Evolution of Lattice for the SuperB Accelerator: Layout, Simulations, and Conclusions

1. The SuperB Accelerator LatticeM. E. Biagini, LNF-INFNfor the SuperB Accelerator TeamSuperB MeetingElba, May 31th 2008

2. Outline • Evolution of lattice • SuperB transparency conditions • Beam-beam simulations • Layout of rings and Final Focus • Dynamic aperture • Conclusions

3. SuperB Accelerator Contributors • M. E. Biagini, M. Boscolo, A. Drago, T. Demma, S. Guiducci, M. Preger, • P. Raimondi, S. Tomassini, C. Vaccarezza, M. Zobov (INFN/LNF, Italy) • Y. Cai, A. Fisher, S. Heifets, A. Novokhatski, M.T. Pivi, J. Seeman, M. Sullivan, U. Wienands, W. Wittmer (SLAC, US) • T. Agoh, K. Ohmi, Y. Ohnishi (KEK, Japan) • I. Koop, S. Nikitin, E. Levichev, P. Piminov, D. Shatilov (BINP, Russia) • Wolski (Liverpool University, UK) • M. Venturini (LBNL, US) • S. Bettoni (CERN, Switzerland) • A. Variola (LAL/Orsay, France) • E. Paoloni, G. Marchiori (Pisa University, Italy)

4. Evolution of lattice (1) • Several accelerator issues have been addressed after completion of the CDR. In particular: • Power consumption • Costs • Site requirements (see Tomassini’s talk) • Beam parameters • Crab waist compensation • Optimization of ring cell and Final Focus • QD0 quadrupole design (see Bettoni’s talk) • Touschek backgrounds (see Boscolo’s talk) • Polarization schemes (see Wienands’s talk) • The evolution of the lattice design is a consequence of the effort in minimizing costs and power consumption • Arcs design was further optimized in order to: • improve chromatic properties • increase dynamic aperture • decrease intrinsic emittance

5. x-emittance vs x-phase advance/cell Evolution of lattice (2) • Natural emittance decreases further by increasing the arc cell mx, and nominal values can be obtained even without inserting wigglers • Dynamic aperture shrinks with larger mx, but is still large enough (Final Focus is the dominant factor) • Reduced ring length and symmetry to: • 4 “arcs”, 14 cells/arc • Only 2 wiggler straights, 40 m long, empty in Phase I (no wigglers needed) • One Final Focus section • One long straight for RF, injection (beams will be vertically separated here) • Two spin rotator sections (matching in progress)

6. SuperB transparency condition • To have equal tune shifts with asymmetric energies in PEP-II and KEKB the “design” beam currents ratio was: I+/I- ~ E-/E+ • Due to SuperB large crossing angle, new conditions are possible: LER and HER beams can have different emittancesandb* and equal currents  Present B-factories design SuperB

7. e+ e- LER HER New transparency condition We want  • LER sees a shorter interaction region, (4/7 of the HER one) • LER has a smaller by*, easier to acheive in the Final Focus • LER has larger emittance, 2.8 nm, better for Tousheck effect and tolerance to instabilities

8. New transparency condition (2) • Both beam lifetimes are increased (larger emittances), injection rates reduced • Beam-eam simulations show good results, no blow up is seen for HER, 1-3% for LER, but some more optimization is possible: tunes, crabbing (L=1036 is still predicted) • Upgrade parameters can be implemented in any order: - decrease the emittances first, or... - increase the bunch charge, or... - increase the number of bunches, or... - decrease the bunch length • Less RF Voltage is needed

9. Beam-beam transparency conditions in red SuperBNewParameters

10. Example of beam-beam tune scans for different schemes D. Shatilov (BINP) Lifetrack code Blue: bad Red: good Black: very bad y=0.07 y=0.07 Head-on, Lmax = 2.45·1034 Ordinary crossing, Lmax = 2.05·1034 y=0.17 SuperB Large , CW = 0, Lmax = 1.6·1035 Crab Waist, Lmax = 1.05·1036

11. Beam tails and Luminosity vs Crab sextupole strength CDR parameteres here y= 0.183 s= 16 msec y= 0.212 s= 12 msec Ax = (0 : 20)sx Ay = (0 : 50)sy D. Shatilov (BINP), M. Zobov (LNF), IV SuperB Workshop

12. Nominal damping: 10msec/3Km rings 2.5times longer 5 times longer Luminosity and blow-up vs damping time and Np CDR parameteres here Np = 2.5 x 1010 Ax x Ay = 15 sx x 20 sy Np = 5.0 x 1010 Ax x Ay = 25 sx x 80 sy D. Shatilov, M. Zobov, IV SuperB Workshop

13. Crab=0.9Geom_Crab Crab=0.8Geom_Crab LER HER Beam-beam blow-up D. Shatilov (BINP) New parameteres here No blow up is seen for HER, 1-3% for LER, but some more optimization is still possible: tunes, crabbing... L=1036 cm-2 s-1

14. The Rings • Same length and similar lattice, low emittance lattice inspired by ILC Damping Rings • HER, 7 GeV,ex = 1.6 nm, ts = 19.8 msec • LER, 4 GeV,ex = 2.8 nm, ts = 19.5 msec • HER cells host 2 x 5.4 m long PEP-II dipoles • LER cells host 4 x 0.45 m long PEP-II dipoles • Final Focus design NLC-like, with 18 HER-type bends • Rings cross in one Interaction Point with a 48 mrad horizontal crossing angle • Two regions allocated to spin rotators • Circumference scaled down to shortest possible • Rings lattice based on recycling PEP-II hardware (save a lot of money !) • Total power: 17 MW, lower than PEP-II

15. Cell #1 Cell #1 Cell #2 Cell #2 New layout • Alternating sequence of two different arc cells: • mx = p cell, that provides the best dynamic aperture, • mx = 0.72 cell with much smaller intrinsic emittance, which provides phase slippage for sextupoles pairs, so that one arc corrects all phases of chromaticity. • chromatic function Wx < 20 everywhere • b and a variation with particle momentum are close to zero • larger dynamic aperture LER HER

16. Final Focus • SuperB FF requirements different from the ILC-FF • needs geometric aberrations small, sextupoles should be uninterleaved • bends not needed to be weak (smaller synchrotron radiation) • bends should all have the same sign, to avoid chicanes (to keep the geometry simple) and help to reduce the arc length • FF design complies all the requirements in terms of high order aberrations correction • Needs to be slightly modified for LER to take care of energy asymmetry • NLC-like solution was chosen, since has better bandwidth and smaller FF emittance growth

17. Final Focus • Crab sextupoles included in the design, give about 30% reduction in Dynamic Aperture • Two additional sextupoles at the IP phase cancel the 3rd order chromaticity providing an excellent bandwidth.Since they are placed at a minimum betas location, they do not reduce the dynamic aperture • Geometric aberrations reduced, added a x-sextupole to cancel residual geometric aberrations from off-phase sextupoles • Radiative Bhabhas hitting the IR beam pipes are a lot • Sychrotron radiation power is large • A solution with a septum QD0 is being studied

18. Crab sextupoles Final Focus optical functions (Öb) LER:bx* = 35 mm, by* = 220 m HER: bx* = 20 mm, by* = 390 m

19. Chromatic functions bx byx10-3 Min. by @ IP phase becomes a max. for off momenta particles SD SD SF SF SD crab SF SF Off energy behaviour Bandwidths ay ax

20. M.Sullivan, SLAC M. Sullivan’s talk, Joint Accelerator-Detector session on Sunday IP layout • QD0 is common to HER and LER • QD0 axis displaced toward incoming beams to reduce synchrotron radiation fan on SVT • Dipolar component due to off-axis QD0 induces, as in all crossing angle geometries, an over-bending of low energy out-coming particles eventually hitting the pipe or detector • New QD0 design based on SC “helical-type” windings

21. S. Bettoni, E. Paoloni S. Bettoni’s talk, Joint Accelerator-Detector session on Sunday

22. Rings optical functions LER HER No spin rotator here

23. Chromatic functions (zoom) FF

24. Dynamic Aperture optimization (1) • Dynamic Aperture (DA) represents the stability area of particles over many turns. It depends on lattice non-linearities, mainly the sextupoles used for chromaticity correction • Large chromaticity and strong sextupoles are a characteristics of very low emittance lattices • The Tousheck lifetime is affected by it • It is very important to have a large stable region possibly for different working points (WP) in the tunes plane • It is also important that a good DA WP corresponds to good beam-beam WP ! • For low symmetry lattices, as SuperB, a dense net of structural resonances arises

25. Dynamic Aperture optimization (2) • For SuperB a large perturbation comes from the Final Focus region, where strong sextupoles are used to correct the large chromaticity produced at the IP, and where the CW sextupoles are placed • Very nice work for SuperB HER has been performed at BINP (P. Piminov) with the Acceleraticum code which allows for optimization of DA and WP at the same time • The method is called “Best sextupole pair” (BSP) • A DA tune scan and matching of the tune WP is performed • Work is still in progress and will continue for off-momentum DA, as well as for the LER. DA with the inclusion of machine errors need also to be computed P.Piminov, BINP

26. New WP (.569/.638) New WP (.569/.638) Old WP (.575/.595) Old WP (.575/.595) Horizontal DA Vertical DA SuperB HER DA tune scan Blue: bad Red: good Cross check of DA and luminosity tune scans is very important Iterative method allows to choose best WP for both P.Piminov, BINP

27. HER DA optimization for new WP 130 σy 80 σx Black: original DA at WP (.575/.595) Red: optimized at WP (.575/.595) Green: DA for the new WP (.569/.638), same sextupoles Blue: DA re-optimized in the new WP (.569/.638) P.Piminov, BINP

28. 20 m 280 m One ring layout No spin rotator here

29. Conclusions • New cell layout is more flexible in terms of emittance, allowing for the same target luminosity of1036 cm-2 s-1 • Rings are shorter and cheaper • Longer Tousheck lifetime in LER • Lower vertical tune shift • More relaxed LER beam parameters • Lower currents • Longer damping times • Possible to run Phase #1 without wigglers • Upgrade parameters possible with wiggler installation • All PEP-II magnets used • Final Focus design to be optimized for backgrounds • Dynamic aperture optimization in progress • Space for spin rotators provided, matching into lattice in progress (U. Wienands’s talk, next)