Abstract

BROOKHAVEN SCIENCE ASSOCIATES

Abstract

Magnet Design Workshop: Magnet Design and Analysis

Charles Spataro, NSLS-II Project NSLS-II is a new 3Gev synchrotron light source designed to deliver state-of-the-art emittance with top-off operation for constant output. This presentation documents the magnet design challenges and choices as well as methodology and studies undertaken during the magnet design phase. Also described are a number of the problems encountered and solved from prototyping to full production of the almost one thousand magnets that comprise the storage ring. *Work performed under auspices of the United States Department of Energy, under contract DE-AC02-98CH10886


Charles Spataro

Magnet WorkshopMagnet Design/Analysis

2NSLS-II Magnet Workshop, April 11-12, 2012


Magnet Design/AnalysisOutline

• Magnet Design Choices/Challenges• Magnet Studies/Chamfering• Problems Encountered and Solved.

Quadrupole

Fast CorrectorDC Corrector

ID Corrector

Sextupole

Dipole3NSLS-II Magnet Workshop, April 11-12, 2012

3


Magnet Design Challenges

The GoalTo design a magnet that can be built with current techniques, meets the harmonic specification, is reliable and reproducible, be manufactured for a low cost and fast as possible with minimal running costs and maintenance.



Design Considerations

NSLS-II Magnet Workshop, April 11-12, 20125

Power

Vacuum chamber

Beam optics

Cooling

Manufacturability

Field quality

Physical space

Capital costs

Running Costs

Survey

Magnet Design

First Article or Prototype

5


Magnet Design Challenges

What can be designed is different then what can be built-especially pole shape.

Space limitations and tight harmonic specifications is what drove the need for very tight machining and assembly tolerances on the order of 10-20 microns.



Magnet Design -Choices• Harmonic Specification

• Build to print vs harmonic specification

• Steel quality

• Physical size/Aperture size

• Ratio Good field radius/aperture radius

• Machining methods

• Magnet type-single vs combined function

• Magnet shape dipole- curved or straight

• Magnet type- C vs H

• Assembly choice- 2, 4, 6 lamination construction

• Power supply limits

• Mechanical constraints

• 2D/3D Design Software

• Material choices



Building to Harmonic Specification

Pros:• Allows innovative design from various manufacturers to be

incorporated in final design.• Do not have to accept magnets that do not meet harmonic

spec resulting in a better performing machine.

Cons:• Manufacturers need ability to measure harmonics• Differences between manufacturer and BNL

measurements.• More BNL design involvement from first article through

production



Assembly Choice 2 Piece vs 4 Piece Lamination

Smaller assembly errors

Easier to align

Harder for coil installation

Limited shimming

Larger assembly errors

Harder to align

Easier coil installation

Shim broader range of harmonics

2 Piece lamination 4 Piece lamination



Magnet Design Software

• Software choices dependent on cost, desired accuracy, and calculation time.

• 2D vs 3D Calculations.• Finite Element vs Finite difference analysis. Examples:

Tosca, Poisson,Mermaid, Radia, Roxie.• Expensive software does not necessarily generate the

best solution.• User knowledge and experience is key.

Radia Mermaid Opera Poisson Roxie



Magnet Design Choices:Linear vs Non-Linear Analysis

Non-Linear modeling:• Accurate modeling of magnetic models.• Long meshing time and long solve time.

Linear modeling:• Inaccurate modeling of fields, saturation,etc.• Short solve time.• May be suitable in some cases for first pass/quesstimate.

Key to robust, accurate design

Should include key design concerns such as:

Linear vs non-linear analysis, Packing factor, saturation,mesh size, material choices



Linear vs Non-Linear Analysis

• Linear analysis can lead to huge problems later on (saturation, incorrect fields, etc.)

• Non-Linear analysis helped determine that some quad magnets were undersized-additional iron thickness and length were added to create a more robust design.

You can never have too much iron!



66 mm Quadrupole – Linear Materials

No saturation at poles and a field of 18.2 T !!



66 mm Quadrupole – Non-Linear Materials

Saturation at pole tip edges and a field of only 3.3T14NSLS-II Magnet Workshop, April 11-12, 2012

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Magnet Manufacturer Program Support

Conclusion: BNL magnet design support critical to success of magnet production



Multipole Harmonic Specification-Choices Made

• Single function magnets (ie, no corrections coils).• Magnets were built to Harmonic Specification.• Aperture and good field region radius determined by ring location.• R= 25mm for 66mm Quad and 68 mm sextupole. Low dispersion region.• R=30mm for 90mm quadrupole and 76 mm sextupole high dispersion

region.• Two-piece lamination was chosen.• 1006 steel was specified.



Magnet Chamfering/Shimming

Sextupole-Shimming of center poles used to control b1 and b5 harmonic

Quadrupole- Shimming of side blocks used to control b3,b4

Shim

Shim

Shim



Fine Tuning of Harmonics Through Chamfering

Pole Chamfers

Tip Chamfer

There are two different types of chamfers: Pole and Tip for control of b6 in the quadrupole and and b9 in the sextupole.


• Tip chamfer Increases b6 in the quadrupole or b9 in the sextupole.

• Pole chamfer- Decreases b6 in the quadrupole or b9 in the sextupole


Dipole Matching Chamfering Method

A straight chamfer across the edge of the nose is used to tune the sextupole term.

An angled chamfer across the edge of the nose is used to tune the quadrupole term.



Perturbation Study:Machining and Assembly Errors


68 mm Sextupole 2D Perturbation Study


35 mm Dipole StudiesNose & 50mm Solid Plate & 1mm Short Shim


Dipole Studies


Dipole StudiesBest Option:75mm Solid Block + < 1mm Shim

Solution: Leave the dipole nose as is

Best Option


Sextupole Chamfer: b9 Experimental vs Calculated


Magnet Problems Encountered and Solved:Limited Axial Space

Problem: ID Corrector with a 45 mm yoke length and 84mm overall length with only 90 mm of space available in lattice.

Initial design used water cooled coils but current was too high and voltage too low.

Solution: Use smaller conductor to increase coil length and use chill plates instead of water-cooled conductor.

90 mm


Chill plates


Magnet Problems Encountered and Solved:66mm Quadrupole Saturation

Problem: Saturation led to a large variation of the b6 harmonic with current.


Quad Lengthening Study


Magnet Problems Encountered and Solved 66mm Quadrupole Saturation

Problem: Saturation led to a large variation of the b6 harmonic with current.

Solution: Increased yoke length and backleg thickness created a more robust design. In one case, the baseplate was dug out so the backleg could be increased.



Magnet Problems Encountered and Solved: a3 Current Dependency

Problem: a3 harmonic in the quadrupoles became current dependent due to a top-down asymmetry.

Solution: Stainless steel or aluminum shim 3 mm thick was installed between baseplate and yoke.

Shim



Magnet Problems Encountered and Solved: a3 Current Dependency


Magnet Problems Encountered and Solvedb6 Too large after tip Chamfering

• Problem: The tip chamfer on a quadrupole was machined incorrectly for a number of yokes which pushed the b6 harmonic out of specification.

• Solution: A 1.5 mm pole chamfer was added to the existing radial chamfer to drive b6 well into specification.

Pole chamfer



Magnet Problems Encountered and Solved:Variation in 35mm Dipole Field

• Problem: A large periodic variation was found in the dipole field.

Solution: Modeling led to the conclusion that it was caused by the gap between the top yoke plate and laminations and the bolt holes at 250 mm intervals in the top plate. The variation was deemed ok by the Physics group.

Holes in top Plate



Problem: Higher fields in dipole laminations.

Solution: Top, bottom and back plates changed from mild steel to 1006 steel to redistribute flux.

Magnet Problems Encountered and SolvedToo High fields in 35 mm Dipole Yoke

Very little flux in the mild steel plate Note flux in 1006 plate

Mild Steel Plates 1006 Plates



Conclusion

Magnet design support is not finished until all magnet manufacturing issues are resolved. And it still continues to this day...

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