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

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

Design from mini-MAC 2008

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

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

The Present Design (nearly)

Comparison to PEP-II Same scale as previous slide

Inside the detector

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

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

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 1.85-4.25=-2.40 mrads HER outgoing

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

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)

Vertical View

Beam parameters used Parameter HER LER Energy (GeV) 7 4 Current (A) 2.00 2.00 Beta X (mm) 20 35 Beta Y (mm) 0.27 0.16 Emittance X (nm-rad) 1.6 2.8 Emittance Y (pm-rad) 4.0 7.0 Sigma X (m) 5.7 9.9 Sigma Y (nm) 33 33 Crossing angle (mrad) +/- 30

Magnet parameters Quad G (kG/m) L(m) to IP (m) Bmax (T) QD0L -522 0.40 0.58 1.23 (1.61) QD0H -1192 0.40 0.58 2.80 QF1L 399 0.30 1.60 1.92 QF1H 726 0.30 1.60 3.48 Dipole B (kG) L(m) from IP (m) B0L -0.77 2.0 6.346 B0H -1.35 2.0 6.346

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

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.

Too close 47 mm dia.

62 mm dia.

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

SR from the upstream bends

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

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

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

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

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

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

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…

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

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

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

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

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

P6 compensation – low field at quads

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

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

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

P6 best orbits – Left side

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

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

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

Some Designer Drawings

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

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