1. Effect of high synchrotron tune on Beam- Beam interaction: simulation and experiment A.Temnykh for CESR operating group Cornell University, Ithaca, NY 14850 USA SBSR05, Nov 7-8 2005, Frascati, Italy

2. SBRS05 Nov 7 - 8 2005, 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

3. SBRS05 Nov 7 - 8 2005, 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.

4. SBRS05 Nov 7 - 8 2005, Frascati, Italy 4 CESR-c operation example Max Luminosity: ~ 6.2x10 31 1/cm 2 /sec, 1.5 x 10 30 1/cm 2 /sec per bunch. Max Current per bunch ~ 2.0mA. Max beam-beam perameters:  y (+) ~ 0.035,  y (-) ~ 0.019, ~ 0.026  x (+) ~ 0.025,  x (-) ~ 0.03, ~ 0.027 e+ beam current is limited by long range beam-beam interaction. xx yy yy

5. SBRS05 Nov 7 - 8 2005, 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, CESR @5.5GeV ~ 0.05, DAFNE ~ 0.003, DORIS ~ 0.005?, VEPP- 4 ~ 0.012)

6. SBRS05 Nov 7 - 8 2005, 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

7. SBRS05 Nov 7 - 8 2005, Frascati, Italy 7 Phase modulation effect: Multi-particles tracking (D. Rubin)

8. SBRS05 Nov 7 - 8 2005, 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)

9. SBRS05 Nov 7 - 8 2005, 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

10. SBRS05 Nov 7 - 8 2005, Frascati, Italy 10 Experimental study (1.4T wiggler field optics) Limits: Current per bunch ~ 1.75mA Luminosity per bunch ~ 0.9 x 10 29 1/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 ~ 0.020 Conclusion: Probably in this optics luminosity can be not worse than in reference, but because of lack of damping injection was slower.

11. SBRS05 Nov 7 - 8 2005, 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)

12. SBRS05 Nov 7 - 8 2005, Frascati, Italy 12 Experimental study (low fs experiment) Colliding & non-colliding beam spectrum Interesting moment:

13. SBRS05 Nov 7 - 8 2005, Frascati, Italy 13 0.8x0.8mA collision  x ~ 0.015  y ~ 0.020 2.0x2.0mA collision  x ~ 0.026  y ~ 0.025 3.0x3.0mA collision  x ~ 0.041  y ~ 0.025 Experimental study (low fs experiment) High fs optics: fs = 39kHz  s =0.100)   y =12.7mm,  l =12mm, d = s  l/  y =0.0944 Low fs optics: fs = 18kHz,  s =0.046)   y =21.5mm,  l =26mm, d = 0.0558 2.0x2.0mA collision  x ~ 0.041  y ~ 0.030 3.0x3.0mA collision  x ~ 0.049  y ~ 0.033 With lower fs we have reached higher  y !!! One can see  y saturation, i.e., L/I is not growing.

14. SBRS05 Nov 7 - 8 2005, 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.

15. SBRS05 Nov 7 - 8 2005, 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

16. SBRS05 Nov 7 - 8 2005, Frascati, Italy 16 2fh – fs = f0 fh + fs – fv = f0 Appendix: Tune plane exploration: “low” tune region: 0.513 < Qx < 0.564; 0.590 < Qy < 0.641 1 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.

17. SBRS05 Nov 7 - 8 2005, Frascati, Italy 17 Appendix: Tune plane exploration: “High” tune region: 0.513 < Qx < 0.564; 0.590 < Qy < 0.641 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

18. SBRS05 Nov 7 - 8 2005, 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.