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

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

Machine Parameters Originally Used

Present Parameters

Parameters used in the IR Design Parameter HER LER Energy (GeV) 6.70 4.18 Current (A) 1.89 2.45 Beta X (mm) 26 32 Beta Y (mm) 0.253 0.205 Emittance X (nm-rad) 2.00 2.46 Emittance Y (pm-rad) 5.0 6.15 Sigma X (m) 7.21 8.87 Sigma Y (nm) 36 36 Crossing angle (mrad) +/- 33

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)

General Reference Frame

The Present Baseline Design

Larger view

Vertical View – same as before

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 These are somewhat out of date.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.

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

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.

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)

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

Resonance Upsilon 4S Upsilon 3S Upsilon 2S Upsilon 1S Ecm (GeV) 10.5794 10.3554 10.0236 9.4609 HER E (GeV) 6.694 6.553 6.343 5.988 QD0 (T/cm) -0.97584 -0.95329 -0.91969 -0.86285 QF1 (T/cm) 0.60408 0.59132 0.57232 0.54019 LER 4.18 4.091 3.96 3.737 -0.63941 -0.62522 -0.60435 -0.56882 0.37412 0.36616 0.35445 0.33450 QD0 ratio 1.52617 1.52472 1.52179 1.51693 QF1 ratio 1.61466 1.61491 1.61469 1.61490  1.02785 1.02787 1.02791 Boost () 0.23763 0.23773 0.23775 0.23793

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

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

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

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

Pictures from Vobly’s paper

The quads can be on axis with the beams

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

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)

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

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 14-14.5 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 (0.17-0.21 m) These magnets bend the beams slightly out in X increasing the beam separation for the other magnets LER beam 1.864 mrad HER beam 1.164 mrad

Details of the permanent magnet slices Z from IP Len. R1 R2 G Name Beam m cm mm mm T/cm QDSA both 0.17 2 13 28 1.076 QDSB both 0.19 2 14 30 0.994 QDPA LER 0.30 1 7.5 12.5 1.392 QDPB LER 0.31 1 7.5 13.0 1.473 QDPC LER 0.32 1 7.5 13.5 1.547 QDPD LER 0.33 1 7.5 14.0 1.616 QDPE LER 0.34 1 7.5 14.5 1.680 QDPF LER 0.35 1 7.5 15.0 1.740 QDPG LER 0.36 1 7.5 15.5 1.796 QPDH drift 0.37 1 QDPI HER 0.38 1 7.5 16.5 1.899 QDPJ HER 0.39 1 7.5 17.0 1.945 QDPK HER 0.40 1 7.5 17.5 1.989 QDPL HER 0.41 1 7.5 18.0 2.030 QDPM HER 0.42 1 7.5 18.5 2.070 QDPN HER 0.43 1 7.5 19.0 2.107 QDPO HER 0.44 1 7.5 19.5 2.142 QDPP HER 0.45 1 7.5 20.0 2.175 QDPQ HER 0.46 1 7.5 20.5 2.207 QPDR HER 0.47 1 7.5 21.0 2.238 QDPS HER 0.48 1 7.5 21.5 2.266

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 16.17 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

Vanadium Permendur Design

VP Design details PM as described above Magnet QD0 QD0H QF1 QF1H IP face (m) 0.55 0.90 1.25 1.70 Length (m) 0.30 0.15 0.40 0.25 G (T/cm) 0.938 0.707 0.407 0.381 Aperture (mm) 33 49 75 77 Max. Field (T) 1.688 1.732 1.526 1.467 X offset (mm) 2.3/2.0 1.8 0.5/1.0 1.0 X angle (mrad) 15 17 20 0.7

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

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 8.80 64.8 26.3 40.2 0.231 481 746 1000 Dy 8.55 61.4 24.7 40.5 0.247 540 500 120 Ga 7.90 54.8 21.8 37.9 0.259 570 --- <120 Fe 7.87 211 82 170 0.29 608 590 0.4 (scrap) Pb 11.35 16 5.6 46 0.44 --- 38.3 2 Sn 7.31 50 18 58 0.36 --- 51 18 Cu 8.96 120 48 140 0.34 369 874 15 Ni 8.90 200 76 180 0.31 638 700 18 Al 2.70 70 26 76 0.35 167 245 21 Au 19.30 120 27 180 0.44 216 --- 34,000 Zn 7.13 108 43 70 0.25 --- 412 2 Ag 10.50 83 30 100 0.37 251 25 530 *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

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

Holmium design details PMs as described above Magnet QD0 QD0H QF1 QF1H IP face (m) 0.55 0.80 1.15 1.45 Length (m) 0.20 0.10 0.25 0.15 G (T/cm) 1.494 1.147 0.727 0.727 Aperture (mm) 34 41 67 68 Max. Field (T) 2.540 2.351 2.435 2.472 L/H L/H X Offset (mm) 1.3/1.5 1.7 0.7/0.0 0.1 X angle (mrad) 17 10 12 1.1

Holmium Design

Beta function comparison with V12 baseline V12 VP Ho LER x max 316 309 221 HER x max 388 480 328 LER y max 1562 1424 1300 HER y max 1266 1208 1111

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

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 100-140 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

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

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…….

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