Interaction Region Design Options

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Interaction Region Design Options for a Super-B
Factory
M. Sullivan for the International Committee for
Future Accelerators ee- Factories
Workshop October 13-16, 2003
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Outline

• General B-factory parameters and constraints
• Present B-factory IRs
• Super B-factory IRs
• Summary

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Some Issues and Constraints

• There is always some local synchrotron radiation
  from bending magnets
• PEP-II generates a large amount of local SR in
  order to make head-on collisions.
• KEKB also generates a lot of SR even though they
  have a large crossing angle because they designed
  for on-axis incoming beams. This shifts all of
  the bending SR to the downstream side and
  consequently increases the power levels of the
  fans striking the nearby vacuum chambers.

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Constraints...

• The Q1 magnet is always going to be shared
• At least one beam is always bent in this magnet
  generating SR bending fans.
• The Q2 magnet must be a septum magnet
• If this magnet is shared by both beams then one
  loses most of the beam separation because it is
  x-focusing.
• Making this magnet a septum magnet forces a
  certain amount of beam separation at the face of
  the Q2 magnet (about 100 mm between beam center
  lines).

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Detector requirements

• Maximum solid angle
• Try to keep all accelerator components far enough
  away from the IP to maximize the detector
  acceptance
• This conflicts with accelerator requirements to
  minimize the spot size by pushing in the final
  focus magnets
• Adequate shielding from local SR
• The collision beam pipe (usually Be) must be
  shielded from locally generated SR and lost beam
  particles at least well enough to avoid swamping
  the detectors.

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More detector requirements

• Minimum amount of material in the detector
  beampipe
• This conflicts with having enough SR shielding
  (usually a thin coating of Au) to keep detector
  occupancy at acceptable levels
• Minimum radius for the beam pipe
• This must be balanced with the requested thinness
  of the beam pipe. The smaller the beam pipe the
  more power it must be able to handle (kW).

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Still more detector requirements

• Large high-field solenoid
• This forces the final shared magnet (Q1) to be
  either permanent magnet or super-conducting
  (maybe also Q2)
• Adequate shielding from beam backgrounds
• Collimators and shield walls are needed to
  protect the detector from backgrounds generated
  around the ring
• Low pressure vacuum system near the IP
• This minimizes lost beam particles generated near
  the IP that can not be collimated out

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Machine Parameters that are Important for the IR
PEP-II KEKB LER energy 3.1 3.5 GeV HER
energy 9.0 8.0 GeV LER current 1.55 1.38 A H
ER current 1.18 1.05 A ? y 12.5
6.5 mm ?x 25 60 cm X emittance 50 20 n
m-rad Estimated sy 5 2.2 mm Bunch
spacing 1.89 2.4 m Number of
bunches 1034 1284 Collision angle head-on ?11 mr
ads Beam pipe radius 2.5 2.0 cm Luminosity 6.6
?1033 10.6?1033 cm-2 sec-1
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Beam Parameters for a PEP-III 1?1036 Luminosity
Accelerator
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PEP-III Super B

• Now Projected Upgrade Super B
• LER energy 3.1 3.1 3.1? 3.5
  GeV
• HER energy 9.0 9.0 9.0? 8.0
  GeV
• LER current 1.8 3.6 4.5
  22.2 A
• HER current 1.0 1.8
  2.0 9.7 A
• y 12.5 8.5 6.5 1.5
  mm
• ?x 28 28 28 15
  cm
• X emittance 50 40 40 70
  nm-rad
• Estimated sy 4.9 3.6
  2.7 1.7 mm
• Bunch spacing 1.89 1.5
  1.26 0.63 m
• Number of bunches 1034 1500
  1700 3400
• Collision angle head-on head-on
  0?3.25 ?12 mrads
• Beam pipe radius 2.5 2.5
  2.5 1.5-2.0? cm
• Luminosity 6.6?1033 1.8?1034
  3.3?1034 1?1036 cm-2 sec-1

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2 cm radius and 1 cm radius beam pipes
The 1 cm radius beam pipe intercepts about 5 kW
of power from the LER and nearly the same amount
of power from the HER
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• Further optimization possibilities
• Lower the amount of upstream SR at the expense of
  increasing the downstream SR (more like KEKB)
• Offset the Q1 magnets as shown in the drawing (B.
  Parkers suggestion)
• ..

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KEKB Upgrade Plans

• Now Upgrades SuperKEKB
• LER energy 3.5 3.5 3.5 GeV
• HER energy 8.0 8.0 8.0 GeV
• LER current 1.38 2.0 9.4 A
• HER current 1.05 1.1 4.1 A
• y 6.0 6.0 3.0 mm
• ?x 58 58 15 cm
• X emittance 20 20 33 nm-rad
• Estimated sy 2.2 2.2 2 mm
• Bunch spacing 2.4 2.4 0.6 m
• Number of bunches 1284 1284 5018
• Collision angle ?11 crab ?15
  (crab) mrads
• Beam pipe radius 2.0 1.5 1-2 cm
• Luminosity 1.06?1034 2-3?1034
  2-6?1035 cm-2 sec-1

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Summary
The Interaction Region of a B-Factory has many
conflicting requirements. The very high beam
currents challenge the IR design in the areas of
backgrounds, HOM power, SR power, The trick is
to achieve a kind of best balance between these
requirements that maximizes the luminosity for a
given B-factory design.