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

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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
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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

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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.

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CESR-c operation example

• Max Luminosity 6.2x1031 1/cm2/sec, 1.5 x 1030
  1/cm2/sec per bunch.
• Max Current per bunch 2.0mA.
• Max beam-beam perameters
• xy() 0.035, xy(-) 0.019, ltxygt 0.026
• xx() 0.025, xx(-) 0.03, ltxxgt 0.027
• e beam current is limited by long range
  beam-beam interaction.

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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 _at_5.5GeV 0.05, DAFNE
0.003, DORIS 0.005?, VEPP- 4 0.012)
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Single particle tracking
BBI with round beam with turn-to-turn phase
modulation x 0.033, s/b 1, as1. 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)
6/10
8/14
5/8
7/12
(14ns)/2
(12ns)/2
(13ns)/2
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Phase modulation effect Multi-particles tracking
(D. Rubin)
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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

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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
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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.

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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.

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Experimental study (low fs experiment)
Colliding non-colliding beam spectrum
Interesting moment
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Experimental study (low fs experiment)
High fs optics fs 39kHz (ns0.100),
by12.7mm, sl12mm, d nssl/by0.0944
Low fs optics fs 18kHz, (ns0.046),
by21.5mm, sl26mm, d 0.0558
With lower fs we have reached higher xy !!!
One can see xy saturation, i.e., L/I is not
growing.
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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.

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Appendix Tune plane explorationhigh and
low tune region maps.
Low tune region 200 lt fh lt 220 kHz (0.513 lt Qx
lt 0.564) 230 lt fv lt 250 kHz (0.590 lt Qy lt 0.641)
6fv 2fs 4f0
6fv 4f0
fh fv fs f0
fh fv fs f0
2fh fs f0
High tune region 212 lt fh lt 237 kHz (0.544 lt Qx
lt 0.608) 247 lt fv lt 272 kHz (0.633 lt Qy lt 0.697)
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Appendix Tune plane explorationlow tune
region 0.513 lt Qx lt 0.564 0.590 lt Qy lt 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 fh205kHz (Qh0.526),
  fv 235kHz (Qv0.603)

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.
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Appendix Tune plane exploration High tune
region 0.513 lt Qx lt 0.564 0.590 lt Qy lt 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.

6fv - 2fs 4f0
6fv - 2fs 4f0
6fv 4f0
6fv 4f0
fh fv fs f0
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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.