Depolarization Effects and Other Aspects

1. Depolarization Effects and Other Aspects Ian Bailey University of Liverpool / Cockcroft Institute

2. heLiCal collaboration L.I. Malysheva 1,2, I.R. Bailey 1,2, D.P. Barber 3,2,1, E. Baynham 6, A. Birch 1,5, T. Bradshaw 6, A. Brummitt 6, S. Carr 6, J.A. Clarke 1,2,5, P. Cooke 1,2, J.B. Dainton 1,2, Y. Ivanyushenkov 6, L.J. Jenner 1,2, A. Lintern 6, O.B. Malyshev 1,5, G.A. Moortgat-Pick 1,4, J. Rochford 6,P. Schmid 3 and D.J. Scott 1,2,51Cockcroft Institute, 2Department of Physics, University of Liverpool, 3DESY, Deutsches Electronen Synchrotron, 4Institute of Particle Physics Phenomenology, University of Durham, 5CCLRC ASTeC Daresbury Laboratory. 6CCLRC Rutherford Appleton Laboratory

3. Talk Overview • Accelerator Physics Issues (GigaZ) on behalf of Gudi Moortgat-Pick • Status of Robust Spin Transport simulations by HeLiCal collaboration and colleagues.

4. mZ= 91.1876+/- 0.0021 GeV Z=2.4952 +/-0.0023 GeV => undulator at 147.5 GeV position?

7. Robust Spin Transport • Developing reliable software tools that allow the machine to be optimised for spin polarisation as well as luminosity. Aiming to carry out full cradle-to-grave simulations. • Currently carrying out simulations of depolarisation effects in damping rings, beam delivery system and during bunch-bunch interactions. • Currently extending simulations to main linac, etc. Energy spectrum and circular polarisation of photons from helical undulator. Trajectories of electrons through helical undulator. Example of SLICKTRACK simulation showing depolariation of electrons in a ring. • Collaborating with • T. Hartin (Oxford) • P. Bambade, C. Rimbault (LAL) • J. Smith (Cornell) • S. Riemann, A. Ushakov (DESY)

9. Depolarisation Processes Both stochastic spin diffusion through photon emission and classical spin precession in inhomogeneous magnetic fields can lead to depolarisation. 1 mrad orbital deflection  30° spin precession at 250GeV. Largest depolarisation effects are expected at the Interaction Points. Photon emission Spin precession

10. Software Tools e+ source Packages in parentheses will be evaluated at a later date.

11. Positron Source Simulations • Polarisation of photon beam • Ongoing SPECTRA simulations (new version from SPRING-8) • Benchmarked against URGENT (F77 code) • Depolarisation of e- beam • Analytic studies • eg Perevedentsev etal “Spin behavior in Helical Undulator.” (1992) • c.f. trajectory simulations • Target spin transfer • GEANT4 (v 8.2) with polarised cross-sections provided by Andreas Schaelicke, DESY (E166 experiment) • Installed and commissioned at University of Liverpool • Capture Optics • Adding Runge-Kutta and Boris-like T-BMT integration routine to ASTRA

12. Bunch-Bunch Simulations During Interaction Before Interaction After Interaction Spread in Polarisation Large Y Before Interaction During Interaction After Interaction Low Q • Opposing bunches depolarise one another at the IP(s). • Studies of different possible ILC beam parameters (see table on right). • Much work ongoing into theoretical uncertainties. CAIN simulatons

13. Bunch-Bunch Simulations (2) • Theoretical work ongoing into • validity of T-BMT equation in strong fields (checked by Gudi) • higher-order QED processes • spin correlations in pair-production processes • validity of equivalent photon approximation (EPA) for incoherent pair production processes Dominant at ILC energies

14. Tony Hartin, Oxford

15. Tony Hartin, Oxford

16. Tony Hartin, Oxford

17. Damping rings • In ideal Damping Ring depolarising effects are expected to be negligible • Enhancement of synchrotron radiation (wigglers) might lead to the depolarisation effects • Twoout of seven reference lattices were selected: OCS 6km (circle)and TESLA 17 km (dogbone) • Two energies: 5.066GeV and 4.8 GeV (close to resonance) • 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

18. OCS Spin Diffusion at 5.066GeV for spins initially at 100 mrad from n0 Spread of the projections of spins on a horizontal plane reaches equilibrium (250) : Longitudinal polarisation can survive DR!!! Direction of polarisation vector depends on time.

19. OCS Spin Diffusion at 4.8 GeV and5.066 GeV for all spins parallel to n0 The loss of polarisation is negligible

20. SLICKTRACK Simulation Summary • Loss of the vertical component of polarisation in DR is insignificant. • Contrary to common belief there is little decoherence of the horizontal components of spin, thus the direction of the horizontal component polarisation vector depend on time at which the kickers are fired • Our results are in excellent agreement with simple analytical model ( see http://www.desy.de/~mpybar/mypapers.html and arXiv:physics/9709025) • Spin rotators before DR required • Loss of polarisation in BDS is negligible confirming earlier work (J.Smith, Cornell) Future plans We will maintain a rolling study to include extra effects as necessary Include non-linear optics (Collaboration with E. Forest) Linac simulations (started)

21. Further Spin Transport Activities • MERLIN development as a cross-check of main results • Non-linear orbital maps interfaced to SLICKTRACK • Modelling sextupoles, octupoles, undulator, etc • Integrated positron source simulations • Rolling study • Beam-beam theoretical uncertainties • Incoherent pair production and EPA, T-BMT validity, etc… • Comparison with GUINEA-PIG • Novel polarisation flipping in positron source • Flipping polarity of source without spin rotators (cost saving) • Polarimetry and polarisation optimisation (University of Lancaster) • Developing techniques to optimise polarisation at the IP • Optimising use of available computing resources at DL, Liverpool and on the GRID