Mechanical Analysis of Dipole with Partial

Keystone Cable for the SIS300

A finite element analysis has been performed to optimize the stresses in the dipole of SIS-300. For this the behavior of the

structure during assembly, cool down, magnet operation and the characteristics of the main components are calculated.

Introduction

Distribution of ponderomotive forces in the coil cross-section (there are an azimuth and radial components)

Conceptual Design Collared Coil

Designs with Yoke Support .

We consider Collared Coil. The stainless steel collars have 3 mm thick (aluminum collar is not considered because of large AC losses).

•Differences of displacements between vertical and horizontal outer radii of the collars. Red line is marked permissible differences δR after excitation.

Self-Supported Collared Coils

The difference of radial displacements between

vertical and horizontal outer radii of the collars of the collars should not exceed 0.05 mm (requirements to

field quality)

Collar wide, mm

The dipole mechanical structure with Yoke Support

Yoke has a vertical split, at which magnetic lines go along gap and do not intersect it. A vertically split yoke design has been chosen to provide a reliable support of the collars by the yoke mostly in horizontal direction, where radial forces are the largest.

Finite element models

1 - coil, 2 - inter-turn spacers (wedges), 3 - key, 4 –collars, 5 – yoke, 6- cylinder

Magnet mechanics

• Collaring An oversized coil is compressed in the press and fixed by keys inserted into collars. Coils force the

collar to expand beyond the nominal loose collar dimensions.

• Yoking and Cylindering or Assembling Collared coil is compressed by the yoke and cylinder; collar is forced inward. Cylinder halves are welded together.

• Cooldown The collared coil shrinks and, it can loss or remains contact with the yoke. Cylinder contracts around the stiffer iron and stress in the cylinder is

increased. The yield strength of the cylinder is increased faster than strength in the cylinder.

• Excitation Azimuth ponderomotive forces decrease the coil pre-stress at the pole region; however because of

there is an opposite large pre-stress, coil remains in contact with the pole. The radial ponderomotive forces act at the collar. These forces are transmitted to the yoke and the cylinder.

Material properties

Component Material Elasticity Modulus, GPa

Poisson’s Ratio

Thermal Contraction 10-5, K-1

300 K 4.2 K

Coil (Radial) (Coil with PP

insulation)

12.6 18.9 0.33 1.52

Coil (Azimuth) (Coil with PP

insulation)

11.2 12.6 2.15

Ground Insulation

polyimide 13 13 0.3 2.5

Wedges, collars, key, cylinder

Stainless steel

210 225 0.3 1.027

Yoke Iron 210 225 0.3 0.7

Yoke-collar, Yoke-Yoke, Yoke-cylinder interface

for structure with Yoke Support

Parameters of contact surfaces1. contact surface between collar

and yoke at angle from 0 to 14 degrees (before key)

2. contact surface between collar and yoke at angle from 14 to 45 degrees

3. contact surface between collar and yoke at angle from 45 to 90 degrees

4. contact surface between yoke and cylinder

5. contact surface between half yokes at the bottom of the iron yoke split

6. contact surface between half yokes at the top of the iron yoke split

Design with Yoke Support

Open gap structure Close gap structure

Gap between half yokes is opened after assembling, closed after cooling. The collared coil is kept always in contact with the yoke.

Gap between half yokes is always closed. The collared coil loses contact with the yoke after cooling and has contact at 3 T .

Variant 1 Variant 2

Pre-stress change in the superconducting coil layers

Collar- yoke interference is 0.05 mm, A vertically split yoke with a tapered gap: gap is 2*0.1 mm at the top and 2*0.07 mm at the bottom, Initial prestress in cylinder is about 80 MPa (interference yoke cylinder is 0.14 mm)

Stages were considered : 1. Collaring2. assembling, 3. cooling, 4. excitation (1 T)5. excitation (3 T)6. excitation (6 T)

Variant 1

Stress change in the cylinder

Changes of contact Forces in inner layer during Stages

Change of radial displacements in pole and median of inner layer during Stages

Collar- yoke gap is 0., A vertically split yoke with a tapered gap: gap is 2*0.1 mm at the top and 2*0.07 mm at the bottom, Initial prestress in cylinder is about 80 MPa (interference yoke cylinder is 0.14 mm)

Variant 2

Pre-stress change in the superconducting coil layers

Stress change in the cylinder

The contact Forces in inner layer change during Stages

Changes of radial displacements in pole and median for inner layer during Stages

Conclusion

The study of dipole mechanics showed that it is necessary to have for Close gap structure :

1. yoke - yoke gap: top - 2*0.1mm, bottom - 2*0.07mm

2. Initial prestress in cylinder may be about 80 MPa (interference yoke cylinder is about 0.14 mm) thickness of cylinder is 7 mm

3. Maximal prestress in coil is about 90 MPa.4. Collar- yoke interference either 0.05 mm or 0. ?