SLAC Accelerator Department SuperBFactory John T Seeman Assistant

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 injector needs no changes SBF

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 xy is the beam-beam parameter (~0. 065) Ib is the bunch current (1 to 3 m. A) n is the number of bunches (~1600) by* is the IP lattice optics function (vertical beta) (10 mm) E is the beam energy (3. 1 and 9 Ge. V) Luminosity (1033 cm-2 s-1)

SLAC Accelerator Department Achieving Super B Luminosities Higher Currents: o More rf power, cooling, injector o More HOM heating (more bunches) o Beam instabilities o Electron clouds, fast ions Smaller by*: o Smaller physical/dynamic aperture o Shorter lifetime, more background Shorter sz: o More HOM heating o Coherent synchrotron radiation o Shorter lifetime, more background Higher tune shifts: o Head-on collisions replaced by angled crossing o Degrades maximum tune shift unless crabbing cavities used

SLAC Accelerator Department PEP-II/Ba. Bar Roadmap: Super B-Factory Study • The Roadmap Committee has studied the future of PEP-II and Ba. Bar 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 1035/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 1035) 1. 5 2. 5 7 RF frequency (MHz) 476 952 Site power (MW) 75 85 100 70 100 Crossing angle No Yes Crab cavities No Yes Replace LER Yes Yes Replace HER No Yes Yes Yes Upgradeable No Yes (to 952 MHz) Yes Recommended Yes Detector requirements depend on projecting backgrounds for luminosities that are >20 times larger than at present

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

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 cavities New Arc magnets New IR layout

SLAC Accelerator Department New IR magnet design (Parker)

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

SLAC Accelerator Department Activities towards luminosity upgrade l. Crab crossing may boost the beam-beam parameter up to 0. 2! (Strong-weak simulation) xy K. Ohmi Head-on(crab) ◊ ◊ ◊ (Strong-strong simulation) crossing angle 22 mrad l. Superconducting crab cavities are under development, will be installed in KEKB in 2005. K. Hosoyama, et al

SLAC Accelerator Department Electron Cloud Instability & multipacting

SLAC Accelerator Department LER aluminum vacuum system: limit at 4. 5 A Photon Stop limits 4. 5 A at 3. 1 Ge. V Antechambers Reduce Electron. Cloud-Instability High power photon stops Total LER SR power = 2 MW

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

SLAC Accelerator Department HOM calculations: 476 MHz cavity S. Novokhotski Rbeam = 95. 25 mm Total loss = 0. 538 V/p. C Loss integral above cutoff = 0. 397 V/p. C HOM Power = 203 k. W @ 15. 5 A 476 MHz cavity with a larger beam opening

SLAC Accelerator Department HOM calculations: 952 MHz cavity S. Novokhotski Rbeam = 47. 6 mm Total loss = 0. 748 V/p. C Loss integral above cutoff = 0. 472 V/p. C HOM Power = 121 k. W @ 15. 5 A 952 MHz cavity with a larger beam opening

SLAC Accelerator Department Luminosity-dependent backgrounds PEP-II Head-On IR Layout o SR in bend & quadrupole magnets o Current dependent terms due to residual vacuum o Bhabha scattering at IP

SLAC Accelerator Department Achieving Super B Luminosities Higher Currents: o More rf power, cooling, injector o More HOM heating (more bunches) o Beam instabilities o Electron clouds, fast ions Smaller by*: o Smaller physical/dynamic aperture o Shorter lifetime, more background Shorter sz: o More HOM heating o Coherent synchrotron radiation o Shorter lifetime, more background Higher tune shifts: o Head-on collisions replaced by angled crossing o Degrades maximum tune shift unless crabbing cavities used

SLAC Accelerator Department Power Scaling Equations • • • Synch rad ~ I E 4/r Resistive wall ~ I 2 total/r 1/frf/sz 3/2 Cavity HOM ~ I 2 total/frf/sz 1/2 Cavity wall power = 50 k. W Klystron gives 0. 5 MW to each cavity Magnet power ~ gap~r 1

SLAC Accelerator Department Power scaling equations • Synch rad ~ I E 4/r • Resistive wall ~ I 2 total/r 1/frf/sz 3/2 • Cavity HOM ~ I 2 total/frf/sz 1/2 • Cavity wall power = 50 k. W • Klystron gives 0. 5 MW to each cavity • Magnet power ~ gap ~r

SLAC Accelerator Department Site power limits 476 MHz 34 2. 5 x 10 34 1. 5 x 10 7 x 1034 952 MHz (Linac, PEP-II magnets and campus power = 40 MW)

SLAC Accelerator Department Recommended scenario: 5 to 7 x 1035 • Replace present RF with 952 MHz frequency over period of time. • Use 8 x 3. 5 Ge. V 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 0. 6 -0. 8 nsec spacing. ) • Push by* 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 1035; with thin pixels beyond – Headroom for machine up to 8. 5 x 1035; requires additional rf, which can be staged into machine over time

SLAC Accelerator Department Luminosity Equation • When vertical beam-beam parameter is limited. • xy ~ 0. 06 in PEP-II and KEKB. • To raise luminosity: lower by*, raise I & xy.

SLAC Accelerator Department Early SBF with 3 x 1035 • • • • E+ = 8 Ge. V E- = 3. 5 Ge. V RF frequency = partial 476 and partial 952. I+ = 5. 3 A I- = 12. 0 A by* = 3 mm bx* = 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 1035 cm-2 s-1 Site power with linac and campus = ~90 MW.

SLAC Accelerator Department Final SBF with 8. 4 x 1035 • • • • E+ = 8 Ge. V E- = 3. 5 Ge. V RF frequency = 952 MHz I+ = 10. 1 A I- = 22. 8 A by* = 2 mm bx* = 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 1035 cm-2 s-1 Site power with linac and campus = ~120 MW.

SLAC Accelerator Department Possible Timeline for Super B Program Super-B Program 2001 Construction of upgrades to L = 5 -7 x 1035 R&D, Design, Proposals and Approvals 2003 2005 2006 2008 Super B Operation 2010 2011 2012 Construction LOI CDR Installation Commission P 5 Planned PEP-II Program (June 30, 2003) (End 2006) (PEP-II ultimate)

SLAC Accelerator Department Simulation: head-on vs finitecrossing Weak-Strong 11 mrad = half crossing angle [bunch current] Strong-Strong [bunch current] • 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.

SLAC Accelerator Department Coherent synchrotron radiation Energy change as a function of z/sz KEKB LER/ 2. 6 A (5120) bunch length dependence • 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/p. C for 6 mm bunch length (LER) – 10 V/p. C for 3 mm bunch length (LER) ⇔ 30~40 V/p. C in the ring chamber height dependence

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

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