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Depolarisation in the damping ring of ILC

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Depolarisation in the damping ring of ILC Powered By Docstoc
					Depolarisation Effects at the ILC
        Cockcroft Institute
    L I Malysheva, D P Barber, I R
   Bailey, J A Clarke, J B Dainton, G
            A Moortgat-Pick,
                D J Scott
Introduction
   International Linear Collider (ILC)----new life of an
    old idea.
   A high intensity polarised e+ beam is essential for
    realising the total physics potential of the ILC
    (http://www.ippp.dur.ac.uk/~gudrid/source/ to be
    published) in Physical Reports)
   Delivery of the beam polarisation to the interaction
    region must be robust and without loss of intensity
   Reliable software tools are required to optimise the
    machine for polarisation as well as luminosity

2/10/06          The University of Liverpool/Cockcroft Institute   L I Malysheva
     ILC layout (undulator positron source)




                      polarised
e-/(e+) beam Depolarisation? Depolarisation??  ????
   Misalignments, Synchrotron radiation, Spin precession, Resonances,
                        bunch- bunch effects …
    2/10/06           The University of Liverpool/Cockcroft Institute   L I Malysheva
      Spin behaviour in guide fields
  SPIN PRECESSION ( THOMAS-BARGMANN-MICHEL-TELEGDI)
       

      S , where ( E , B,  , v)   spin  ( g  2) orbit
dS
ds                                                  2
 Synchrotron Radiation                    SPIN DIFFUSION

S  1   2   2 n0 (s)   m(s)   lˆ(s)
                  ˆ          ˆ
                                                            P S
                                                                            bunch
dP    1 d          1 d
           
            2  2
                        ( 2   2  )
dt    2 dt         2 dt
       2/10/06            The University of Liverpool/Cockcroft Institute    L I Malysheva
    Damping rings for the ILC

   In ideal Damping Ring depolarising effects are
    expected to be negligible
   Enhancement of synchrotron radiation (wigglers)
    might lead to the depolarisation effects
   Two out of seven reference lattices were selected:
    OCS 6km (circle) and TESLA 17 km (dogbone)




    2/10/06       The University of Liverpool/Cockcroft Institute   L I Malysheva
     DAMPING RING                         STORAGE RING
 damping time (msec)
                                     storage time (hours)
 S –T effect negligible
                                     S –T effect significant
 No equilibrium
  polarisation                        Equilibrium
                                      polarisation
 (evolution of spin                   (depolarisation rate
  distribution over a few             can be “measured” )
  damping times)
 MERLIN and
  SLICKTRACK                         More then 10 different
                                      codes available
                                      (Handbook of Accelerator
                                      Physics and Engineering)
    2/10/06      The University of Liverpool/Cockcroft Institute   L I Malysheva
           Computer Simulation
    Misalignments were introduced
    STEP 1 (SLICK): linearised orbital and spin motion.
    Reference point as well as an energy scan
   STEP 2 (SLICKTRACK): Monte-Carlo simulation of
    the effects of synchrotron radiation, i.e. evolution
    of the spin distribution over a few damping times
    including full 3-D spin motion
   NO significant depolarising effects have been
    detected confirming the earlier works

      2/10/06      The University of Liverpool/Cockcroft Institute   L I Malysheva
       Spin-orbit resonances
      Spin tune on the closed orbit :                          spin   0
       First order resonances:
                                                              spin  k  Qx
                                                               spin  k  Qy

                                                                   spin  k  Qs
OCS ring depolarisation time with misalignments

       2/10/06           The University of Liverpool/Cockcroft Institute   L I Malysheva
                                     OCS Spin Diffusion at 4.8 GeV
Mean square angular deviation from
the equilibrium direction mrad**2




                                                           turns
                                     2/10/06   The University of Liverpool/Cockcroft Institute   L I Malysheva
                                     OCS Spin Diffusion at 5.066GeV for
                                     spins initially at 100 mrad from n0
                                                                      ˆ
Mean square angular deviation from
the equilibrium direction mrad**2




                                                           turns
                                     2/10/06   The University of Liverpool/Cockcroft Institute   L I Malysheva
        Beam Delivery System (BDS)
   Beam transport to the                           11 mrad NLC-style
    Interaction Region via                              Big Bends

    bending and focusing
    magnets.                                                   IR2
   The 2-mrad beam line                                      2 mrad


    selected (spin precession
      3320 )
                                                                          IR1
   SLICKTRACK                                                           20 mrad


   NO noticeable
    depolarisation (even with
                                           Copy from BDS ILC@SLAC presentation
    misalignments)
        2/10/06        The University of Liverpool/Cockcroft Institute             L I Malysheva
        Beam-Beam Interactions
   CAIN bunch-bunch depolarisation:              Theoretical work ongoing
    survey of theoretical uncertainties             into
    complete.
                                                   Validity of T-BMT
   Studies of possible ILC beam                    equation in strong fields
    parameters:
                                                   validity of equivalent
                                                    photon approximation
                                                    (EPA) for incoherent pair
                                                    production processes
                                                   higher-order processes
                                                   macro-particle dynamics



Gudrid Moortgat [g.a.moortgat-pick@durham.ac.uk]

        2/10/06           The University of Liverpool/Cockcroft Institute   L I Malysheva
     Conclusions
   DR: New lattice design + NEW LAYOUT!!
    (under discussion) … we will maintain a
    rolling study to include extra effects as
    necessary
   BDS: Include non-linear optics
   Beam-beam effects: CAIN code will be
    updated and a comparison with code
    GUINEA-PIG
     2/10/06     The University of Liverpool/Cockcroft Institute   L I Malysheva

				
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