Interaction Region Design for a Super-B Factory

1. Interaction Region Design for a Super-B Factory M. Sullivan for the Super-B Factory Workshop Hawaii January 19-22, 2004

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

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 downstream fans striking the nearby vacuum chambers.

4. Constraints... • The Q1 magnet is always going to be shared • The Q1 magnet is the closest quadrupole to the IP. At least one beam is always bent in this vertically focusing magnet. This bending generates SR fans. • The Q2 magnet must be a septum magnet • If this next closest magnet is common to 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 for PEP-II).

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.

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).

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

10. 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 1.96 1.51 A HER current 1.32 1.13 A y* 12.5 6.5 mm x* 25 60 cm X emittance 50 20 nm-rad Estimated sy* 5 2.2 mm Bunch spacing 1.26 2.4 m Number of bunches 1317 1284 Collision angle head-on 11 mrads Beam pipe radius 2.5 1.5 cm Luminosity 7.21033 11.31033 cm-2 sec-1

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

12. 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*12.58.56.51.5 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12-14 mrads • Beam pipe radius 2.5 2.5 2.5 1.5-2.0? cm • Luminosity 6.61033 1.81034 3.3103411036 cm-2 sec-1

13. 1st attempt • Present PEP-II beam energies • 9 GeV and 3.1 GeV • Symmetric optics Generates upstream SR fans • +/- 12 mrad crossing angle (a la KEK) • Must have a crossing angle. Very difficult if not impossible to have 3400 bunches (1st parasitic crossing is at 31.5 cm from the IP) without a crossing angle. • In addition, the radiation fans from B1 type magnets would become very intense at these high beam currents.

16. 2nd attempt • KEK beam energies • 8 GeV and 3.5 GeV • Lowering the energy ratio improves the SR fans at the IP. The upstream fans are further away from the beam pipe allowing for a smaller radius pipe. • Symmetric optics • +/- 12 mrad crossing angle (a la KEK)

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

20. 3rd attempt • Asymmetric optics (again a la KEK) • The upsteam QD1 magnet for the LER is essentially on axis • The magnet locations are still symmetric (+/-Z) • Still have some upstream bending but the fans are greatly reduced from the previous symmetric optics case. The main SR fans still clear the local IR. • +/- 14 mrad crossing angle • The larger crossing angle is needed to keep the QF2 magnet at the 2.5m point from the IP • This large a crossing angle opens up the possibility of filling all 6800 bunches if the RF freq. is doubled

22. A 1 cm radius beam pipe might be possible now

23. 4th attempt (to be continued) • Detector magnetic field axis • This constraint has not been added in yet. In order to minimize the torques on the QD1 magnets these two magnets need to be aligned with the detector magnetic field. The average axis of the two magnets is then the detector axis.

24. Summary A super B-factory IR is quite challenging The very high beam currents rule out designs in which SR fans are intercepted locally The IR design in the areas of detector backgrounds, HOM power and SR quadrupole radiation are all very difficult and need to be thoroughly studied. The trick is to find a solution that satisfies all of these requirements without compromising the physics