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Abstract. Magnetic Specifications and Tolerances Weiming Guo, NSLS-II Project

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Magnetic Specifications and Tolerances

Weiming Guo, NSLS-II Project

In this presentation I briefly introduced the physics considerations that lead to the current cell configuration, the number, type and separation of the magnets in the lattice, and the specifications on the magnet tuning range and field quality. The statistical results were then shown for the received magnets. By examining the strength uniformness, magnet saturation, and the harmonic values, we conclude that the magnets are of good quality and meet our requirements. A comparison with SOLEIL magnets was made and we found the lower order harmonic terms of NSLS-II magnets are much smaller, which will improve the accelerator performance.

*Work performed under auspices of the United States Department of Energy, under contract DE-AC02-98CH10886

requirements and specifications

Requirements and Specifications

Weiming Guo


BNL, April, 2012

  • Physics considerations leading to the magnet specifications
  • Overview of the quality of the received NSLS-II magnets
  • Comparison with SOLEIL magnets
  • Retrospect and remarks
specifications concerning magnets
Specifications Concerning Magnets
  • Type and number of magnets, aperture, magnetic separation
  • Quadrupoles and sextupoles: strength, tuning range, stability, and field quality
  • Dipole: strength, homogeneity, and stability
  • Current, voltage
deterministic or nondeterministic
Deterministic or Nondeterministic
  • Some basic parameters determined early by administrative decision:
  • Magnet aperture, number and strength of the dipoles
  • Parameters determined through optimization (Deterministic)
  • Number and type of multipole magnets, polarity, and power connection pattern
  • Magnet strength and tuning range
  • Sextupole uniformity
  • Parameters determined through interaction with engineering groups (interactive and iterative):
  • Power supply tolerances: Physics requirements ←→ mitigation approaches
  • ←→ commercial availability
  • Field quality (harmonics): general guidelines from physics ←→ Initiated from magnet design
  • and prototyping ←→ approved by beam dynamics ←→ adjustments based on fabrication
  • feedback
  • Alignment tolerance ←→ field quality, implementation approaches
  • Magnet measurement quality must be sufficient to check physics requirements on field,
  • however limited by cost and schedule

Cell Configuration and Evolution










3-pole wiggler

  • 10 quadrupole magnets per cell, independent power supplies (initially 4 quads in the matching section)
  • 9 sextupole families, 3 chromatic and 6 geometric. (initially 12 sextupole families)
  • 2 slow correctors and 2 BPMs per girder to allow girder by girder orbit correction
  • 2 additional high stability BPMs in each straight section to improve stability
  • 3 fast correctors per cell for fast orbit correction
  • most of the magnet to magnet separation is standardized to 17.5 cm.
  • (straights increased from 5/8 to 6.6/9.3)
  • 3-pole wiggler was added to the lattice to provide dipole radiation


magnet tuning range
Magnet Tuning Range
  • Sextupole strength limit: (400 T/m2)
  • It is 30% more than the typical settings for chromaticity correction for chromatic sextupoles
  • Geometric sextupoles have the same limits as the chromatic sextupoles
  • An assemble of lattice solution have been optimized, and dynamic aperture is not limited by the maximum strength

Quadrupole tuning range (K1 1/m2)

  • Methodology to the Quadrupole Magnet Tuning Range
  • Searched an assemble of solutions with working point evenly distributed in the tune window (νx±1, νy±1);
  • Lattices with smaller beta functions in the straights; and
  • low momentum compaction lattice
  • The table is the statistical results of all the above lattice solutions.

Quad Multipole Specification (r=25mm)

Sext Multipole Specification (r=25mm)

Higher Order Multipole Specification

Amplitude-tune dependence At δ=-2.5%

  • The higher order multipoles generates nonlinear detuning, which limits the dynamic aperture.
  • The off-momentum particles are more susceptible due to the large orbit excursion, which is the reason for large aperture at the peak dispersion.
  • The dynamic aperture is acceptable when the multipoles are multiplied by a factor of 2.

Dynamic aperture at δ=-2.5% when the multipoles are multiplied by the indicated factors

sextupole linearity and uniformity
Sextupole Linearity and Uniformity



Sextupole strength uniformity

Required 0.5%rms, measured: <0.3%rms

Sextupole transfer function: linear region

quadrupole linearity and uniformity
Quadrupole Linearity and Uniformity

Quadrupole strength uniformity

At half of the full excitation current

Quadrupole saturation: <5%

quadrupole 1 st systematic harmonic
Quadrupole 1st Systematic Harmonic
  • B6 started to grow when magnet saturates;
  • However the growth is small and the field quality is in-spec.
typical lower order terms
Typical Lower Order Terms
  • Lower order terms have apparent current dependence
  • Small current: pole move?
  • Large current: saturation.
typical higher order terms
Typical Higher Order Terms
  • Higher order terms: small, in-spec, and current-independent.
summary on magnet field quality
Summary on Magnet Field Quality
  • Uniformity: <0.3% rms for quadrupole and sextupoles, meets requirement (0.5%)
  • Saturation: sextupole linear, quadrupole <5% saturation, field quality meets spec.
  • Lower order harmonics have a small current dependence, and higher order terms
  • are current-independent.
  • Due to assembly errors, a fraction of sextupoles have lower order terms slightly
  • exceeding the specifications , for example, octupole and decapole terms.
  • The higher order terms are mostly small and in-spec.
  • Conclusion: the magnet field quality is very good.
comparison with soleil
Comparison with SOLEIL

Sextupole (Prd and Mesrd SIGMAPHI)

Quadrupole (Prd Danfysik, Mesrd SOLEIL)

retrospect and remarks
Retrospect and Remarks
  • Which terms are important?
  • Answer: lower order terms, a4,b4,a5,b5,a6,b6.
  • Smaller values will definitely improve the accelerator performance.
  • What is the required approach?
  • 1) 1~2x10-4 leads to ~10 μm pole precision, which requires EDM process and
  • 2) Individual shimming to eliminate the assembly errors.
  • Should the quadrupole systematic terms be tighter?
  • Answer: Yes, even though the current specs satisfy our requirement.
  • Should we have specified the whole tuning range rather than a single point?
  • Answer: yes. Meeting the spec at 100% strength is still questionable.
  • Could the magnet types be reduced?
  • Answer: 9801 quad could be replaced by 9809 quad at the price of 1.5m space totally.
  • Should have set tolerances for all specified quantities.
  • Skew quadrupole magnetic length and field quality were not specified in the beginning
  • Reproducibility requirement was not specified on the field quality