1. M. Sullivan International Review Committee November 12-13, 2007
SuperB IR Design
M. Sullivan
International Review Committee
November 12-13, 2007

2. Outline Detector Considerations Accelerator Parameters IR Design
Summary

3. Detector Considerations
Reasonable angular acceptance
±300 mrad
Small radius beam pipe
10 mm radius
Thin beam pipe
Minimum amount of material

4. Detector Considerations (2)
Backgrounds under control SR
Rates comparable to PEP-II
Few hits per crossing on Be beam pipe
Little or no hits on nearby beam pipes
BGB -- coulomb
Keep nearby upstream bending to a minimum
Low vacuum pressure upstream of the detector
Touschek
Collimation

5. Detector Considerations (3)
More backgrounds
Luminosity backgrounds
Beam lifetimes
Radiative bhabhas
Beam-beam
Local HOM power
Small diameter beam pipes trap higher frequencies
Always get modes when two pipes merge to one
PEP-II and KEKB experience can help the design

6. Accelerator parameters
LER HER
Energy (GeV)
Current (A)
No. bunches
Bunch spacing (m)
Beat x* (mm)
Beta y* (mm)
Emittance x (nm-rad)
Emittance y (pm-rad) 4 4
Full crossing angle (mrad) 34
These parameters constrain or define the IR design

7. Start with Pantaleo’s FF Conceptual Design

8. SR fans when the shared QD0s have no offsets
HER
QDO
QDO
LER
QDO
QDO

9. IR Design The crossing angle is ±17 mrad
The beam pipe diameters are 20 mm at the outboard end of QD0 for both beams (same size as IP pipe)
This leaves enough room (~10 mm) to place a permanent magnet quadrupole and get the required strength (Using Br = 14 kG)
We have placed small bending magnets between QD0 and QF1 on the incoming beam lines to redirect the QF1 SR
The septum QF1 magnets for the outgoing beams are tilted in order to let the strong outgoing SR fans escape
The B0 magnets on the outgoing beams are C shaped in order to allow the SR fans to escape

10. IR design parameters Length Starts at Strength Comments
L* m Drift
QD m m kG/m Both HER and LER
QD0H m m kG/m HER only
B00L m m kG Incoming LER only
B00H m m kG Incoming HER only
QF1L m ±1.45 m kG/m LER only
QF1H m ±1.45 m kG/m HER only
B0L m ±2.05 m kG LER only
B0H m ±2.05 m kG HER only
QD0 offset 6.00 mm Incoming HER
QD0 offset mm Incoming LER

11. SR Power Numbers The total power is similar to PEP-II
SR power in QD0 (kW) for beam currents of 1.44A HER and 2.5A LER
No QD0 offsets SuperB PEP-II
3A on 1.8A
Incoming HER
Incoming LER
Outgoing HER
Outgoing LER
Total

13. Same scale as the picture on the previous slide

15. LER SR fans

16. HER SR fans

17. ±1 meter

18. SR backgrounds
We use a gaussian beam distribution with a second wider and lower gaussian simulating the “beam tails”
The beam distribution parameters are the same as the ones used for PEP-II
We allow particles out to 10 in x and 35 in y to generate SR
Unlike in PEP-II the SR backgrounds in the SuperB are dominated by the particle distribution at large beam sigma, so we are more sensitive to the exact particle distribution out there

19. SR background numbers LER LER 7726 /xing > 10keV
These numbers are for a 4A LER and a 2.2A HER
280 /xing > 10keV
107 /xing > 20 keV
331 /xing > 10keV
125 /xing > 20 keV
HER
HER
Chamber slopes are steep enough to prevent scattered photons from hitting the detector beam pipe

20. More on SR
The ~8000 photons striking the downstream mask tip from the LER have a shot at hitting the detector beam pipe
If we assume a 10% reflection coefficient (we should be able to get it down to 3% or lower) then we have ~800 photons > 10 keV scattered out of the tip surface
A solid angle calculation for the detector beam pipe (±4 cm) from this source point at 10 cm away gives 1.1%
We then have ~8 photons/crossing > 10 keV hitting the detector beam pipe and ~0.14 photons/crossing >20 keV hitting the detector beam pipe

21. Radiative Bhabhas
The outgoing beams are still significantly bent as they go through QD0
Therefore the off-energy beam particles from radiative bhabhas will get swept out
Knowing this, we will have to build in shielding for the detector

22. HER radiative bhabhas

23. LER radiative bhabhas

24. Design with a new QD0
Under study is a new QD0 design where each beam has a separate magnetic field
This allows each beam to be close to on-axis in this shared magnet
Greatly reduces the total bending and hence the total SR produced
Greatly reduces the radiative bhabha background for the detector

25. Possible QD0 Design

26. SR background
An added constraint of the new design is to keep SR power very low on the cold bores of the QD0 magnets
The beams are very close (6 mm) to the cold bore magnets
The small emittances help and the lower beam currents help
Ended up having to bend the incoming HEB a little to redirect the SR away from the QD0 inner bore and the detector beam pipe

27. Expanded Layout of the IR

28. SR power numbers again The total power is much lower
SR power in QD0 (kW) for beam currents of 1.44A HER and 2.5A LER
No QD0 offsets SuperB PEP-II New
3A on 1.8A QD0
Incoming HER
Incoming LER
Outgoing HER
Outgoing LER
Total

29. SR summary for new design
The overall SR power coming out of the IP is much lower
Keeping the SR off of the QD0 cold bores is an added constraint
The lower beam emittances help
The SR masking has to be fairly tight because the beam is close to the QD0 magnet
A very preliminary design has a comparable background rate for the detector from SR
The beam bending has been greatly reduced. The radiative bhabha background should be also greatly reduced if not eliminated
Further optimization will improve the design

30. Touschek Background and Lifetime M. Boscolo
preliminary results with the latest lattice
(ex=2.8 nm; sz=5 mm; Ib = 1.5 mA)
M. Boscolo
Touschek lifetime with no collimators
tTOU ≈ 12.5 min
in agreement with evaluation from parameters scaling from CDR lattice
trajectories of particle losses
close to the IR
particle losses at IR ≈ 4 KHz/ bunch
essentially downstream the IR
with a preliminary set of collimators inserted at: -86, -60, -47 m far from IP
20x lower
with this preliminary collimators set
lifetime reduced by 30%
work in progress to optimize collimators
for best longitudinal position along the ring and
best trade-off between IR losses and lifetime

31. Summary
We have an IR design that has acceptable SR backgrounds with a crossing angle of ±17 mrad and an energy asymmetry of 7x4
The QD0 shared magnet is super-conducting
The QD0H magnets can be built with permanent magnet technology – does not rule out super-conducting but the space is small
The strong bending of the offset outgoing beams in the shared QD0 produces a significant amount of SR power but the outgoing magnet apertures can be designed to let the SR escape.
The bending of the outgoing beams also produces radiative bhabha background in the detector—we will need to shield the detector from this radiation source
We are looking at a new design for a QD0 magnet where the beams are not bent. Preliminary studies are very encouraging. Close cooperation with the magnet designers will be needed to insure an optimal design.