A Brief Overview of ILC Quadrupole Concepts

1
A Brief Overview of ILC Quadrupole Concepts
Outline

• Estimate of scope
• A Look at Requirements
• Some of the Critical Issues
• Some Examples of LC Quadrupoles
• Disclaimer information presented here is
  borrowed from Snowmass talks which were in turn
  borrowed from other talks

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An Estimate of Scope

• Use Tesla Design Report as a guide for estimates
  of ILC quantities - but dont take any numbers
  which I present here to be definitive (or even
  close?)
• Design concept has one quadrupole per every 2
  cryomodules for beam focusing
• There are on the order of 2000 cryomodules in the
  main linac (8 cavities/module, 9 cells/cavity)
• There will be on the order of 1000 quadrupoles
• This is clearly an industrial quantity whatever
  the actual or eventual numbers may be
• ILC must run from 200 500 (1000?) GeV?Must be
  upgradeable, adding high gradient cavities

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Scope, cont.

• The quadrupole assemblies will also include weak
  dipole (horizontal and vertical) correctors
• Correct for misalignment
• Correct for curvature of the earth over the
  length of the linac (depends on design choice)
• Not a magnetic component, but with every
  quadrupole there will be an adjacent beam
  position monitor (BPM)
• A proposed alternative layout (Snowmass 2005)
  would have the quadrupole and BPM in a separate
  cryomodule (aka cryostat) between cavity modules

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A Look at Requirements

• This is not a comprehensive look at requirements
  the requirements are still being developed
  but should be a guide to most obvious, important,
  or difficult ones
• Beam pipe Inner Radius 39mm ? 2?40mm OD
• Defines minimum coil diameter and thus a major
  factor field-gradient characteristics
• Typical figure of merit is the integrated
  strength ?g?dl (T) ( T/m ? m )
• Gradient, g, is nominally 60T/m
• Coil length .6m
• There is an obvious tradeoff between gradient
  (i.e., peak field) and coil length but the
  quadrupole slot length is constrained by
  machine design cavity spacing

Strength 35T
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Requirements, cont.

• Dipole trim coils (from the Tesla TDR)
• Figure of merit is the field integral ?B?dl
  (T-m)
• Typical strength 0.05 T-m
• Alignment (from the Tesla TDR)
• Quadrupole axes to within ?0.2mm of the ideal
  beam
• Quadrupole roll' tolerance of ?0.1mrad
• Operating temperature 2K
• Operating current ? 10s few 100s A
• Inductance vs. HTS leads, heat leak, cost

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Requirements, cont.

• Magnetic field
• Field quality (in terms of a multipole expansion)
• Skew quadrupole lt3?10-4 (normalized to the field
  at the reference radius g?Rref)
• Higher order terms lt1?10-3
• Field in the cavity region must not exceed 10?T
  during operation, lt1?T during cavity cool down,
  to preserve low surface resistance
• Control of stray field from the quadrupoles at
  the cavities will require shielding at the
  quadrupole
• Iron or,
• Passive superconductor

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Some of the Critical Issues

• Alignment
• Need to control alignment vs. excitation current
• Basic design choice cos(2?) vs. iron dominated
• Structural details, coil support, etc.
• With quadrupoles in the middle of the cryomodule
  (baseline), then alignment becomes more
  challenging
• Location in the cryomodule, support, assembly,
  access we have to think about this
• Cold test of cryomodules? More to be learned
  here
• If quadrupoles and BPMs are in a separate
  cryostat (alternative), then accurate cold
  measurements could be made on a test stand
• Reference to external fiducials directly
  accessible
• Testing is straightforward (e.g., warm-cold
  positions can be measured)

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Critical Issues, cont.

• Stray field at (nearest) cavity lt10?T
• Is it possible to estimate warm (at low current?)
• In situ cold on test stand?
• (In)directly in a cold test with cavity?
• Cavity performance with magnet on, magnet off
  is the empirical stray field test
• In principle, one can measure once to verify
  design and then establish QA procedures to verify
  correct materials and assembly during production
• - Potential persistent current effects in
  superconductor need to understood and accounted
  for in operation (lt1?T when cavities are warm)

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Critical Issues, cont.

• Design choices
• Coil dominated e.g.,cos(2?)
• Field quality determined by conductor placement
• High peak fields, shorter slot length
• Coil shape can change during excitation affecting
  field center
• Iron dominated, aka superferric
• Peak fields limited by iron saturation (?2T)
• Slot length increase for fixed integral strength
• Tradeoff between peak field and slot length
• Operating current number of turns, inductance,
  leads, heat leak
• Overall optimization with quench protection,
  cryogenics, power distribution, etc.

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Some Quadrupole Examples
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Some Quadrupole Examples

• Tesla Design detail

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Quadrupole Examples, cont.

• TESLA type Cold Mass made at CIEMAT (Spain)

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Quadrupole Examples, cont.

• Superferric design being tested for TTF/XFEL
• XFEL Magnet Work is being done by CIEMAT
• About a factor of 2 shorter than TTF design
• Field calculations are still underway
• Check fields outside the magnet
• Remnant fields from trim coils

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Quadrupole Concepts, cont.

• Superferric Design Concept
• Vl. Kashikhin, Fermilab Proton Driver
• Pole tips determine field
• Coils wound in forms then inserted

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Quadrupole Concepts, cont.
Quadrupole design from NSCL MSU for TRASCO (Italy)
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Quadrupole Concepts, cont.

• In general, the quadrupoles are relatively small
  assemblies similar in size to corrector magnet
  assemblies in existing hadron colliders such as
  the Tevatron, the LHC, etc.
• The field quality requirements are not
  particularly stringent by collider standards
• Designs should not push superconductor limits
• Approaches could vary from Rutherford style cable
  cos(2?) to single strand, random wound
  superferric designs
• However, there are some details of concern
• Alignment
• Stability of field center with excitation current
• Stray field at cavities
• And, cost and reliability are always issues!

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References

• Some references
• Tesla Technical Design Report
• http//tesla.desy.de/new_pages/TDR_CD/
• Snowmass 2005
• http//alcpg2005.colorado.edu8080/alcpg2005/progr
  am/accelerator/WG2/chris_adolphsen20050817160632.p
  df
• http//alcpg2005.colorado.edu8080/alcpg2005/progr
  am/accelerator/WG2/lutz_lilje20050830174949.ppt
• http//alcpg2005.colorado.edu8080/alcpg2005/progr
  am/accelerator/WG2/carlo_pagani20050821231559.pdf
• and more
• MSU NSCL quadrupole
• http//ieeexplore.ieee.org/iel5/77/21913/01018412.
  pdf