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

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

and experiment

A. Temnykh for CESR operating groupCornell University, Ithaca, NY 14850

USA

SBSR05, Nov 7-8 2005, Frascati, Italy

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


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.


CESR-c operation example

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3 April 2005 CESR-c running, April 3 2005

I- totalI+ total

Luminosity

Time[hr]

•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:y(+) ~ 0.035, y(-) ~ 0.019, <y> ~ 0.026x(+) ~ 0.025, x(-) ~ 0.03, <x> ~ 0.027•e+ beam current is limited by long range beam-beam interaction.

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3 April 2005 CESR-c running, April 3 2005,vertical beam -beam tune shift

e- beame+ beam

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3 April 2005 CESR-c running, April 3 2005,vertical beam size

e- beame+ beam

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3 April 2005 CESR-c running, April 3 2005,horizontal beam-beam tune shift parametr

e- beame+ beam

Time[hr]

x

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y


Synchrotron tune and phase modulation

Description:

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-0.1

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-40 -20 0 20 40

Vertical - function and phase as

function of z near IP, * = 11mm.

y

y

z[mm]

2*

2*

2*

2*

11

02*

2*

81

1)2cos(2

122

)()(:collisionsbetween modulation Phase

number turn offunction a as

collision ofposition allongitudin -)2cos(2

)~(

~)(;1)(

zz

szzs

nnnn

sz

zn

s

ana

s

ssss

nas

ssdsss

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)


Single particle tracking

BBI with round beam with turn-to-turn phase modulation: 0.033, as=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 = 05/86/107/128/14(1+2s)/2

(1+3s)/2

(1+4s)/2


Phase modulation effect:Multi-particles tracking (D. Rubin)


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)

* zs

rings diminated sin wiggler;2

0wBE

EEE

s

fcz


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 ~ 2.2x1030 at 2mA2.1T, L ~ 2.0x1030 at 2mA


Experimental study(1.4T wiggler field optics)

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12 wigglers 1.4T optics luminosity performance.8 trains x 1 bunch, CESR-c MS, March 1 2005

e- tot [mA]e+ tot [mA]

Lum

Time [min]

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12 wigglers 1.4T optics luminosity performance.8 trains x 1 bunch, CESR-c MS, March 1 2005

<ksi_x> <ksi_y>

Time [min]

•Limits:•Current per bunch ~ 1.75mALuminosity 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.

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.


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)

* zs

24mm. to12 from y change tohave ,2412; voltage)RF (reduced 05.01.0

mmmmz

s



Colliding & non-colliding beam spectrum

kHz

mmm

kHzmAI

mAIrn

y

yyxy

x

x

yxy

xx

xx

ebx

2.50133.0

1066.2,011.0,82.0;

357.30086.0,1015.1,105.0

;][

1098.112

6

73

6

Interesting moment:


0.8x0.8mA collisionx ~ 0.015y ~ 0.020

2.0x2.0mA collisionx ~ 0.026y ~ 0.025

3.0x3.0mA collisionx ~ 0.041y ~ 0.025


High fs optics: fs = 39kHz s=0.100) y=12.7mm, l=12mm, d = sl/y=0.0944 Low fs optics: fs = 18kHz, s=0.046)

y=21.5mm, l=26mm, d = 0.0558

2.0x2.0mA collisionx ~ 0.041y ~ 0.030

3.0x3.0mA collisionx ~ 0.049y ~ 0.033

With lower fs we have reached higher y !!! One can see y saturation, i.e., L/I is not growing.


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.


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

= f0fh –

fv + fs

= f0

fh –

fv + fs

= f0

6fv = 4f0

6fv – 2fs = 4f0


fh[kHz]

fv[k

Hz]

200 205 210 215230

235

240

245

SigP, single e+ beamFrame 002 02 Apr 2004 CESRc 6WIGS tune scan, 04/01/2004, single e+

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 interactionSeen “machine” resonances1) 2fh – fs = f02) fh – fv + fs = f0

“Mild” beam – beam interactionResonance 2fh – fs = f0 becomes stronger and moves toward working point.

“Strong” beam – beam interaction. Resonance 2fh – fs = f0 hits working point.


Appendix: Tune plane exploration: “High” tune region: 0.513 < Qx < 0.564; 0.590 < Qy <

0.641

fh[kHz]

fv[k

Hz]

220 230

250

260

270

Frame 002 02 Apr 2004 Single e+, high fv/fh, Flat route,25x25kHz

No beam – beam interaction.Seen “machine” resonance1) fh – fv + fs = f0

“Mild” beam – beam interactionSeen “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 =

f06fv = 4f0

6fv - 2fs = 4f0 6fv - 2fs = 4f0

6fv = 4f0


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.

Documents

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