The SuperB Accelerator Lattice M. E The SuperB Accelerator Lattice M. E. Biagini, LNF-INFN for the SuperB Accelerator Team 2nd IRC Meeting Rome, April 29th 2008

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

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)

Evolution of lattice (1) Several accelerator issues have been addressed after completion of the CDR. In particular: Power consumption Costs Site requirements Beam parameters Crab waist compensation Optimization of ring cell and Final Focus QD0 quadrupole design Touschek backgrounds (see Uli’s talk) Polarization schemes (see Uli’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

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) x-emittance vs x-phase advance/cell 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)

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 emittances and b* and equal currents  Present B-factories design SuperB

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 e+ e- LER HER

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

SuperB New Parameters Beam-beam transparency conditions in red

Example of beam-beam tune scans for different schemes D. Shatilov Lifetrack code Blue: bad Red: good 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

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, M. Zobov, IV SuperB Workshop

Luminosity and blow-up vs damping time and Np Nominal damping: 10msec/3Km rings 2.5 times longer 5 times longer 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

Beam-beam blow-up L=1036 cm-2 s-1 D. Shatilov, 2007 New parameteres here LER Crab=0.9Geom_Crab HER Crab=0.8Geom_Crab 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

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

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 Cell #2 Cell #1 LER HER

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

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

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

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

IP layout M.Sullivan 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

S. Bettoni, E. Paoloni

S. Bettoni, E. Paoloni

Rings optical functions LER HER No spin rotator here

Chromatic functions (zoom) FF

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

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

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

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

One ring layout 280 m 20 m No spin rotator here

Conclusions New cell layout is more flexible in terms of emittance, allowing for the same target luminosity of 1036 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 (see Uli’s talk)