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

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

Machine Parameters

Parameters used in the IR Parameter HER LER Energy (GeV) 7 4 Current (A) 2.12 2.12 Beta X (mm) 20 32 Beta Y (mm) 0.32 0.20 Emittance X (nm-rad) 1.60 2.56 Emittance Y (pm-rad) 4.0 6.4 Sigma X (m) 5.66 5.66 Sigma Y (nm) 38 36 Crossing angle (mrad) +/- 30

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

IR geometry

Detector Reference Frame

The Present Design

Larger view

Improvement details Old New QD0 HER/LER HER/LER QF1 R inside (mm) 24.0/31.5 22.5/32.5 R outside (mm) 28.0/35.5 28.5/38.5 Length (m) 0.40 0.40 Dist to IP (m) 0.58 0.60 Gradient (T/cm) -1.192/-0.522 -1.025/-0.611 Field at inside radius (T) 2.80/1.61 2.31/1.99 Maximum y (m) (sqrt) 1970(44)/2193(47) 1550(39)/2566(51) QF1 R inside (mm) 50.0 50.0 R outside (mm) 56.0 60.0 Length (m) 0.30 0.30 Dist to IP (m) 1.60 1.80 Gradient (T/cm) 0.726/0.399 0.640/0.358 Field at inside radius (T) 3.48/1.92 3.20/1.79 Maximum x (m) (sqrt) 580(24)/200(14) 799(28)/486(22)

Vertical View – same as before

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

QF1 cross-sections

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

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

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

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

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)

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

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

Pictures from Vobly’s paper

The quads can be on axis with the beams

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

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 1.8-2.1m from the IP)

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).

Super-ferric design details PM slices Inside face Length K value Comments LER 0.36 0.02 -5.9959 on beam axis 0.38 0.02 -6.7453 on beam axis HER 0.42 0.18 -4.2827 on beam axis

More details (work in progress) QDO twin magnets Starts 0.7 m from the IP – 0.4 m long Gradient 0.546 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 0.428 T/cm – max field ~1.3 – 1.5 T

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 0.333 T/cm 1.2-1.4 T HER 0.647 T/cm 2.4-2.6 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.

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.

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

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.

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.

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

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…