Effect of high synchrotron tune on Beam- Beam interaction: simulation and experiment A.Temnykh for CESR operating group Cornell University, Ithaca, NY USA SBSR05, Nov , Frascati, Italy

SBRS05 Nov , Frascati, Italy 2 Content CESR-c scheme and example of operation High synchrotron tune and effect of phase modulation between collisions. Single and multi-particle tracking results Experimental Beam- Beam interaction study Low wigglers field / reduced bunch length Reduced Fs Conclusion

SBRS05 Nov , Frascati, Italy 3 CESR-c scheme of operation Single ring e+/e- collider Multi-bunch operation, 40 bunches grouped in 8 trains Beam separation in parasitic crossing is provided by horizontal orbit distortion with electrostatic plates. Pretzel scheme. Maximum separation in parasitic crossing. Limit due to beam pipe dimension.

SBRS05 Nov , Frascati, Italy 4 CESR-c operation example Max Luminosity: ~ 6.2x /cm 2 /sec, 1.5 x /cm 2 /sec per bunch. Max Current per bunch ~ 2.0mA. Max beam-beam perameters:  y (+) ~ 0.035,  y (-) ~ 0.019, ~  x (+) ~ 0.025,  x (-) ~ 0.03, ~ e+ beam current is limited by long range beam-beam interaction. xx yy yy

SBRS05 Nov , Frascati, Italy 5 Synchrotron tune and phase modulation Description: For CESR-c  z /    similar to other machines) But s ~ 0.1 !!! ( KEKb ~ 0.022, PEP-II ~ 0.029/0.041, ~ 0.05, DAFNE ~ 0.003, DORIS ~ 0.005?, VEPP- 4 ~ 0.012)

SBRS05 Nov , Frascati, Italy 6 Single particle tracking BBI with round beam with turn-to-turn phase modulation:  0.033,  a s =1. Tune scan from 220kHz (Q = 0.564) to 245kHz (Q = 0.628) fs = 39kHz ( s = 0.10) fs = 19.5kHz ( s = 0.050) fs = 0 5/8 6/10 7/12 8/14 (1+2 s )/2 (1+3 s )/2 (1+4 s )/2

SBRS05 Nov , Frascati, Italy 7 Phase modulation effect: Multi-particles tracking (D. Rubin)

SBRS05 Nov , Frascati, Italy 8 How can we change in machine ? 1)Reduce  z keeping constant s and  y Wiggler field reduction from 2.1T to 1.4T gives  E and  z reduction by a factor (2.1/1.4) 1/2 ~ 1.21 Side effect: damping time change by a factor (2.1/1.4) 2 ~ 2.25 Experimental study (1.4T wiggler field optics)

SBRS05 Nov , Frascati, Italy 9 Experimental study (prediction for 1.4T wiggler field) Luminosity simulation: 1.4T, sig_z = 10.3mm 2.1T, sig_z ~ 12.3mm 1.4 T, L ~ 2.2x10 30 at 2mA 2.1T, L ~ 2.0x1030 at 2mA

SBRS05 Nov , Frascati, Italy 10 Experimental study (1.4T wiggler field optics) Limits: Current per bunch ~ 1.75mA Luminosity per bunch ~ 0.9 x /cm 2 /sec Limits due to beam-beam interaction at IP. First vertical beam size growing, then beam life time decreasing.  x ~ 0.030,  y ~ Conclusion: Probably in this optics luminosity can be not worse than in reference, but because of lack of damping injection was slower.

SBRS05 Nov , Frascati, Italy 11 What can we can do more with ? 2) Reduce s keeping constant  z /  y In this way we can increase  y, but not luminosity. Experimental study (low fs experiment)

SBRS05 Nov , Frascati, Italy 12 Experimental study (low fs experiment) Colliding & non-colliding beam spectrum Interesting moment:

SBRS05 Nov , Frascati, Italy x0.8mA collision  x ~  y ~ x2.0mA collision  x ~  y ~ x3.0mA collision  x ~  y ~ Experimental study (low fs experiment) High fs optics: fs = 39kHz  s =0.100)   y =12.7mm,  l =12mm, d = s  l/  y = Low fs optics: fs = 18kHz,  s =0.046)   y =21.5mm,  l =26mm, d = x2.0mA collision  x ~  y ~ x3.0mA collision  x ~  y ~ With lower fs we have reached higher  y !!! One can see  y saturation, i.e., L/I is not growing.

SBRS05 Nov , Frascati, Italy 14 Conclusion Have experimented with: 1.Reduced bunch length /low (1.4T) wiggler field 2.Low fs Experiment 1), probably, and 2), definitely, indicated that vertical betatron phase modulation between collisions resulted from high fs has negative impact on CESR-c beam- beam performance. Simulation results are in agreement with experiments.

SBRS05 Nov , Frascati, Italy 15 Appendix: Tune plane exploration: “high” and “low” tune region maps. Low tune region: 200 < fh < 220 kHz (0.513 < Qx < 0.564) 230 < fv < 250 kHz (0.590 < Qy < 0.641) High tune region: 212 < fh < 237 kHz (0.544 < Qx < 0.608) 247 < fv < 272 kHz (0.633 < Qy < 0.697) 2fh – fs = f0 fh – fv + fs = f0 6fv = 4f0 6fv – 2fs = 4f0

SBRS05 Nov , Frascati, Italy 16 2fh – fs = f0 fh + fs – fv = f0 Appendix: Tune plane exploration: “low” tune region: < Qx < 0.564; < Qy < x 1 head-on collision, weak-strong beam-beam interaction. Tune scan with vertical beam size measurement of the weak (positron) beam. CESR-c working point: fh=205kHz (Qh=0.526), fv = 235kHz (Qv=0.603) No beam – beam interaction Seen “machine” resonances 1)2fh – fs = f0 2)fh – fv + fs = f0 “Mild” beam – beam interaction Resonance 2fh – fs = f0 becomes stronger and moves toward working point. “ Strong” beam – beam interaction. Resonance 2fh – fs = f0 hits working point.

SBRS05 Nov , Frascati, Italy 17 Appendix: Tune plane exploration: “High” tune region: < Qx < 0.564; < Qy < No beam – beam interaction. Seen “machine” resonance 1)fh – fv + fs = f0 “Mild” beam – beam interaction Seen “beam-beam” resonances 6fv = 4f0 and 6fv - 2fs = 4f0. “ Strong” beam – beam interaction. Effects of 6fv = 4f0 and 6fv - 2fs = 4f0 spread downward. No good place for working point. 1 x 1 head-on collision, weak-strong beam-beam interaction. Tune scan with vertical beam size measurement of the weak (positron) beam. fh – fv + fs = f0 6fv = 4f0 6fv - 2fs = 4f0 6fv = 4f0

SBRS05 Nov , Frascati, Italy 18 Appendix: Tune plane exploration: Conclusion In the “high” tune region beam- beam performance limited by beam- beam interaction driven resonances. We can not eliminate them. In the “low” tune region “machine” driven resonances affect the beam- beam performance. We can damp them.