1. M. Boscolo, K. Bertsche, E. Paoloni, S. Bettoni,
IR Design Update
M. Sullivan
For
M. Boscolo, K. Bertsche, E. Paoloni, S. Bettoni,
P. Raimondi, et al.
SuperB Workshop XI
INFN, Frascati, Italy
December 1-5, 2009

2. Outline IR Design New Study using Vobly’s Panofsky quads Summary
Same as October workshop
Features
Layout
SR backgrounds
New Study using Vobly’s Panofsky quads
Summary

3. Machine Parameters

4. Parameters used in the IR
Parameter HER LER
Energy (GeV)
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

5. General IR Design Features
Crossing angle is +/- 30 mrads
Cryostat has a complete warm bore
Both QD0 and QF1 are super-conducting
PM in front of QD0
Soft upstream bend magnets
Further reduces SR power in IP area
BSC to 30 sigmas in X and 140 sigmas in Y (10 sigma fully coupled)
Do NOT want to design out upgrades

6. IR geometry

7. Detector Reference Frame

8. The Present Design

9. Larger view

10. Improvement details Old New QD0 HER/LER HER/LER QF1
R inside (mm) / /32.5
R outside (mm) / /38.5
Length (m)
Dist to IP (m)
Gradient (T/cm) / /-0.611
Field at inside radius (T) / /1.99
Maximum y (m) (sqrt) 1970(44)/2193(47) (39)/2566(51)
QF1
R inside (mm)
R outside (mm)
Length (m)
Dist to IP (m)
Gradient (T/cm) / /0.358
Field at inside radius (T) / /1.79
Maximum x (m) (sqrt) (24)/200(14) (28)/486(22)

11. Vertical View – same as before

12. Beam sizes in QD0
Beams in the PM slices
45 mm dia.
65 mm dia.

14. QF1 cross-sections

16. 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
Photons from particles at high beam sigmas presently strike within 5-6 cm downstream of the IP
However, highest rate on the detector beam pipe comes from a little farther away
Unlike PEP-II, the SuperB design is sensitive to the transverse beam tail distribution

17. SR from the upstream bends
B1 magnet
Kc = 4.0 keV
B1 magnet
Kc = 0.7 keV

18. SR power from soft bends
B0 magnet
Kc = 1.2 keV
B0 magnet
Kc = 0.2 keV

19. SR photon hits/crossing
LER
HER
748
215
1600
5300
4.4E4
1E4
1.3E6
1.1E5
7.5E5
1.8E7

20. SR photon hits/crossing on the detector beam pipe from various surfaces
LER
HER
0.24
0.07 10 13
111 13 8 9
968
105
Backscattering SA and absorption rate (3% reflected)

21. SR to do list A 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

22. New Idea – Super-ferric QD0
Pavel Vobly from BINP has come up with a new idea for QD0 (mentioned at the end of the last workshop)
Use Panofsky style quadrupoles with Vanadium Permendur iron yokes
This new idea has some added constraints but it is still attractive because it is easier to manufacture and the precision of the iron determines the quality of the magnet

23. Pictures from Vobly’s paper

24. The quads can be on axis with the beams

25. Super-ferric QD0 Extra constraints
Maximum field of no more than 2T at the pole tips
Equal magnetic fields in each quad
Square apertures
Might be able to relax these a little
If we have room between the windings to add Fe then we can have some magnetic field difference
Might be able to make the apertures taller than they are wide – means the windings get more difficult
For now assume constraints are there and then see what we can do

26. First approximation design
Need to back up QD0 to make more space in front to add PM slices to the HER (toward getting the magnetic fields equal and to increase the space between the beams)
Moved QD0 back 10 cm (face is 70 cm from the IP)
Added 5 more 2 cm long PM slices to the HER
Still not enough to get the fields equal
Added another smaller defocusing quad to the HER behind the twin magnets
This quad has no partner and uses all of the space between the beams for the iron yoke to absorb the stray field at the nearby LER
Also moved QF1 farther back 20 cm (now at m from the IP)

27. Some consequences
Beta^ (maximum betas) are bigger for both beams both planes
Horizontal beam-stay-clear has gotten much larger in QF1
The detector magnetic field must be carefully compensated out (also true for the baseline QD0s and QF1s).

28. Super-ferric design details
PM slices
Inside face Length K value Comments
LER
on beam axis
on beam axis
HER
on beam axis

29. More details (work in progress)
QDO twin magnets
Starts 0.7 m from the IP – 0.4 m long
Gradient T/cm
Aperture 42 mm X and Y
Maximum field ~1.2 – 1.4 T
4 mm of space for the conductors
QD0H
An added defocusing quad for the HER
Starts 1.15 m from the IP (5 cm between QD0 and QD0H) and is 0.25 m long
There looks to be enough space between beams now for this to be a separate magnet (the iron can be made thick enough to shield the nearby passing LER). Needs to be checked further.
Aperture 60 mm X and Y
Gradient T/cm – max field ~1.3 – 1.5 T

30. Still more details QF1 Starts at 2.0 m from the IP – 0.3 m long
Aperture – about 80 mm
Gradients and max field
LER T/cm T
HER T/cm T
The HER field strength is too high and the HER – LER field strengths are different. We cannot use a super-ferric design for QF1 because we don’t have enough space between the beams to have separate magnets. We could use the Italian design for QF1.

31. Design constraints
The requirement of the maximum field strength to be less than 2 T has forced us to move the magnets back from the IR, but this also makes the beam size increase which is one of the reasons the QF1 aperture is so large.
The requirement of a square aperture does not seem to cause any problems so far. We seem to be dominated in aperture in the X plane instead of in the Y plane.

32. SR backgrounds for the Super-ferric QD0
We tested the case of putting all of the magnet centers on beam axis which we can do in the super-ferric design
Unfortunately the straight on-axis solution generates SR photons from the high-sigma region of the beam profile that directly strike the detector beam pipe
These photons come from the beam rays with the steepest slope out of QF1
Both the current baseline design and the super-ferric design must have offset QD0 axes

33. SR rates for the super-ferric case with beams on magnet axes
LER
HER
1.1E4
2.5E6
6.9E6
1.2E5
8E5
1.7E4
2.1E5
2.1E6
4.3E6
2.3E7
1.4E5
Apologies. This is the basic design picture. Beampipe geometry is the same.

34. SR rates for super-ferric case with offset QD0s
LER
HER
8.9E5
3.3E7
5.1E4
3.9E7
1.1E5
7E8
Apologies. This is the basic design picture. Beampipe geometry is the same.

35. Summary The present baseline design IR is holding
All the magnets inside the detector are either PM or SC
The beam pipes inside the cryostats are warm
We (still) 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

36. Summary (cont.)
Taken a first look at a super-ferric solution using Panofsky style quads
Extra constraints make finding a solution more difficult
But the slimplicity of construction and the possibility of decoupling some of the magnetic elements make the idea attractive
First attempt almost works. QF1 becomes a problem. Need to try a few more variations…