1. Interaction Region Design Options e+e- Factories Workshop
for a
Super-B Factory
M. Sullivan
for the
International Committee for Future Accelerators
e+e- Factories Workshop
October 13-16, 2003 1

2. Outline General B-factory parameters and constraints
Present B-factory IRs
Super B-factory IRs
Summary 2

3. 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. 3

4. 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). 4

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7. 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. 7

8. 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). 8

9. 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 9

10. Machine Parameters that are Important for the IR
PEP-II KEKB
LER energy GeV
HER energy GeV
LER current A
HER current A
 y* mm
x* cm
X emittance nm-rad
Estimated sy* mm
Bunch spacing m
Number of bunches
Collision angle head-on 11 mrads
Beam pipe radius cm
Luminosity 6.6 1033 cm-2 sec-1 10

11. Beam Parameters for a PEP-III 11036 Luminosity Accelerator11

12. PEP-III Super B Now Projected Upgrade Super B
LER energy ? GeV
HER energy ? GeV
LER current A
HER current A
y* mm
x* cm
X emittance nm-rad
Estimated sy* mm
Bunch spacing ~ m
Number of bunches
Collision angle head-on head-on 03.25  mrads
Beam pipe radius ? cm
Luminosity     cm-2 sec-1 12

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19. 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 19

20. 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. Parker’s suggestion)
….. 20

21. KEKB Upgrade Plans Now Upgrades SuperKEKB LER energy 3.5 3.5 3.5 GeV
HER energy GeV
LER current A
HER current A
y* mm
x* cm
X emittance nm-rad
Estimated sy* mm
Bunch spacing m
Number of bunches
Collision angle  crab 15 (crab) mrads
Beam pipe radius cm
Luminosity   1035 cm-2 sec-1 21

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23. 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. 23