11T Dipole for the LHC Collimation upgrade

A Case Study

05/02/13

Chris Segal Agnieszka PriebeGiovanni TerenzianiHerve DzitkoMichele Bertucci

Wire Parameters and CablingCu stabilizer matrix with Cu/non-Cu ratio of 1.5Strand diameter of 0.8 mm with filament diameter of 25 um

Strand Diameter = 0.8 mm

15.8 mm1.

42m

m

strand diameter 0.8 mmCu/SC ratio 1.5Pitch Angle 16.03 degCable Width 15.8 mmCable Thickness 1.42 mmInsulation Thickness 0.15 mmFilling Factor K 0.33

12

3

56

4

7

Superconducting area (SC)

copper area (Cu)

1.5 : 1.0

Load Line and Short Sample Conditions

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Nb3Sn, 1.9 KLoad LineNb3Sn 7 K

Field (T)

Criti

cal c

urre

nt d

ensit

y Jc

(A/m

m2)

1640

Jsc_ss 2,050 A/mm2

Jo_ss 677 A/mm2

Iss 17,838 ABpeak_ss 14.37 T

Bpeak_ss = 14.37 T 100% field in the coil

2050

Bpeak_op = 11.5 T

Jsc_op 1640 A/mm2Iop 14,300 AJo_op 541 A/mm^2B_peak_op 11.5 T

Coil LayoutThe angles needed to cancel B3 and B5 are (48°,60°,72°) or (36°,44°,64°)

There is a system of two equations, but with three unknowns, there is a degree of freedom allowing for a set of solutions rather than only oneEither layout removes the sextuple and decapole contributionInner layer needs more wedges since its closer to aperture

0)5sin()5sin()5sin(0)3sin()3sin()3sin(

123

123

α1

α3α2

EM Forces, stress

2

31

3

2

200

3/

0_ 34

32rarrarJrdfplanemid

2

1231

31

1

232

200

63634ln

123

3632

232

aaaaaa

aJ

Fx

3

131

2

132

200

121ln

41

121

232 aa

aaaJFy

Fx = 2.53 MN/mFy = -2.25 MN/m

σ = -265 MPa

Dimension iron yoke, collar, shrinking cylinder

iron yolk dimensions 172.43mmshrinking cylinder (support reaches 90% Iss) 6.32mmcollar 40mm

Dipole Section

Limitation in Magnetic support structure design

• Iron can’t take more than 2T (Bsat)

• Thickness of iron yoke = 21cm

• Magnetic pressure on iron yoke

MPaBPM 200*2 0

2

satBtBr

Compare Short sample, operational conditions, and margins with NbTi

0

5

10

15

20

0 10 20 30 40 50

Cen

tral f

ield

(T)

Coil width (mm)

r=28 mmr = 50 mmr = 75 mm

Nb3Sn 1.9 K

Nb-Ti 1.9 K

“Every [superconductor] is a [great superconductor]. But if you judge [NbTi] by its ability to [upgrade the LHC for high luminosity], it will live its whole life believing that it is [a poor superconductor].”

-Einstein

11T (NbTi saturation)

“Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”

Cos(θ) vs Block

• J ~ Cos(θ)

• Self supporting structure

• Circular opening, compact coil

• Easy winding, has long history of use

• Block cable is not keystoned, perpendicular to the mid plane

• Additional internal structure needed

• Ratio central field/current density is 12% lower less effective than cosθ

• Bss is around 5% lower than by cosθ

High Pre-Stress vs Low Pre-Stress

• Less damage for the Sc parts.

•Optimal training

•Unloading but still good quench performance

• Stable plateau but small degradation

Support StructureCollar-based vs Shell-based

• Low field: shrinking outer shell• High field: collars + outer shell• Very high field: bladders, intermediate coil

supports.• If a magnet training does not improve from

4.2 to 1.9K, there is a mechanical limitation.

Advantages:• Proven coil positioning• Proven length scale-upR&D issues:• Deliver required pre-stress • Max. stress at assembly

Advantages:• Can deliver very high pre-stress• Large pre-stress increase at cool-down• Easily adjustableR&D issues:• Coil alignment accuracy• Length scale-up

Support Structure: Collar-based vs Shell-based

CoilAxial rod

ShellBladder

Key

YokePad

Filler

YokeGap

PreloadShim

ControlSpacer

Skin

Collar

YokeCollaringKey

Stress Relief Slotin inner pole

Courtesy of Peter Lee, Florida State University

Courtesy of Peter Lee, Florida State University

References

CERN Accelerator School on Superconductivity lectures (2013):

• Ezio Todesco, "Magnetic Design of SC Magnets"• Pierluigi Bruzzone, "Superconducting Cables"• Fernando Toral, "Mechanical Design of SC Magnets"

Thanks for listening!