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Effect of high synchrotron tune on Beam-Beam interaction: simulation and experiment

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

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Effect of high synchrotron tune on Beam-Beam interaction: simulation and experiment

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  1. Effect of high synchrotron tune on Beam-Beam interaction: simulation and experiment Temnykh for CESR operating group Cornell University, Ithaca, NY 14850 USA SBSR05, 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 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. SBRS05 Nov 7 - 8 2005, Frascati, Italy

  4. CESR-c operation example sy xy xx • Max Luminosity: ~ 6.2x1031 1/cm2/sec, 1.5 x 1030 1/cm2/secper bunch. • Max Current per bunch ~ 2.0mA. • Max beam-beam perameters: • xy(+) ~ 0.035, xy(-) ~ 0.019, <xy> ~ 0.026 • xx(+) ~ 0.025, xx(-) ~ 0.03, <xx> ~ 0.027 • e+ beam current is limited by long range beam-beam interaction. SBRS05 Nov 7 - 8 2005, Frascati, Italy

  5. Synchrotron tune and phase modulation Description: For CESR-c sz/b* ~ 1 ( similar to other machines) But ns~ 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) SBRS05 Nov 7 - 8 2005, Frascati, Italy

  6. Single particle tracking BBI with round beam with turn-to-turn phase modulation: x = 0.033, s/b = 1, as=1. Tune scan from 220kHz (Q = 0.564) to 245kHz (Q = 0.628) fs = 0 fs = 39kHz (ns= 0.10) fs = 19.5kHz (ns= 0.050) 8/14 6/10 5/8 (1+4ns)/2 7/12 (1+2ns)/2 (1+3ns)/2 SBRS05 Nov 7 - 8 2005, Frascati, Italy

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

  8. Experimental study(1.4T wiggler field optics) • How can we change in machine ? • Reduce sz keeping constant ns and by • Wiggler field reduction from 2.1T to 1.4T gives sE and sz 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 SBRS05 Nov 7 - 8 2005, Frascati, Italy

  9. Experimental study (prediction for 1.4T wiggler field) Luminosity simulation: 2.1T, sig_z ~ 12.3mm 1.4T, sig_z = 10.3mm 1.4 T, L ~ 2.2x1030 at 2mA 2.1T, L ~ 2.0x1030 at 2mA 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 1029 1/cm2/sec • Limits due to beam-beam interaction at IP. First vertical beam size growing, then beam life time decreasing. • xx ~ 0.030, xy ~ 0.020 • Conclusion: • Probably in this optics luminosity can be not worse than in reference, but because of lack of damping injection was slower. SBRS05 Nov 7 - 8 2005, Frascati, Italy

  11. Experimental study (low fs experiment) • What can we can do more with ? • 2) Reduce ns keeping constant sz/by • In this way we can increase xy, but not luminosity. SBRS05 Nov 7 - 8 2005, Frascati, Italy

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

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

  14. Conclusion • Have experimented with: • Reduced bunch length /low (1.4T) wiggler field • 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 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) 6fv – 2fs = 4f0 6fv = 4f0 fh – fv + fs = f0 fh – fv + fs = f0 2fh – fs = f0 High tune region: 212 < fh < 237 kHz (0.544 < Qx < 0.608) 247 < fv < 272 kHz (0.633 < Qy < 0.697) SBRS05 Nov 7 - 8 2005, Frascati, Italy

  16. Appendix: Tune plane exploration:“low” tune region: 0.513 < Qx < 0.564; 0.590 < Qy < 0.641 fh + fs – fv = f0 2fh – fs = f0 • 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) “Strong” beam – beam interaction. Resonance 2fh – fs = f0 hits working point. • No beam – beam interaction • Seen “machine” resonances • 2fh – fs = f0 • fh – fv + fs = f0 “Mild” beam – beam interaction Resonance 2fh – fs = f0 becomes stronger and moves toward working point. 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 “Strong” beam – beam interaction. Effects of 6fv = 4f0 and 6fv - 2fs = 4f0 spread downward. No good place for working point. • No beam – beam interaction. • Seen “machine” resonance • fh – fv + fs = f0 “Mild” beam – beam interaction Seen “beam-beam” resonances 6fv = 4f0 and 6fv - 2fs = 4f0. • 1 x 1 head-on collision, weak-strong beam-beam interaction. • Tune scan with vertical beam size measurement of the weak (positron) beam. 6fv - 2fs = 4f0 6fv - 2fs = 4f0 6fv = 4f0 6fv = 4f0 fh – fv + fs = f0 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. SBRS05 Nov 7 - 8 2005, Frascati, Italy

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