Progress Update on the Electron Polarization Study in the JLEIC Fanglei Lin JLEIC R&D Meeting, March 2, 2017 F. Lin

Current Status and Working Plan Electron polarization lifetime at 5 GeV was calculated using analytical code SLICK and Monte-Carlo simulation code SLICKTRACK, for the baseline JLEIC electron collider ring design. Polarization lifetimes at other energies are simply scaled at this moment, should and will be verified once the lattice design is finalized. Spin tune scans with quadrupole vertical misalignment and dipole role were performed at 5GeV JLEIC electron collider ring. Simulation shows no synchrotron sideband resonances in the figure-8 shape electron collider ring. Spin-orbit depolarization time reduces by a factor of 2.6 in the reduced-emittance ring optics (30% emittance reduction coming from optimization of matching and spin rotator sections in the baseline design using PEP-II magnets). Working on spin tracking using ZGOUBI for benchmarking. Working Plan: Continue spin tracking using ZGOUBI Study the beam-beam effect on the polarization Study the crab crossing effect on the polarization Develop spin matching to extend the polarization lifetime See Vasiliy’s talk about collaboration with A. Kondratenko’s team

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Spin Tune Scan SLICK/SLICKTRACK allows one to insert a zero length spin tuning magnet to move the spin tune away from zero. Such magnet in the code only rotates the spin, leaving the orbit intact. Longitudinal field spin tuning solenoid in one straight where the polarization is longitudinal Only moves the spin tune away from zero Does not change the spin direction Breaks the current spin matching condition in the straight IP Spin Rotator e- Magnetic field Polarization Spin tuning solenoid

Spin Tune Scan @ 5 GeV Quadrupole vertical misalignment with a rms value of 0.2mm and dipole role with a rms value of 0.2 mrad. The orbit is corrected with correctors around the ring. First order spin resonance occurs when 500 electrons in the Monte-Carlo simulation Optimum Spin Tune 0.0267 Nasty, nasty sidebands ! Figure-8 MEIC collider ring has no synchrotron sideband resonances !

Baseline Electron Ring Circumference of 2154.28 m = 2 x 754.84 m arcs + 2 x 322.3 straights Chromaticities: (H,V) = (-149, -123) Figure-8 crossing angle 81.7 Electron collider ring w/ major machine components e- R=155m RF Spin rotator CCB Arc, 261.7 81.7 Forward e- detection IP Tune trombone & Straight FODOs Future 2nd IP Regular arc FODO cell Spin rotator Matching section Dipole set 2nd sol. + decoupling quads 1st sol. + decoupling quads

Reduced-Emittance Electron Ring Circumference of 2185.55 m = 2 x 811.84 m arcs + 2 x 280.92 straights Chromaticities: (H,V) = (-138, -119) Figure-8 crossing angle 81.7 Regular arc FODO cell Spin rotator Dipole set 2nd sol. + decoupling quads 1st sol. + decoupling quads

Spin Tune Scan @ 5 GeV Quadrupole vertical misalignment with a rms value of 0.2mm and dipole role with a rms value of 0.2 mrad. The orbit is corrected with correctors around the ring. First order spin resonance occurs when 500 electrons in the Monte-Carlo simulation Optimum Spin Tune 0.0267 Optimum Spin Tune 0.0249 Spin-orbit depolarization time reduces by a factor of 2.6 in the reduced-emittance ring optics

Solenoid Strength Spin tuning solenoid strengths in spin tune scans Optimum Spin Tune 0.0267 For the optimum spin tune of 0.0267 where the polarization lifetime reaches 8 hours, the required integral of spin tuning solenoid field is ~3 Tm. The stronger the solenoid field is, the larger the spin tune is. But the strong solenoid field breaks the spin matching badly and leaves a short polarization lifetime.