SLAC Accelerator Department Super-B-Factory John T. Seeman Assistant Director of the Technical Division Head of the Accelerator Department Caltech Meeting December 3, 2004

SLAC Accelerator Department Beam Lines SBF SBF injector needs no changes

SLAC Accelerator Department The PEP-II e + e - asymmetric collider Location of new RF cavities

SLAC Accelerator Department PEP-II HER RF cavities

SLAC Accelerator Department Luminosity Equation  y is the beam-beam parameter (~0.065)  I b is the bunch current (1 to 3 mA)  n is the number of bunches (~1600)  y * is the IP lattice optics function (vertical beta) (10 mm)  E is the beam energy (3.1 and 9 GeV)  Luminosity (10 33 cm -2 s -1 )

SLAC Accelerator Department Achieving Super B Luminosities Higher Currents: oMore rf power, cooling, injector oMore HOM heating (more bunches) oBeam instabilities oElectron clouds, fast ions Smaller  y *: oSmaller physical/dynamic aperture oShorter lifetime, more background Shorter  z : oMore HOM heating oCoherent synchrotron radiation oShorter lifetime, more background Higher tune shifts: oHead-on collisions replaced by angled crossing oDegrades maximum tune shift unless crabbing cavities used

SLAC Accelerator Department PEP-II/BaBar Roadmap: Super B-Factory Study The Roadmap Committee has studied the future of PEP-II and BaBar with a possible large upgrade at the end of the decade. A Super-PEP-II could produce 10 ab -1 per year with a peak luminosity of 7 x /cm 2 /s. Accelerator parameter goals have been set and work towards a solid design has started. The long range time goal is to have a new upgraded accelerator running in 2011 or 2012.

SLAC Accelerator Department PEP-II upgrades schemes Luminosity (x ) 757 RF frequency (MHz)  95 2 Site power (MW)  100 Crossing angleNoYes Crab cavitiesNoYes Replace LERYes Replace HERNoYes UpgradeableNo Yes (to 952MHz) Yes Detector requirements depend on projecting backgrounds for luminosities that are >20 times larger than at present Recommended

SLAC Accelerator Department LER ring (no IR yet) 6 sextants, small negative momentum compaction, using present LER dipoles & quads (16 families), 3 sextupole families Biagini

SLAC Accelerator Department One sextant Biagini

SLAC Accelerator Department One half-arc + dispersion suppressor Biagini

SLAC Accelerator Department Super B-Factory Components Under Study IR SC magnets New RF cavitiesNew IR layout New Arc magnets

SLAC Accelerator Department New IR magnet design (Parker)

SLAC Accelerator Department New IR magnet design Quadrupole, anti- solenoid, skew quadrupole, dipole and trims located in one magnet. All coils numerically wound on a bobbin.

SLAC Accelerator Department Activities towards luminosity upgrade crossing angle 22 mrad Head-on(crab) ◊ ◊ ◊ ◊ ◊ yy (Strong-weak simulation) (Strong-strong simulation) Crab crossing may boost the beam-beam parameter up to 0.2! Superconducting crab cavities are under development, will be installed in KEKB in K. Ohmi K. Hosoyama, et al

SLAC Accelerator Department Electron Cloud Instability & multipacting

SLAC Accelerator Department LER aluminum vacuum system: limit at 4.5A Total LER SR power = 2 MW High power photon stops Antechambers Reduce Electron- Cloud-Instability 4.5 A at 3.1 GeV Photon Stop limits

SLAC Accelerator Department Vacuum system for Super B Factory Antechamber and solenoid coils in both rings. Absorb intense synchrotron radiation. Reduce effects of electron clouds. Circular-chamber Ante-chamber with solenoid field Build-up of electron clouds

SLAC Accelerator Department HOM calculations: 476 MHz cavity 476 MHz cavity with a larger beam opening S.Novokhotski R beam = mm Total loss = V/pC Loss integral above cutoff = V/pC HOM Power = A

SLAC Accelerator Department HOM calculations: 952 MHz cavity 952 MHz cavity with a larger beam opening S.Novokhotski R beam = 47.6 mm Total loss = V/pC Loss integral above cutoff = V/pC HOM Power = A

SLAC Accelerator Department Luminosity-dependent backgrounds oSR in bend & quadrupole magnets oCurrent dependent terms due to residual vacuum oBhabha scattering at IP PEP-II Head-On IR Layout

SLAC Accelerator Department Achieving Super B Luminosities Higher Currents: oMore rf power, cooling, injector oMore HOM heating (more bunches) oBeam instabilities oElectron clouds, fast ions Smaller  y *: oSmaller physical/dynamic aperture oShorter lifetime, more background Shorter  z : oMore HOM heating oCoherent synchrotron radiation oShorter lifetime, more background Higher tune shifts: oHead-on collisions replaced by angled crossing oDegrades maximum tune shift unless crabbing cavities used

SLAC Accelerator Department Power Scaling Equations Synch rad ~ I E 4 /  Resistive wall ~ I 2 total /r 1 /f rf /  z 3/2 Cavity HOM ~ I 2 total /f rf /  z 1/2 Cavity wall power = 50 kW Klystron gives 0.5 MW to each cavity Magnet power ~ gap~r 1

SLAC Accelerator Department Power scaling equations Synch rad ~ I E 4 /  Resistive wall ~ I 2 total /r 1 /f rf /  z 3/2 Cavity HOM ~ I 2 total /f rf /  z 1/2 Cavity wall power = 50 kW Klystron gives 0.5 MW to each cavity Magnet power ~ gap ~ r 1

SLAC Accelerator Department Site power limits 476 MHz 952 MHz (Linac, PEP-II magnets and campus power = 40 MW) 1.5x x x10 34

SLAC Accelerator Department Recommended scenario: 5 to 7 x Replace present RF with 952 MHz frequency over period of time. Use 8 x 3.5 GeV with up to 15.5 A x 6.8 A. New LER and HER vacuum chambers with antechambers for higher power (x 4). Keep present LER arc magnets but add magnets to soften losses; replace HER magnets as well. New bunch-by-bunch feedback for 6900 bunches (every bucket) at 1 nsec spacing. (Presently designing feedback system being nsec spacing.) Push  y * to 1.5 mm: need new IR (SC quadrupoles) with 15 mrad crossing angle and crab cavities

SLAC Accelerator Department Important Factors in Upgrade Direction Project is “tunable” –Can react to physics developments –Can react to changing geopolitical situation Project anti-commutes with linear collider Will emerge from BABAR and Belle, but could be attractive to wider community in context of other opportunities –As we learn more about machine and detector requirements and design, can fine tune goals and plans within this framework Project has headroom –Major upgrades to detector and machine, but none contingent upon completing fundamental R&D –Headroom for detector up to 5 x ; with thin pixels beyond –Headroom for machine up to 8.5 x ; requires additional rf, which can be staged into machine over time

SLAC Accelerator Department Luminosity Equation When vertical beam-beam parameter is limited.  y ~ 0.06 in PEP-II and KEKB. To raise luminosity: lower  y *, raise I &  y.

SLAC Accelerator Department Early SBF with 3 x E + = 8 GeV E - = 3.5 GeV RF frequency = partial 476 and partial 952. I+ = 5.3 A I- = 12.0 A  y * = 3 mm  x * = 25 cm Emittance = 42 nm Bunch length = 3.3 mm Crossing angle = ~15. mrad Beam-beam parameters = 0.11 N = 3450 bunches L = 3 x cm -2 s -1 Site power with linac and campus = ~90 MW.

SLAC Accelerator Department Final SBF with 8.4 x E + = 8 GeV E - = 3.5 GeV RF frequency = 952 MHz I+ = 10.1 A I- = 22.8 A  y * = 2 mm  x * = 15 cm Emittance = 39 nm Bunch length = 2.2 mm Crossing angle = ~15. mrad Beam-beam parameters = 0.11 N = 6900 bunches L = 8.4 x cm -2 s -1 Site power with linac and campus = ~120 MW.

SLAC Accelerator Department Possible Timeline for Super B Program LOI Construction of upgrades to L = 5-7x10 35 Super-B Program CDR Installation R&D, Design, Proposals and Approvals P5 Construction Planned PEP-II Program (June 30, 2003)(End 2006) (PEP-II ultimate) Commission 2012 Super B Operation 2011

SLAC Accelerator Department Simulation: head-on vs finite- crossing Beam-beam limit is ~0.05 for finite-crossing collision from the both simulations. (Not much difference between 11 & 15 mrad) Head-on collision much improves beam-beam parameter. Discrepancy between Weak-Strong and Strong- Strong simulation is a factor of 2 for head-on collisions. Weak-StrongStrong-Strong 11 mrad = half crossing angle [bunch current]

SLAC Accelerator Department Coherent synchrotron radiation Numerical simulations with mesh (T.Agoh and K.Yokoya) –Analytic formula is not reliable due to strong shielding. Loss factor estimation : –No synchrotron oscillation and no interference between bends. –1 V/pC for 6 mm bunch length (LER) –10 V/pC for 3 mm bunch length (LER) ⇔ 30~40 V/pC in the ring Energy change as a function of z/  z KEKB LER/ 2.6A (5120) bunch length dependence chamber height dependence

SLAC Accelerator Department S-KEKB Choice of   x,  x   x =30, 20, 15 cm  x =24, 18, 12 nm Strong-Strong Beam-Beam Simulations by K. Ohmi Our choice Achievable beam-beam parameters depends on   x and  x.

SLAC Accelerator Department Super KEKB machine parameters Beam-beam parameter is obtained from simulations: strong-strong (weak-strong)