1. IR Design Update M. Sullivan For
M. Boscolo, K. Bertsche, E. Paoloni, S. Bettoni,
P. Raimondi, et al.
SuperB General Meeting
Perugia, Italy
June 15-20, 2009

2. Outline The Design of last February Improvements since then
Improvements over July 2008
Layout
Shortcomings
Improvements since then
BSC
SR backgrounds
Beam tail distributions
Detector Solenoid
Always more to do
Summary

3. Design from mini-MAC 2008

4. Some features of this design
First part of QD0 is PM just in front of the cryostat
Cold bore under SC QD0
QD0 design simplified (No QD0H – extra quad for the HEB)
QF1 design also simplified (side by side in the cryostat)
Warm bore under PM slices is smallest aperture and hence can intercept SR power (shields cold bore)
Biggest problem was the cold bore
We could not shield it from upstream bending radiation
Difficult to transition to warm bore – takes up z space

5. Latest Design Improvements
Increased the crossing angle to +/- 30 mrads
Cryostat has a complete 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 (10 sigma fully coupled)
We are using the highest luminosity design parameters
Lowest beta* values and highest emittances
Do NOT want to design out upgrades

6. The Present Design (nearly)

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

8. Inside the detector

9. Some more details Lengthened QD0
Increases the magnet aperture 
QD0 strength was getting too high
Maintaining the gradient below 1.2 T/cm 
Increased the space for the QF1 cold mass (from 4 mm to 6 mm) 
Added a shared quad as part of QD0
Starting design parameter for a warm bore design is that 5 mm is enough radial space between the cold mass and room temperature
Had an engineer confirm that this is ok
E. Paoloni

10. 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 through a small “s” bend by these quads because the beam goes through at a 30 mrad angle
Depends on where the quad axis is w.r.t. the beam trajectory
Have studied a case for tilted axis QD0 and QF1 magnets for SR backgrounds. About as good as this design. Magnet apertures can be smaller if we can align the magnets along the beam axis.
For now we will stay with the parallel axes design

11. 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

12. Close up of QD0 beam orbits
The net bending angle is 1.54 mrads
LER coming into QD0
The SR bending power from QD0 is 2x489 W for a 2A beam
QD0 axis
LER outgoing

13. Permanent Magnets
K. Bertsche designed the PM slices
The permanent magnets start the vertical plane focusing for the LER
With the increased 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 (NeB is the material)

14. Vertical View

15. 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

16. Magnet parameters Quad G (kG/m) L(m) to IP (m) Bmax (T)
QD0L (1.61)
QD0H
QF1L
QF1H
Dipole B (kG) L(m) from IP (m)
B0L
B0H

17. Latest improvements since Orsay
BSC interference fixed
More help
SR backgrounds recalculated
New QD0 offsets
First look at backscatter rates
Beam tail distribution
Detector solenoid compensation

18. Vertical BSC Discovered at Orsay
We realized that the LER BSC envelope is higher than it is wide. This means the beam pipe gets too close to the cold mass at the beginning of QD0 in the vertical – closer than 5 mm
The inside diameter of QD0 is 47 mm
We ended up having to increase the size of the LER QD0. The inside diameter is now 62 mm.

19. Too close
47 mm dia.

21. 62 mm dia.

23. SR backgrounds No photons strike the physics window
We trace the beam out to 20 X and 45 Y
The physics window is defined as +/-4 cm for a 1 cm radius beam pipe
The work done for Orsay was redone and an error found
The error was found by Achim Weidemann who is helping with the SR background calculations
This necessitated redoing the first order calculations which forced shifting the QD0 magnetic axes to steer the SR away from the physics window
Photons from particles at high beam sigmas presently strike within 5 cm downstream of the IP
Unlike PEP-II, the SuperB design is sensitive to the transverse beam tail distribution
More on these

24. SR from the upstream bends

25. SR power (Watts)
1175
394
1209
105
209 18
745
9372
446

26. Photons/beam bunch
2.5e6
2.9e7
6.9e5
9.9e6
15680
5.7e5

27. SR backscatter estimates
First order look at backscattering
Resurrected at little program to calculate solid angle fractions from a source of photons to the IP beam pipe
Estimate backscatter rate from a surface using 3% of the incident rate and assuming that it is isotropic
Then calculate SA fraction to IP
This is a decent first order approximation and it is conservative

28. Backscattered photons/beam bunch inc. on Be >10 keV
15680
5.7e5 3 19
241 69

29. Beam tail distributions
Revelation at the Particle Accelerator Conference (May)
Manuela Boscolo calculates the beam lifetime from Touschek scattering and she has now included BGB and Coulomb scattering into her code
She introduces collimators to minimize backgrounds in the detector from these processes
She therefore has the large-sigma beam-tail distribution for the machine to an accuracy of something like a factor of 2
This distribution is exactly what we need for an accurate calculation of SR from beam tail particles near the IP
We are presently using a best guess from PEP-II which should be pretty good but Manuela’s distribution is much closer to the actual beam particle distribution

30. SR to do list More thorough study of surfaces and photon rates
More detailed backscatter and forward scatter calculations from nearby surfaces and from the septum
Photon rate for beam pipe penetration
Orbit deviation study
Beam tail distribution study
Working on acquiring some help for this work

31. Detector solenoid compensation
We have taken a first look at detector solenoid effects on the beam orbit
The large crossing angle means the detector field strongly affects the beams
From a coupling point of view we probably need to cancel as much of the integral B.dl as we can
Most other IRs (KEKB and BEPCII) try to fully compensate the detector field
K. Bertcshe has been cross-checking my code
Work in progress…

32. BaBar detector field Assume the IP is same location as PEP-II
Bz along the Z axis
The dotted lines are where QD0 and QF1 are located
The asymmetric magnetic field complicates any compensation scheme

33. Detector field only – Right side
Incoming LER
This study starts the beams at the IP.
The no detector field orbit is a straight line along y=0.
Outgoing HER

34. Detector field only– Left side
A little better because the total B.dl on the left side is lower.
Outgoing LER
Incoming HER

35. Try to cancel the entire B.dl
Version P6 (K. Bertsche)
Have a separate winding between the two solenoids over QD0 and QF1
Added a solenoid outboard of QF1 to include more detector field
Put in a small short solenoid in front of QD0 to cancel more of the field between the QD0 magnets closer to the IP (similar to KEKB and BEPCII)
Takes up most of the space out to the 300 mrad line for the physics window

36. P6 layout 4L 3L 2L 2R 3R 4R 1L 1R 0L 0R

37. P6 compensation – low field at quads

38. Version P6 orbits – Left side
Left side of IR
Maximum orbit deviation is about 1 mm.

39. P6 orbits – Right side Right side of IR
Maximum orbit deviation is about 0.4 mm.

40. P6 compensation (best for orbit)
There is more B.dl left over

41. P6 best orbits – Left side

42. P6 best orbits – Right side
The orbits are indeed better
Both solutions have good orbits – we also have a solution without the inside compensators

43. Engineering to do list How do we build QD0? How do we build QF1?
Transition space from warm bore to cold magnet wires
Magic flange locations (CESR, KEK and BEPCII have done it)
Not so magic. BEPCII can remove a cryostat before disconnecting the beam pipe
Not possible for us. Will discuss implications in MDI session
Bellows location to relieve stress on detector Be beam pipe
Cryostat supports
Vacuum supports
Where can we put pumping?
Vibration compensated magnet supports ……
Being studied at INFN Pisa and at CERN
First look at this from SLAC

44. People
We have one cryo engineer looking at the small transistion space between the cold magnet and the warm bore. His preliminary report looks quite encouraging. Heat leak rates of 2-3 W/m2 which in his words is “reasonable”.
We will have another cryogenics engineer coming on board in July to study the overall cryostat construction including forces etc.
We have some time from a mechanical designer
Achim Weidemann is helping with SR background study

45. Some Designer Drawings

46. Summary The present IR design is slowly improving
All the magnets inside the detector are either PM or SC
The beam pipes inside the cryostats are warm
We have a 30 BSC in X and 140 BSC in Y (10 fully coupled)
Synchrotron radiation backgrounds look ok, but need more study
Radiative bhabha backgrounds should be close to minimal – nearly minimal beam bending
Designing to the most aggressive machine parameters in order to NOT design them out

47. Conclusions Good progress has been made
Much more to do but the design is firming up
SR backgrounds need more study – these backgrounds drive the actual design
Solenoid compensation is essentially ready for lattice input
We are starting a first order engineering design of the cryostat