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Possibilities of ILC parameters optimization with crossing angle

Possibilities of ILC parameters optimization with crossing angle. SLAC, June 27, 2006. P. Raimondi, M.Pivi, A.Seryi. Outline.

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Possibilities of ILC parameters optimization with crossing angle

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  1. Possibilities of ILC parameters optimization with crossing angle SLAC, June 27, 2006 P. Raimondi, M.Pivi, A.Seryi

  2. Outline • Inspired by new parameter set suggested by P.Raimondi for Super-B factory, where crossing angle, combined with crabbed waist allow to focus beam to very small size and reduce beam-beam induced emittance growth to 1E-3 per collision, resulting in luminosity of ~1E36 • Reoptimization of ILC parameters for crossing angle case seem to be possible, and about the same luminosity can be achieved even without crab cavity compensation

  3. Crossing angle concepts Overlapping region Both cases have the same luminosity, (2) has longer bunch and smaller sx With large crossing angle X and Z quantities are swapped: Very important!!! Sx Sz 1) Standard short bunches Overlapping region Sz Sx 2) Crossing angle slide from talk of P.Raimondi on June 14 at SLAC

  4. x bY e- e+ 2Sx/q Vertical waist has to be a function of x: Z=0 for particles at –sx(- sx/2q at low current) Z= sx/q for particles at + sx(sx/2q at low current) Crabbed waist realized with a sextupole in phase with the IP in X and at p/2 in Y q 2Sz*q z 2Sz 2Sx Crabbed waist removes bb betratron coupling Introduced by the crossing angle slide from talk of P.Raimondi on June 14 at SLAC

  5. Emittance blowup due to the crossing angle Colliding with no crossing angle and sx=100mm, sz=100mm: Dey (single pass)=4*10-4 L=2.1*1027 Colliding with crossing angle=2*25mrad and sx=2.67um, sz=4mm (sz*q=100um, sx/q=104um): Dey =4*10-3 (single pass) L=2.14*1027 Same geometric luminosity but 10 times more emittance blowup Adding the “Crab-waist”, Zy_waist(x)=x/2q: Dey =1.5*10-3 (single pass) L=2.29*1027 - the ‘hour glass’ is reduced, the geometric luminosity is higher: small effect about 5% more luminosity - the main effect: blowup due the the beam-beam is reduced, about a factor 2.4 less Dey (3.8 times the no-crossing case) slide from talk of P.Raimondi on June 14 at SLAC

  6. Defined a parameters set for Super-B based on ILC-like parameters • Same DR emittances • Same DR bunch length • Same DR bunch charges • Same DR damping time • Same ILC-IP betas • Crossing Angle and Crab Waist to minimize BB blowup slide from talk of P.Raimondi on June 14 at SLAC

  7. Parameter scaling • In ILC with crossing angle compensated • In ILC with crossing angle, all *

  8. Ultimate L with crossing angle • Achieved when by decreased to sx/qc, then one can show that L does not depend on crossing angle and given by the same formula • So, in principle, same luminosity can be achieved with crossing angle if one can focus the beam tighter (with proper stability etc)

  9. Example of ILC parameters with crossing angle Obtained with simulation by Guinea-Pig code by D.Schulte

  10. Conclusion • Parameters can be reoptimized for large crossing angle case and even without relying on crab cavity can achieve nominal luminosity and same dE • Reoptimized parameters require tighter focusing in Y (beam size smaller, stability may need to be tighter, etc) • Increased betaX is better from collimation depth point of view

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