minimum distance from z axisT=I ρ Bmr1/(2r)

To maintain T constant and no bending moment:ρ=kr with k = 4 πT/(µ0NI2)In plane (z,r), the curve must satisfy the following equation:

[ ] 2/32

2

2

)(11drdz

kdrzd

r +±=

Toroids Forces Winding with constant tension Discussion on thin shell

r

z

Segment of the windingwith local curvature ρ

In plane load Fr and Fz : I ^ Βφ

Bending free : D shape



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Fz =5 MN

Fr= I* <Bphi> =5. MN/m (I=72*25.7kA <Bphi>=5.6/2T )

Fphi=Fr/(2 * sin 10 °) =14.4 MN/m

The centring force is supported by a vault effect in the TF nose (Fphi)

In plane load Fr and Fz : I ^ BφφφφInner leg section

F r

Fz Fphi

• Inner leg wedged

z

r



8

Case: Stainless steel

Inner leg section

Eddy current insulation: glass epoxy

Jacket: Stainless steel

Insulation : glass epoxy

cable

Case cooling channel : stainless steel

Stainless steel: 51% of the inner leg section

NbTi: 4.5% of the inner leg section

SS to withstand Lorentz forces



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Connection of the TF Coils to withstand out of plane loads

N 11 GR 294 97-12-03 W 0.2

IM

NUL

EOB

SOB

SOF

XPF

Out of plane loads Fφφφφ : I ^ Br and Bz

Forces caused by TF current and poloidal field

Structural links have to include an eddy current insulation

Cyclic loads fatigue



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Out of plane loads Fφ φ φ φ : I ^ Br and Bz

• OIS, bolts, keys withstand the Out of plane loads

• Friction between inner leg play an important role in supporting the out of plane loads

OIS

case

z

r

keys

bolts

OIS is separated from the coil casing:

• Simplify the manufacturing

Reduced welding in the coil casing

• Simplify cold testing

• Reduce hoop forces in the bolted connections, thus reducing number of bolt



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Mechanical properties at 4K

0.3%0.5%0.7%0.3%Thermal contraction dl3/l



0.384679Coulomb’s Modulus G13 (GPa)



0.30.30.330.3Poisson’s ratio nu13



1712205Young’s modulus E3 (GPa)



cableResinInsulationEpoxy glass

Stainless steel

1 and 2 along layer direction, 3 perpendicular to layer direction

Material and Criteria



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Stainless steel criteria

Limit stress value: Sm= 547MPa : 2/3 of the yield strength at 4K (820MPa)

• Membrane stress Pm < K*Sm

• Membrane + bending stress < 1.3*K*Sm

Base metal : K=1

Welds : K=1 for plates under 20mm thick

K=0.9 for plates from 20 to 150mm



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Insulation criteria(σn/σ0)+(τn/τ0)

2 < 1 (LHD criteria [1])

σ0: tensile strength at 77K= 38Mpa τ0: shear strength at 77K= 27Mpa

σn: stress perpendicular to the glass fiber

τ n: shear stress

Compressive strength:

600 MPa

[1] Cryogenic shear fracture tests of interlaminar organic insulation for a forced-flow superconducting coil, MT13, Victoria BC, Canada 1993, K. Kitamura et al., NIFS.

-80

-60

-40

-20

0

20

40

60

80

-80 -60 -40 -20 0 20 40

Sig NN (MPa)

Tau

NS

(M

Pa)

ITER criteria static

LHD criteria static

ITER criteria fatigue



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• The calculations are performed in 2D generalised plane strain hypothesis: constant vertical strain corresponding to a verticalforce Fz

Load steps:

1. Cool down from 293K to 4K 2. Cool down + In plane Lorentz forces3. Cool down + In plane Lorentz forces + pressure (quench)

2D structural analysis

Inner leg section



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Magnetic field map in the JT60-SA TF winding pack (T)

Bmax =5.6T

Fr=5. MN/m



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Von Mises Stress map in conductor jacket (MPa).

Maximum von Mises stress = 494MPaRadial displacement (m).

Maximum contact gap distance = 1mm

Load: Cool down + In plane load



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In plane loadNormal stress along the wedge contact.

σn max = 351MPa (compression stress) < 600 MPa Glass epoxy. (limit)



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Cool down + In plane load

Von Mises Stress intensity map in casing.

Maximum Von Misesstress = 447MPa.



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Load: Cool down + In plane load

12

00

=

+

ττ

σσ nn

The LHD criterion for insulation.

σ0: tensile strength at 77K = 38MPa, τ0: shear strength at 77K = 27MPa.σn: stress perpendicular to the glass fiber,τn: shear stress

LHD criteria max = 0.636 < 1



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3D structural analyses

case

OIS

TF coil

CS1

CS2

CS3

CS4

EF3EF2

EF1

EF4 EF5

EF6

FP1

FP2

FP3

FP4

FP5

FP6

TF3

TF2

TF1

TF, CS, EF coils and Plasma



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Electro-magnetic analysis

• In plane forces calculated with TF current only (25.7kA per conductor)

S = 0m S = Smax/2

In Plane Forces (EOB)

1.8

2.3

2.8

3.3

3.8

4.3

4.8

0 2 4 6 8 10 12 14 16 18

s (m)

Mag

net

ic f

orc

e (M

N/m

)

Upper

Inner

Leg

Lower

Inner

LegTF3 TF3’

TF2 TF2’TF1



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Electro-magnetic analysis• Out of plane forces determined

S = 0m S = Smax/2



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Lateral displacementLateral displacement

@ SOF ~ 20mm@ SOF ~ 20mmLocal peak stressLocal peak stress

@ shear panel connection@ shear panel connection



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Max stressMax stress < 140 < 140 MPaMPaBending stressBending stress < 10 < 10 MPaMPa

Load: Weight + Seism

Max stress <130 Max stress <130 MPaMPaBending stress < 20 Bending stress < 20 MPaMPa

Load: Weight + VDE

Gravity support



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Conclusions

• TFC structures design is well advanced.

• Design optimized in order to reduce mass and cost

• Actually detail design tasks are ongoing.

• Future activities (local models, half torus model) are planned.

jt-60 sa toroidal field coil structural analysis

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