Title: Effect of high synchrotron tune on Beam-Beam interaction: simulation and experiment
1Effect 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
2Content
- 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
3CESR-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.
4CESR-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.
5Synchrotron 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)
6Single 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
7Phase modulation effect Multi-particles tracking
(D. Rubin)
8Experimental 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
9Experimental 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
10Experimental 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.
11Experimental 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.
12Experimental study (low fs experiment)
Colliding non-colliding beam spectrum
Interesting moment
13Experimental 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.
14Conclusion
- 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.
15Appendix 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)
16Appendix 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.
17Appendix 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
18Appendix 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.