WP2.3 - Robust Spin Polarisation Status Ian Bailey, University of Liverpool on behalf of Helical Collaboration I.R. Bailey, P. Cooke, J.B. Dainton, L.J. Jenner, L.I. Malysheva (University of Liverpool / Cockcroft Institute) D.P. Barber (DESY / Cockcroft Institute) P. Schmid (DESY) G.A. Moortgat-Pick (IPPP, University of Durham / Cockcroft Institute) A. Birch, J.A. Clarke, O.B. Malyshev, D.J. Scott (CCLRC ASTeC Daresbury Laboratory / Cockcroft Institute) E. Baynham, T. Bradshaw, A. Brummit, S. Carr, Y. Ivanyushenkov, A. Lintern, J. Rochford (CCLRC Rutherford Appleton Laboratory) LC-ABD: WP2.3 (robust spin polarisation) and WP5.1 (helical undulator). EUROTeV: WP3 (damping rings) and WP4 (polarised positron source). WP2.3 Aims and Overview • Developing reliable software tools that Summary of major milestones allow the machine to be optimised for achieved to date: high polarisation as well as luminosity. •Updated SLICKTRACK software • Currently carrying out simulations of package to include full non- depolarisation effects in damping rings, commuting spin rotations beam delivery system, main linac and during bunch-bunch interactions. •Simulated spin dynamics in ILC • Developing simulations of spin •damping rings transport through the positron source. •beam delivery system •We require relative uncertainty on polarisation to be less than 0.1% at IP •main linac for precision physics. •Evaluated theoretical •Luminosity-weighted polarisation uncertainties in beam-beam cannot be directly measured with a interactions at the ILC polarimeter. •Implemented first polarised Collaborating with incoherent pair-production T. Hartin (Oxford) processes in CAIN. P. Bambade, C. Rimbault (LAL) J. Smith (Cornell) S. Riemann, A. Ushakov (DESY) Depolarisation Processes Both stochastic spin diffusion through photon emission and classical spin precession in inhomogeneous magnetic fields can lead to depolarisation. ( g 2) spin orbit Photon emission 2 1 mrad orbital deflection 30° spin precession at 250GeV. Largest depolarisation effects are expected at the Interaction Points. Spin precession Software Tools Undulator Collimator / Target Capture Optics Physics e+ source Electrodynamics Standard Model T-BMT Process (spin spread) Packages SPECTRA, GEANT4, FLUKA ASTRA URGENT Damping ring Main Linac / Interaction BDS Region Physics T-BMT T-BMT Bunch-Bunch Process (spin diffusion) Packages SLICKTRACK, SLICKTRACK CAIN2.35 (Merlin) (Merlin) (Guinea-Pig) Packages in parentheses will be evaluated at a later date. Beam-Beam Simulations Theoretical work ongoing into: •Require ΔP/P < 0.1% at IP •Compare with CAIN simulations •validity of anomalous moment of depolarisation at IP (below) expression used to implement T- BMT equation in strong fields (now validated by Gudi!) •higher-order QED processes (eg second-order incoherent Breit- Wheeler - ICBW) •spin correlations in pair- production processes •In addtion - the estimated •validity of equivalent photon theoretical uncertainty in approximation (EPA) for incoherent pair production luminosity is ~1% at ILC processes energies (eg not valid for Bremstrahlung!) Beam-Beam Simulations(2) Incoherent pair-production Polarised cross-sections for dominates at ILC energies incoherent Breit-Wheeler pair production added to CAIN: •Equivalent Photon Approximation Tony Hartin requires proper treatment of initial Beamstrahlung photons have little circular and final state polarisation. polarisation final state e+ /e- are largely •Not currently included in CAIN unpolarised. SLICKTRACK Simulations Damping Rings Beam Delivery System Simulations show negligible • Simulated 2-mrad beam line depolarisation of vertically- • Spin precession ~332° aligned spins - even when • Loss of polarisation ~0.06% injection energy is close to spin resonances. • Cross-checked with BMAD • (J. Smith, Cornell - ILC-NOTE-2007-012) Behaviour of horizontal component of spins more complex (eg misaligned spin 11 mrad NLC-style rotators) Big Bends In general, horizontal component does NOT fully IR2 2 mrad decohere Effect of very large positron source energy spread (+/- IR1 25MeV) on horizontal 20 mrad component being investigated. SLICKTRACK Simulations (2) Main Linac •SLICKTRACK has been updated to include acceleration and ‘linear mode’ •Expect spin precession ~26° for 11km Earth-following linac (250GeV) •First results (w/o misalignments) show negligible depolarisation •Inconsistent with BMAD result? •I.e. polarisation reduced by factor •Further investigation needed. ~cos(10-4 radians) d WP2.3 - Remaining Milestones and Future Plans The motivation for a complete cradle to grave spin tracking simulation has grown as the high energy physics community has increasingly identified the importance of polarised beams as a means to offset any reduction in ILC luminosity. This work has been identified as high priority by the Global R&D board. We have simulated most of the machine but not yet in a fully integrated fashion. We need (LC-ABD2, etc): Further development of SLICKTRACK for full non-linear orbital motion study of BDS and study of main linac (collaborating with E. Forest and Kai Hock) Development of positron source simulation including effects such as beam jitter and the investigation of spin flip techniques. Further theoretical work on beam-beam interactions (beamstrahlung models, higher-order QCD, etc) A continued rolling study of the whole machine to allow optimum use of polarisation as a tool for the ILC. Benchmarking from BMAD, Merlin, etc.
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