Superconducting Magnet Group

Superconducting magnet development for ex-situ NMR

LDRD 2003

Paolo Ferracin, Scott Bartlett

03/31/2003

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Contents

• Introduction• Description of the prototype

– Conductor and cable– Superconducting coil– Coil pack– Mechanical structure

• Magnetic design– Analytical analysis– Coil configuration

• Lorentz forces• Mechanical design

– Stress analysis• Work plan update• Conclusions

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Introduction

• Proof of principle of an ex-situ NMR superconducting magnet– Volume (sweet spot) with

high and homogeneous field in a “free region”

• LDRD proposal prototype design– Three horizontal coils (NbTi)– Field of ~ 2000 Gauss– Sweet spot: 3 mm volume at

15 mm– Homogeneity of 10-3

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Prototype: conductor and cable

• Strands 0.7 mm– Nb3Sn filaments in a copper matrix

• Cable– 20 strands– 8 mm wide and 1.3 mm thick– 0.1 mm insulation (fiberglass)

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Prototype: superconducting coil

• Coil design: subscale magnet program

• Cable is wound around an iron island

• Two layers, 20 turns each

• Coil main dimensions– 300 mm X 110 mm X 15 mm

• Coil confinement: horse shoe

• Heat treatment, epoxy impregnation

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Prototype: coil pack

• Four coils:– SC-11 and SC-12 (under fabrication)– SC-01 and SC-02 (SM baseline)

Sweet spot side Connection side

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Prototype: mechanical structure

• Steel pads

• Iron yoke

• Aluminum shell

• Diameter: 620 mm

• Thickness: 110 mm

• Assembly:– Key and bladder

(new LBNL technology)• Cool-down to 4.3 K

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Magnetic design: analytical analysis

• Analytical study– Line currents– Accelerator magnet formalism:

- I

x

y

+ I

d

t

nr

a

nIrB n

nn coscos

, 10

– Field expressed in a series of harmonics:

B1: dipole; B3: sextupole; B5: decapole

• Goal: maximize the B1 and minimize the higher order harmonics

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Magnetic design: coil configuration

• Optimization with blocks of conductors instead of line currents

• Once fixed the position (and the number) of the blocks, two possible coil configurations:

x

y

d

t

Vertical configurationHorizontal configuration

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Magnetic design: prototype coils

• The vertical configuration was chosen– Less efficient but more

degrees of freedom– More suitable for field quality

optimization

• Main features– 4 subscale magnet coils– Current: 11 kA – Field in the sweet spot: 2600 Gauss – Distance of sweet spot from the structure: 45 mm– Homogeneity: limited by the choice of the

subscale magnet coils (~10-2 in 3 mm volume)

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Lorentz forces

• Horizontal Lorentz forces – tend to separate the coils– FX1 = 600 kN– FX2 = 664 kN

• Vertical Lorentz forces– No vertical support (sweet spot region)– Magnetic design must limit outward forces– In the prototype negligible outward forces

• Pre-stress– To limit the conductor movement (quench) the

coils are pre-compressed by the mechanical structure

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Mechanical design: stress analysis

• The pre-compression is provided by– Bladders and keys: 40 %– Different thermal contraction

between aluminum shell and iron yoke: 60 %

• Final stress in the shell: 200 MPa

• The stress in the shell transferred (via yoke and pad) to the coils

• No vertical support

• Full access to the sweet spot

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Work plan update

• Design: – Basic magnetic/mechanical analysis completed– Design studies of optimized magnets will continue through

September• Drawings:

– ProE model and drawings are being completed• Parts:

– Support structure parts available by end of April• Fabrication:

– New coils already wound; heat treatment and impregnation completed by mid April

– Assembly completed by end of May• Test:

– June-July time frame• Analysis:

– August-September (abstract will be submitted for MT18)

03/31/2003 Superconducting Magnet Group Paolo Ferracin

Conclusions

• The prototype demonstrates the main design features of the ex-situ magnet:– Mechanical structure with full access to saddle

point– Field in the sweet spot– Distance of the sweet spot– Coil configuration– Fabrication and assembly techniques

• Next steps– Field homogeneity – First ex-situ NMR experiment