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 XII
LAPP, Annecy, France
March 16-19, 2010

2. Outline IR Design Update on study of Vobly’s Panofsky quads Summary
CDR2 (white paper) baseline
Features
Layout
SR backgrounds
Update on study of Vobly’s Panofsky quads
Summary

3. Machine Parameters Originally Used

4. Present Parameters

5. Parameters used in the IR Design
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) +/- 33

6. General IR Design Features
Crossing angle is +/- 33 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 100 sigmas in Y (7 sigmas fully coupled)

7. General Reference Frame

8. The Present Baseline Design

9. Larger view

10. Vertical View – same as before

11. Beam sizes in QD0 Beams in the PM slices
45 mm dia.
65 mm dia.
These are somewhat out of date. They use the old machine parameter set.

12. QF1 cross-sections

13. 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

14. Beam Tail Distribution
These tail distributions are more conservative than those used for PEP-II. The SuperB beam lifetime is shorter by about a factor of 10 so the tail distributions can be higher. But we will probably collimate at lower beam sigmas than shown here.

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

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

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

18. 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)

19. Energy Changes
For the QD0 and QF1 magnets we need to keep the ratio of the magnetic field strengths constant in order to maintain good field quality
We want the * values to remain constant to maintain luminosity
We need to match to the rest of the ring
No changes to the permanent magnets
Solutions found by iteration
Solutions found for all Upsilon resonances

20. Resonance
Upsilon 4S
Upsilon 3S
Upsilon 2S
Upsilon 1S
Ecm (GeV)
9.4609
HER
E (GeV)
6.694
6.553
6.343
5.988
QD0 (T/cm)
QF1 (T/cm)
LER
4.18
4.091
3.96
3.737
QD0 ratio
QF1 ratio 
Boost ()

21. Energy Changes
The 2S and the 3S LER energies would have very little polarization
It should be straightforward to develop a procedure to perform an energy scan
To go to the Tau-charm region (Ecm ~4 GeV) we will need to remove most if not all of the permanent magnets
With the air-core super quads we would need to approximately preserve the energy asymmetry
We might be able to get more creative by using the PMs to change the actual beam energies

22. Solenoid compensation
We have recently found out from our colleagues at KEK that we should pay much more attention to the fringe field of the detector solenoid
The radial part of the field causes emittance growth
This also means that we want to minimize the fringing fields of the solenoids
We will need to revisit our compensation schemes and look at ways of minimizing the fringing fields as well as the total integral

23. To do list SR Revisit solenoid compensation
A more thorough study of surfaces and photon rates
Check dipole SR
More detailed backscatter and forward scatter calculations from nearby surfaces and from the septum
Photon rate for beam pipe penetration
Revisit solenoid compensation

24. Super-ferric QD0 and QF1
Pavel Vobly from BINP has come up with a new idea for QD0 (mentioned at 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

25. Pictures from Vobly’s paper

26. The quads can be on axis with the beams

27. Super-ferric QD0 Constraints Might be able to relax these a little
Vobly had a 2 T limit but we need 10% headroom for any above 4S energy scan
Constraints
Maximum field of no more than 1.8 T at the pole tips (we assume this is the same as the half width – should probably lower this limit another 10%-20% because the pole tip is on the diagonal)
Equal magnetic field strengths in each twin 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

28. Permanent Magnets
Upon embarking on the task of looking at the Super-Ferric design we realized we could significantly improve the IR design by improving the permanent magnet performance
Give up some vertical aperture in order to go back to circular magnet designs (~1.4 stronger field)
Open up the crossing angle 10% to get more space for permanent magnet material
Add a couple of permanent magnet slices in front of the septum (shared magnets but close to the IP and hence minimal beam bending)

29. Permanent Magnets (2)
Moved some of the slices previously used on the HER to the LER in order to get more vertical focusing to the LER
We now have more equal vertical beta maximums
The beam pipe inside the magnets is 1 mm smaller in radius
6 mm from 7 mm
The magnetic slices are now only 1 cm long and are perpendicular to the beam line instead of the detector axis
Better packing and better magnetic field performance for each beam

30. Permanent Magnets (3)
With a 6 mm inside radius beam pipe that is 1 mm thick and allowing for 0.5mm of space between magnet material and beam pipe we arrive at a 7.5 mm inside radius for the magnet material
The chosen remnant field of 13.4 kG is conservative. Some materials can reach kG. All materials are Neodymium-Iron.
This gives us some headroom for packing fraction losses between magnetic blocks
There are two shared quad slices on either side of the IP in fairly close ( m)
These magnets bend the beams slightly out in X increasing the beam separation for the other magnets
LER beam mrad
HER beam mrad

31. Details of the permanent magnet slices
Z from IP Len R R G
Name Beam m cm mm mm T/cm
QDSA both
QDSB both
QDPA LER
QDPB LER
QDPC LER
QDPD LER
QDPE LER
QDPF LER
QDPG LER
QPDH drift
QDPI HER
QDPJ HER
QDPK HER
QDPL HER
QDPM HER
QDPN HER
QDPO HER
QDPP HER
QDPQ HER
QPDR HER
QDPS HER

32. Vanadium Permendur Design
We use the above redesigned permanent magnet slices
QD0 face is 55 cm from the IP. If we move in closer the field strength gets too high. In addition, we lose space for the stronger PM slices
We start by setting the LER side of QD0 and QF1
We impose the beta function match requirements for the LER (* and the match point at m) and we also try to get the maximum field close to 1.8 T
We keep the L* value constant but are allowed to change the separation and the lengths of QD0 and QF1
These set the QD0 and QF1 strengths for the HER
Add another smaller defocusing quad to the HER behind QD0 to complete the vertical focusing for the HER
Also add another smaller focusing quad behind QF1 to complete the horizontal focusing of the HER

33. Vanadium Permendur Design

34. VP Design details PM as described above Magnet QD0 QD0H QF1 QF1H
IP face (m)
Length (m)
G (T/cm)
Aperture (mm)
Max. Field (T)
X offset (mm) 2.3/ /
X angle (mrad)

35. Latest New Idea
We have discovered there are several rare earth metals that have very high magnetization curves
Holmium
Dysprosium
Gadolinium
Holmium has the highest magnetic moment of any element and is reputed to have a magnetization curve up to 4 T (Vanadium Permendur is about 2.4 T)
One of the reasons these metals are not used is that they only become ferromagnetic at temperatures well below room temperature (except for Gadolinium)
Curie temperatures
Ho is 20 K
Dy is 85 K
Ga is 289 K

36. Some properties of these metals*
Den. Young’s Shear Bulk Possion Vickers Brinell Cost
Elem. g/cc Mod. Mod. Mod. Ratio Hard. Hard. $/kg Ho Dy
Ga <120
Fe (scrap) Pb Sn Cu Ni Al
Au ,000 Zn Ag
*Wikipedia, Metalprices.com and VWR Sargent Welch
These elements appear to be somewhere between Tin and Aluminum in hardness and strength with a density of Ni or Cu

37. Holmium Design
Set maximum field at 3.2 T which means 2.9 T max to allow for headroom to scan above the 4S
Shorten and bring the magnets closer together to lower beta maximums
Make apertures smaller when possible which allows us to increase the field strength

38. Holmium design details
PMs as described above
Magnet QD0 QD0H QF QF1H
IP face (m)
Length (m)
G (T/cm)
Aperture (mm)
Max. Field (T)
L/H L/H
X Offset (mm) / /
X angle (mrad)

39. Holmium Design

40. Beta function comparison with V12 baseline
V12 VP Ho
LER x max
HER x max
LER y max
HER y max

41. SR backgrounds for the Super-ferric QD0
SR backgrounds have not been checked yet
The outward bending of the beams from the shared quads makes the SR shielding harder
We have some natural inward bending from the QD0 magnets which we need to steer the QF1 radiation away from the central chamber
We may find that the bending from the shared quads causes too much trouble but we would like to keep the option open as it improves the beta functions
SR studies may force some iterations to the design

42. Baseline Summary
The present baseline design for the IR is self-compensating air core dual quad QD0 and QF1 design
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  BSC in Y (7-10 fully coupled)
Synchrotron radiation backgrounds look ok, but need more study
This is the White paper (CDR2) design
Radiative bhabha backgrounds should be close to minimal – nearly minimal beam bending

43. Super- ferric Summary
We are taking a close look at a super-ferric solution using Panofsky style quads
Equal field strengths and square apertures make finding a solution more difficult but there are also self-shielding possibilities
The simplicity of construction and the ability to decouple some of the magnetic elements make the idea attractive

44. Super-ferric Summary (2)
We have also found a rare earth metal (Holmium) that has a very high magnetic moment and consequently a high magnetization curve once the metal gets below its Curie temperature of 20 degK (Dysprosium is also an interesting possibility Curie T = 85 degK)
If we can use this metal we can put much higher magnetic fields in QD0 and QF1 thereby improving the beta functions
We have constructed a Vanadium Permandur design and a Holmium design but neither have yet had the SR backgrounds checked
SR background studies may alter the designs. Work in progress…….

45. Conclusions
The flexibility of the IR design has been improved by re-optimizing the permanent magnets
We have more focusing in closer to the IP now
This improves the baseline design (which hasn’t yet been fully redesigned) as well as the new Panofsky style magnet design
The IR design now has a better chance of making smaller beta* values than the baseline design
We have two working designs for the Panofsky style magnets
Vanadium Permendur
Holmium
These designs still need to be checked for SR backgrounds
The IR design looks robust with the various options under study