1. M. Boscolo, K. Bertsche, E. Paoloni, S. Bettoni,
IR Design Status
M. Sullivan
For
M. Boscolo, K. Bertsche, E. Paoloni, S. Bettoni,
P. Raimondi, et al.
SuperB Workshop
LAL, Orsay, France
Feb 15-18, 2009

2. Outline Present Design More to do Summary Improvements over July 2008
Layout
Parameters
SR summary
Detector Solenoid
More to do
Summary

3. Do NOT want to design out upgrades
Present Design
After some iterating we have….
Increased the crossing angle to +/- 30 mrads
Cryostat now has a warm bore
Both QD0 and QF1 are super-conducting
PM in front of QD0 for the LER only
LER has the lowest beta Y*
Soft upstream bend magnets
Further reduces SR power in IP area
Increased BSC to 30 sigmas in X and 140 sigmas in Y
Using the highest luminosity design parameters
Lowest beta* values and highest emittances
Do NOT want to design out upgrades

4. Present Design

5. Comparison to PEP-II
Same scale as previous slide

6. Inside the detector

7. Some more details Longer QD0
QD0 strength was getting too high
Maintaining the gradient below 1.2 T/cm
Increased the space for the QF1 cold mass ( 1.75 times)
Added a shared quad as part of QD0
Starting parameter for a warm bore design is that 5 mm is enough radial space between the cold mass and room temperature (needs engineering confirmation)
BSC in X is 30  uncoupled (all of the emittance in the X plane) and in Y we use 20% of the total emittance which is about 140 s
Simona Bettoni will talk on this

8. Parallel axis QD0 and QF1
Presently the axes of the QD0 twin quads are parallel as are the axes of the twin quads of QF1
The beams are bent by these quads because the beam goes through at about a 30 mrad angle
Depends on where the quad axis is w.r.t. the beam trajectory
Have studied on axis QD0 and QF1 magnets for SR backgrounds. About as good as this design.

9. Close up of beam orbits in QD0
We have a double or “S” bend
HER coming into the magnet
QD0 axis
The SR bending power from QD0 is 2x8793 W for a 2A beam
The net bending angle is =-2.40 mrads
HER outgoing

10. Close up of QD0 beam orbits
The net bending angle is =5.40 mrads
LER coming into QD0
The SR bending power from QD0 is 2x1084 W for a 2A beam
QD0 axis
LER outgoing

11. Permanent Magnets
Kirk Bertsche designed the PM slices
The permanent magnets start the vertical plane focusing for the LER
With the larger crossing angle the beams are far enough apart at 0.35 m from the IP to have enough space to install a PM that can work on the LER
The PM quadrupole slices have an elliptical aperture to give us more vertical space
Dimensionally the slices are small
The chosen remnant field is high but not the highest

12. Vertical View

13. Beam parameters used Parameter HER LER Energy (GeV) 7 4
Current (A)
Beta X (mm)
Beta Y (mm)
Emittance X (nm-rad)
Emittance Y (pm-rad)
Sigma X (m)
Sigma Y (nm)
Crossing angle (mrad) +/- 30

14. Magnet parameters Quad G (kG/m) L(m) from IP (m) QD0L -522 0.40 0.58
QD0H
QF1L
QF1H
Dipole B (kG) L(m) from IP (m)
B0L
B0H

15. SR backgrounds No photons strike the physics window
Trace the beam out to 20 X and 45 Y
+/-4 cm for a 1 cm radius beam pipe
Unlike in PEP-II, we are sensitive to the transverse beam tail distributions
Photons presently strike 10 cm upstream and downstream of the IP

16. SR fans from upstream bends

17. SR from the upstream bends

18. SR to do list More thorough study of surfaces and photon rates
Backscatter calculations from nearby surfaces and from septum
Photon rate for beam pipe penetration
Orbit deviation study
Beam tail distribution study

19. Detector solenoid compensation
Just starting to look at detector solenoid effects on the beams
The large crossing angle increases the detector field influence
Starting point is to use the compensating solenoids to correct the beam orbits
Some results for the LER incoming beam

20. BaBar detector field
Bz along the Z axis

21. Compensating solenoids
Plots are scaled to 10 KG (1 T) peak field

22. Orbit before any correction
This study starts the beams at the IP. Detector field-off orbit is a straight line at zero.
Incoming LER
Outgoing HER
Right side of the detector field.

23. Incoming LER corrected with compensation solenoids and added VCOR
Preliminary
Very
1st anti at +15kG
Uncorrected detector at kG
1st & 2nd at +15kG
1st at +20kG & 2nd at +15
1st at +20kG & 2nd at +15 & vcor at 2.8m
Maximum orbit deviation is about 1.5 mm. We want to get this below a mm.

24. More tuning options Can make the compensating solenoids stronger
However we want to keep the field around QD0 and QF1 to a minimum
Extend the second compensator
Cover more of the fringe from the detector field
Adds more integrated compensator field strength
Put a vcor inside the cryostat
Catch the orbit deviation earlier

25. More to do… Solenoid compensating windings are shared with both beams
Need to check both beams and find the best compromise setting
The right side is not equal to the left side – must do the incoming HER and outgoing LER as a separate correction from incoming LER and outgoing HER
Detector field is not symmetric (see detector field plot)
Coupling correction is also different on each side of the IP
Coupling correction may want a yet different setting – need to check coupling against orbit correction setting
Will have to include skew quads in the cryostat

26. Engineering to do list How do we build QD0? How do we build QF1?
Transition space from warm bore to cold bore
Magic flange locations (CESR, KEK and BEPCII have done it)
Bellows location to relieve stress on detector Be beam pipe
Magnet supports
Vacuum supports
Where can we put pumping?

27. Summary
The present IR design has improved since the July machine advisory review
All the magnets inside the detector are now either PM or SC
The beam pipes inside the cryostats are now warm
We now have a 30s BSC in X and 140s BSC in Y
Synchrotron radiation backgrounds look ok, but need more study
Radiative bhabha backgrounds should be close to minimal
Designing to the most aggressive machine parameters in order to NOT design them out

28. Conclusion Good progress has been made
Much more to do but the design is firming up
SR backgrounds need more study
Solenoid compensation needs more work
Very close to starting a first engineering design
Onward!