IR Issues in e e

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IR Issues in ee- Circular Colliders
M. Sullivan
Snowmass, 2001
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Outline

• Ground Rules
• Issues
• Design Comparisons
• Summary

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Ground Rules

• Two ring machines (even CESR)
• Small bunch spacing
• High currents (gt1A)

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Issues

• Getting the beams into and out of collision
• Shared beam pipe
• HOM heating
• Shared magnetic elements
• Beam steering in FF quads
• Synchrotron radiation fans

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More issues

• Synchrotron radiation from FF quads (Stan H.
  slide)
• Flat beams are much easier than round beams
• Low emittance beams are easier than high
  emittance beams
• Beam tail distributions

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Synchrotron Radiation Fans with 240 mrad x 1000
mrad Collimation
NLC beams
courtesy of S. Hertzbach
8.5s x 28 mrad
25s x 40 mrad
Very low emittance beams
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Still more issues

• SR masks generate local impedence
• More HOM power
• Detector field
• Orbit compensation
• Coupling correction
• Radiation damage to detector components

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Even more issues

• Motion of FF quads
• Monitor and/or feedback correction
• Stress fatigue from thermal cycling
• Storage ring issue when beams are lost
• Linear collider issue ??? (rep rate or beam
  trips)

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Head-on Symmetric PM elements HOM SR fans
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Crossing angle Incoming beams on axis SC
quads Compensating solenoids HOM Outgoing SR fans
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Crossing angle SC quads Compensating
solenoids HOM?
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Summary
There are a lot of things to keep track of
when designing an IR. As beam currents increase,
spot sizes decrease, and beam energies increase
it will become harder to reach decent compromises
between detector backgrounds, HOM power, magnetic
field strengths, etc. On the other hand, if this
was easy it would have been done already and we
would have to look for something else to keep us
off the streets.