Transcript Case Study 4b

11T Dipole for the LHC Collimation upgrade
A Case Study
Chris Segal
Agnieszka Priebe
Giovanni Terenziani
Herve Dzitko
Michele Bertucci
05/02/13
Wire Parameters and Cabling
1.42mm
Cu stabilizer matrix with Cu/non-Cu ratio of 1.5
Strand diameter of 0.8 mm with filament diameter of 25 um
15.8 mm
Strand Diameter = 0.8 mm
strand diameter
Cu/SC ratio
Pitch Angle
Cable Width
Cable Thickness
Insulation Thickness
Filling Factor K
0.8 mm
1.5
16.03 deg
15.8 mm
1.42 mm
0.15 mm
0.33
Superconducting area (SC)
copper area (Cu)
7
6
5
4
3
2
1
1.5 : 1.0
Load Line and Short Sample Conditions
Jsc_ss
2,050 A/mm2
Jo_ss
677 A/mm2
Iss
17,838 A
Bpeak_ss 14.37 T
Jsc_op
Iop
Jo_op
B_peak_op
1640 A/mm2
14,300 A
541 A/mm^2
11.5 T
5000
4500
Critical current density Jc (A/mm2)
4000
3500
3000
Nb3Sn, 1.9 K
Load Line
Nb3Sn 7 K
2500
2050
2000
1500
1640
1000
500
0
5
6
7
8
9
10
Bpeak_op = 11.5 T
11
12
13
Field (T)
14
15
16
17
18
19
20
Bpeak_ss = 14.37 T  100% field in the coil
Coil Layout
The 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 one
Either layout removes the sextuple and decapole contribution
Inner layer needs more wedges since its closer to aperture
sin( 3 3 )  sin( 3 2 )  sin( 31 )  0

sin( 5 3 )  sin( 5 2 )  sin( 51 )  0
α3
α1
α2
EM Forces, stress
Fx  
2 0 J 02
Fy  

20 J 02


3  2  3 3
3 a2 3 4  3 3 
a2 
ln
a1 
a1  a2 a12 

2  36
12 a1
36
6

3  1 3 1 a1 3 1 3 
 a2  ln a1  a1 
2 12
4 a2
12 
  _ mid  plane 
 /3
 f rd  
0
20 J 02

3 
r 3  a13 
r a2  r  
4 
3r 2 
Fx = 2.53 MN/m
Fy = -2.25 MN/m
σ = -265 MPa
Dimension iron yoke, collar, shrinking
cylinder
iron yolk dimensions
shrinking cylinder (support reaches 90% Iss)
collar
Dipole
Section
172.43 mm
6.32 mm
40 mm
Limitation in Magnetic support
structure design
• Iron can’t take more than 2T (Bsat)
r  B  t  Bsat
• Thickness of iron yoke = 21cm
• Magnetic pressure on iron yoke
PM  B
2
2 * 0
 200 MPa
Compare Short sample, operational
conditions, and margins with NbTi
“Every [superconductor] is a [great superconductor]. But if you judge [NbTi] by
“Everybody is a genius. But if you judge a fish by its ability to climb a
its ability to [upgrade the LHC for high luminosity], it will live its whole life
tree, it will live its whole life believing that it is stupid.”
believing that it is [a poor superconductor].”
-Einstein
20
Central field (T)
Nb3Sn 1.9 K
15
Nb-Ti 1.9 K
11T (NbTi saturation)
10
r=28 mm
5
r = 50 mm
r = 75 mm
0
0
10
20
30
Coil width (mm)
40
50
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
• Stable plateau but small degradation
• Less damage for the
Sc parts.
•Optimal training
•Unloading but still
good quench
performance
Support Structure
Collar-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.
Support Structure: Collar-based vs Shellbased
Yoke
Skin
Stress Relief Slot
in inner pole
Shell
Bladder
Pad
Preload
Shim
Yoke
Gap
Yoke
Control
Spacer
Advantages:
• Proven coil positioning
• Proven length scale-up
R&D issues:
• Deliver required pre-stress
• Max. stress at assembly
Collaring
Key
Collar
Axial rod
Key
Coil
Filler
Advantages:
• Can deliver very high pre-stress
• Large pre-stress increase at cool-down
• Easily adjustable
R&D issues:
• Coil alignment accuracy
• Length scale-up
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!