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					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
xy is the beam-beam parameter (~0.065)
Ib is the bunch current (1 to 3 mA)
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 GeV)
Luminosity (1033 cm-2 s-1)



                                  nx y EIb
          L  2.17 x10       34

                                    by
                                     *
       SLAC Accelerator Department


       Achieving Super B Luminosities
                                                                        nx y EI b
nI b     Higher Currents:                              L  2.17  10
                                                                   34

                                                                          by
                                                                           *
              o More rf power, cooling, injector
              o More HOM heating (more bunches)
              o Beam instabilities
              o Electron clouds, fast ions
by
 *
         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
xy        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/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 1035/cm2/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       57
RF frequency                                            47695
                      476             476        952
(MHz)                                                      2
Site power
(MW)
                       75              85        100    70100
Crossing angle        No               Yes       Yes      Yes
Crab cavities         No               Yes       Yes      Yes
Replace LER           Yes              Yes       Yes      Yes
Replace HER           No               Yes       Yes      Yes
                                        Yes            Recommended
Upgradeable           No
                                   (to 952MHz)
                                                 Yes      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 Arc magnets
•




                                               PEP-II 10 36 B-Factory +/- 12 mrad xing angle Q2 septum at 2.5 m
                                      30

                                                   Q5                                  Q2
                                                                                                         e+
                                                            Q4
                                      20


                                                                                  Q1
                                      10                                 Q1
                                              e-

                                    cm 0



                                     -10                                          Q1
                                                                         Q1


                                     -20                                                      Q4
                                                                                                         Q5
                                                                   Q2

                                     -30
                                       -7.5         -5           -2.5         0         2.5          5            7.5
                                                                                                              31-JAN-2002
                                                                              m                               M. Sullivan




          New RF cavities                                               New IR layout
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
Crab crossing may boost the beam-beam parameter up to 0.2!
                                        (Strong-weak simulation)                                                                                   K. Ohmi

      xy
                                                                                                                Head-on(crab)
                                                                                          ◊                     (Strong-strong simulation)
                                                                               ◊               ◊
                                                                         ◊                                     crossing angle 22 mrad
                                                          ◊




 Superconducting crab cavities are
 under development, will be installed
 in KEKB in 2005.
              Input Coupler
                                    I.R. 90
                    I.D. 120
   I.D. 240

                                                                    I.D. 188
                                                                                                   I.R.241.5



                                                       Coaxial Coupler
                                                                                         866
                                    I.R. 20

                    I.D. 30
                Monitor Port




       0                       50                           100                    150
                                                                                               483

                                          scale (cm)                                                                                         K. Hosoyama, et al
 SLAC Accelerator Department


Electron Cloud Instability & multipacting
             SLAC Accelerator Department


           LER aluminum vacuum system: limit at 4.5A
  Photon Stop
     limits
4.5 A at 3.1 GeV


  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              Ante-chamber
                                          with solenoid field
  radiation.
• Reduce effects of electron
  clouds.
SLAC Accelerator Department

       HOM calculations: 476 MHz
                cavity           S.Novokhotski



                                    Rbeam = 95.25 mm
                                Total loss = 0.538 V/pC
                              Loss integral above cutoff =
                                       0.397 V/pC
                                HOM Power = 203 kW
                                        @ 15.5A




   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/pC
                              Loss integral above cutoff =
                                       0.472 V/pC
                                HOM Power = 121 kW
                                        @ 15.5A




   952 MHz cavity with a
    larger beam opening
             SLAC Accelerator Department


               Luminosity-dependent backgrounds
                            HER Radiative Bhabhas
                    30
                                                                                        2.5              3
                                                                                                                        3.5

                                                                                                         eV             4
                                                                                                     G
                    20                                                                           1
                                                                                              3.
    PEP-II                                                         1
                                                                       1.5 2

  Head-On IR                                                 0.5

    Layout          10
                                                                                                                        6
o SR in bend & cm        9 GeV
                                                                                 4.5                                    6.5
                                                                                5 5.5                                   7
  quadrupole         0
                                                                                                                         8
                                                                                                                           7.5

  magnets
                                                                                                 9 GeV
o Current
                   -10
  dependent
  terms due to
  residual vacuum -20                   eV
o Bhabha                     3.
                                1
                                    G

  scattering at IP
                    -30
                      -7.5                   -5   -2.5   0                2.5           5      M. Sullivan
                                                                                                                7.5
                                                                                               Feb. 8, 2004

                                                         m                                     API88k3_R5_RADBHA_TOT_7_5M
       SLAC Accelerator Department


       Achieving Super B Luminosities
                                                                        nx y EI b
nI b     Higher Currents:                              L  2.17  10
                                                                   34

                                                                          by
                                                                           *
              o More rf power, cooling, injector
              o More HOM heating (more bunches)
              o Beam instabilities
              o Electron clouds, fast ions
by
 *
         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
xy        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 E4/r
•   Resistive wall ~ I2total/r1/frf/sz3/2
•   Cavity HOM ~ I2total/frf/sz1/2
•   Cavity wall power = 50 kW
•   Klystron gives 0.5 MW to each cavity
•   Magnet power ~ gap~r1
    SLAC Accelerator Department


             Power scaling equations
• Synch rad ~ I E4/r
• Resistive wall ~
  I2total/r1/frf/sz3/2
• Cavity HOM ~
  I2total/frf/sz1/2
• Cavity wall power =
  50 kW
• Klystron gives 0.5
  MW to each cavity
• Magnet power ~ gap
  ~r
SLAC Accelerator Department


                Site power limits




                  476 MHz

            2.5x1034            7x1034
        1.5x1034
                                         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 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 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.




                r0 Nb b y 
                         *

     x 
       
                                    ( flatbeams)
             2 s s   *     *
       y
                        y      x


                             nx y EIb
      L  2.17 x10      34

                                by
                                 *
      SLAC Accelerator Department


                  Early SBF with 3 x 1035
•   E+ = 8 GeV
•   E- = 3.5 GeV
•   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-2s-1
•   Site power with linac and campus = ~90 MW.
      SLAC Accelerator Department


                Final SBF with 8.4 x 1035
•   E+ = 8 GeV
•   E- = 3.5 GeV
•   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-2s-1
•   Site power with linac and campus = ~120 MW.
             SLAC Accelerator Department


           Possible Timeline for Super B Program
   Super-B            R&D, Design,                      Construction of              Super B
   Program            Proposals and                      upgrades to                Operation
                        Approvals                        L = 5-7x1035

                                                                               Ldt ~ 10 ab-1/yr

2001    2003               2005 2006             2008          2010 2011 2012

                                                 Construction
                                                               Installation
                            LOI     CDR
                                     P5                                             Commission

Planned PEP-II Program

         Ldt  140 fb
                      -1
                               Ldt  500 fb-1                   Ldt ~ 1  2 ab-1
         (June 30, 2003)          (End 2006)                    (PEP-II ultimate)
       SLAC Accelerator Department

                 Simulation: head-on vs finite-
                           crossing
                     Weak-Strong             Strong-Strong




11 mrad = half                [bunch               [bunch
crossing angle                current]             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/ 2.6A (5120)
                                bunch length                                  chamber height
                                dependence                                    dependence




• Numerical simulations with mesh (T.Agoh and K.Yokoya)
   – Analytic formula is not reliable due to strong shielding.     c  h 3 r  2.5 mm

• 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
     SLAC Accelerator Department


           S-KEKB Choice of b*x, ex
• b*x=30, 20, 15 cm                Strong-Strong Beam-Beam
                                   Simulations by K. Ohmi
• ex=24, 18, 12 nm




                                                   Our choice


  Achievable beam-beam parameters depends on b*x and ex.
              SLAC Accelerator Department


             Super KEKB machine parameters
             Parameter                        LER                     HER                Unit
Beam currrent                     I           9.4                     4.1                    A
Number of bunches                nb                        5018
Horizontal beta at IP            bx                         20                               cm
Vertical beta at IP              by                      3                              mm
Bunch length                     sz                      3                              mm
Emittance                        ex                     24                               nm
Coupling                                              0.75                               %
Crossing angle                   x            30 (crab-crossing)                       mrad
                                                     -4                      -4
Momentum compaction              p         2.7x10                  1.8x10
RF voltage                       Vc            15                      20                    MV
Synchrotron tune                 s          0.031                   0.019
Vertical beam-beam               xy                  0.14 (0.28)
                                                                                        35
Luminosity                       L                        2.5 (5)                 x10        cm -2 s-1

                      Beam-beam parameter is obtained from
                      simulations: strong-strong (weak-strong)

				
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