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

4 Vertical waist has to be a function of x: Z=0 for particles at –  x (-  x /2  at low current) Z=  x /  for particles at +  x (  x /2  at low current) Crabbed waist realized with a sextupole in phase with the IP in X and at  /2 in Y 2Sz 2Sx  z x 2Sx/  2Sz*  e- e+ YY 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  x =100  m,  z =100  m:  y (single pass)=4*10 -4 L=2.1*10 27 Colliding with crossing angle=2*25mrad and  x =2.67um,  z =4mm (  z *  =100um,  x /  =104um):  y =4*10 -3 (single pass) L=2.14*10 27 Same geometric luminosity but 10 times more emittance blowup Adding the “Crab-waist”, Zy_waist(x)=x/2  :  y =1.5*10 -3 (single pass) L=2.29* 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  y (3.8 times the no-crossing case) slide from talk of P.Raimondi on June 14 at SLAC

6 Sigx*  m 2.67 Etax mm0.0 Sigy nm12.6 Betx mm9.0 Bety mm0.080 Sigz_IP mm6.0 Sige_IP1.3e-3 Sige_Lum0.9e-3 Emix nm0.8 Emiy nm0.002 Emiz  m 8.0 Cross_angle mrad2*25 Sigz_DR mm6.0 Sige_DR1.3e-3 Np 10e102.3 Nbunches6000 DR_length km3.0 Damping_time msec20 Nturns_betwe_coll1 Collision freq MHz600 L singleturn 1e361.2 L multiturn 1e361.0 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  y decreased to  x /  c, 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 NominalNo crab 20No crab 14No crab Op20 No crab Op14, 150 No crab Op14, 120 No crab Op4 E250 N2e10 Beta_x Beta_Y Sigma_z Emitt_x10 Emitt_y Eff Cross Ang Lum, E Lum, % Delta_E Ngamma Ephot, MW Rms disr beam X’ Rms disr beam Y’ Rms disr  beam X’ Rms disr  beam Y’ Obtained with simulation by Guinea-Pig code by D.Schulte

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11 Conclusion Parameters can be reoptimized for large crossing angle case and even without relying on crab cavity can achieve nominal luminosity and same  E 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