# Presentation: 427526

## Shell-based Support Structures for Nb3Sn Accelerator Quadrupole Magnets

- Paolo Ferracin

- Workshop on Accelerator Magnet, Superconductor, Design and Optimization
- CERN
- May 19 – 23, 2008

## Outline

- Introduction: shell based support structures
- Principles of operation
- Overview of LARP shell-base structures
- Assembly, cool-down effect and excitation
- Axial support
- Length scale-up
- Shell axial strain
- Flexural rigidity and LHe containment
- Alignment
- Conclusions

- Paolo Ferracin

- 05/23/08

## IntroductionShell based support structure

- Shell-based structures
- Aluminum segmented shell (solid tube)
- 4-piece yoke with open gaps  during operation
- Assembly through two sub-assemblies
- Pre-loading with water pressurized bladders
- Maximum stress reached after cool-down
- Axial coil support by end-plate and axial rods
- The concept has been adopted to cope with the requirements of high field (high forces) Nb3Sn (brittle conductor) magnets
- Capability of providing large forces
- Precise control of coil pre-load
- Through LARP Magnet R&D  accelerator quality features

- Paolo Ferracin

- 05/23/08

## Principles of operation Bladder pressurization

**Deform. shape with**
**displ. scaling = 20 **

- Paolo Ferracin

- 05/23/08

## Principles of operation Key insertion and bladder deflation 

**Deform. shape with**
**displ. scaling = 20 **

- Paolo Ferracin

- 05/23/08

## Principles of operation Cool-down 

**Deform. shape with**
**displ. scaling = 20 **

- Paolo Ferracin

- 05/23/08

## Principles of operation Excitation

**Deform. shape with**
**displ. scaling = 20 **

- Paolo Ferracin

- 05/23/08

## Overview of LARP shell-base structuresSubscale quadrupole (SQ)

- 2005: first racetrack quad. in a shell-based structure
- 0.3 m long
- Bore-coil aperture: 110-130  mm
- Imax (SQ02b, 1.9 K) = 98% Iss
- Bpeax_max: 11.8 T
- Gmax: 89 T/m
- Structure components aligned

- Coils: LBNL
- Structure: LBNL
- Test: LBNL, FNAL

- Paolo Ferracin

- 05/23/08

## Overview of LARP shell-base structuresTechnology quadrupole (TQS)

- 2006: First cos-theta quad. in a shell-based structure
- 1 m long
- Bore-coil aperture: 90 mm
- Imax (TQS02a, 4.5 K) = 90% Iss
- Bpeax_max:  11.2 T
- Gmax:  220 T/m
- No alignment

- Coils: FNAL, LBNL
- Structure: LBNL
- Test: LBNL, FNAL

- Paolo Ferracin

- 05/23/08

## Overview of LARP shell-base structuresLong Racetrack (LRS)

- 2007: first long racetrack dipole in a shell-based structure
- Common-coil configuration
- 3.6 m long
- Imax (LRS02, 4.5 K) = 96% Iss
- Bpeax_max:  11.5 T
- No alignment

- Coils: BNL
- Structure: LBNL
- Test: BNL

- Paolo Ferracin

- 05/23/08

## Overview of LARP shell-base structuresLong Quadrupole (LQS)

- 2008 (under construction): first long cos-theta quad. in a shell-based structure
- 3.6 m long
- Iss (4.5 K) = 13.8 kA
- Bpeax_ss:  12.3 T
- Gss:   240 T/m
- Structure components aligned

- Coils: FNAL, BNL
- Structure: LBNL
- Test: FNAL

- Paolo Ferracin

- 05/23/08

## Overview of LARP shell-base structuresHigh Field Quadrupole (HQ)

- 2008-2010 (under development)
- High coil field and forces
- From 11-12 T to 15 T
- Include accelerator quality features required for the LHC luminosity upgrade
- Large aperture
- Alignment and field quality
- Cooling channels and LHe containment
- First 1 m long model test planned for September 2009

- Paolo Ferracin

- 05/23/08

## Assembly (I)

- Coil-pad sub-assembly
- Pads bolted around the coil
- Bolts “disappear” under compression
- Yoke-shell sub-assembly
- Gap keys keep yoke stacks apart and pre-tension the shell

- Paolo Ferracin

- 05/23/08

## Assembly (II)

- Assembly of 4 single shell-yoke sub-assemblies
- Connection of shell-yoke sub-assemblies with tie rods
- Insertion of coil-pad sub-assembly

- Paolo Ferracin

- 05/23/08

## Cool-down effect and excitation

- All the force transferred to the coil (yoke gaps open)
- Increase of shell stress shell  shell - yoke (offset)
- With coil under compression, during excitations to Fnom
- 10 MPa increase of shell tension
- With coil – pole separation: increase of shell tension

- Paolo Ferracin

- 05/23/08

## Axial support

- Same approach as in the straight section
- Pre-load aimed at minimizing coil – pole separation in the end (based on computations)
- Four aluminum (or stainless steel) axial rods connected to an end plate
- Increase of rod tension during cool-down
- Pre-load obtained with piston and additional plate

**With axial support**
**Displ. scaling: 50**

**Without axial support**
**Displ. scaling: 50**

- Paolo Ferracin

- 05/23/08

## Length scale-upShell axial tension in LRS01 and LRS02

- LRS01
- High meas. axial strain meas.
- Effect on azimuthal stress

- LRS02 (with segmented shell)
- Reduced axial strain

**LRS**

**LQS**

- LRS01

- LRS02

- Paolo Ferracin

- 05/23/08

## Length scale-up Flexural rigidity and LHe containment

- Assumption: yoke laminations behave like a solid block
- Tie rods compress yoke
- No tensile stresses over the range of deformations
- Max. deflection* ****max* = 0.251 mm
- Required 19.1 mm rod tension
- 400 MPa at 293 K
- External 5 mm thick ss shell
- Additional rigity
- LHe containment

- Paolo Ferracin

- 05/23/08

## Alignment of support structure (LQS)

- Pins to align shell and yoke
- Masters
- Interference key for horizontal alignment
- Mid-plane key for vertical alignment
- During bladder operation masters expand and align (through tilted sides) pads and yokes
- No alignment coil - pad

- Paolo Ferracin

- 05/23/08

## Coil alignment (HQ) (see H. Felice’s talk)

- Aluminum bolted collars on pole keys
- Keys compressed by the collars during all phases
- Part of the shell force intercepted by the collar/ring

- Paolo Ferracin

- 05/23/08

## Conclusions

- Shell-based structures have been proven to provide
- Accurate control and safe assembly pre-load level
- Reduce risks of degrading brittle Nb3Sn superconductor
- Large pre-load force
- Capability of supporting coils in very high field
- Accelerator quality features are being introduced in the structure design through the LARP Program
- Assembly and load of cos-theta coils: TQ
- Alignment of the support structure: SQ, LQS
- Assembly, load, rigidity of long magnets: LRS, LQS
- High field and coil alignment : HQ

- Paolo Ferracin

- 05/23/08

## Appendix

- Paolo Ferracin

- 05/23/08

## Room temperature pre-load Bladders pressurization

- Insertion and inflation of bladders
- Yoke pushed towards shell
- Pad pushed towards coil
- Pad – yoke gap (interference) open mostly on the yoke side

**Displ. scaling: 20 **

**Deform. shape with**
**displ. scaling = 20 **

- Paolo Ferracin

- 05/23/08

## Room temperature pre-load Key insertion

- Shim inserted between key and pad
- Clearance (~0.05 mm) required to insert shim
- Bladder deflated => change of coil stress distribution

- Choice of total interference – bladder pressure based on
- Spring back after bladder deflation
- Required pre-load to reach target coil stress at 4.5 K

**Deform. shape with**
**displ. scaling = 20 **

- Paolo Ferracin

- 05/23/08

## Cool-down effect

- All the force transferred to the coil (yoke gaps open)
- Increase of shell stress shell  shell - yoke
- Indipendent on the starting point (offset)
- Total force on the coil  shell thickness

- Paolo Ferracin

- 05/23/08