brookhaven science associates abstract magnet design workshop: magnet design and analysis charles...
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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
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Charles Spataro
Magnet WorkshopMagnet Design/Analysis
2NSLS-II Magnet Workshop, April 11-12, 2012
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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
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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.
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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
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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.
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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
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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
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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
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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
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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
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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!
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66 mm Quadrupole – Linear Materials
No saturation at poles and a field of 18.2 T !!
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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
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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.
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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
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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.
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• Tip chamfer Increases b6 in the quadrupole or b9 in the sextupole.
• Pole chamfer- Decreases b6 in the quadrupole or b9 in the sextupole
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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.
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Dipole StudiesBest Option:75mm Solid Block + < 1mm Shim
Solution: Leave the dipole nose as is
Best Option
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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
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Chill plates
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Magnet Problems Encountered and Solved:66mm Quadrupole Saturation
Problem: Saturation led to a large variation of the b6 harmonic with current.
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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.
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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
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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
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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
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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
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