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
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
0
20
40
60
80
100
120
140
160
0
1
2
3
4
5
6
7
8
12 14 16 18 20 22 24
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.
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
12 14 16 18 20 22 24
3 April 2005 CESR-c running, April 3 2005,vertical beam -beam tune shift
e- beame+ beam
Time[hr]
0
2
4
6
8
10
0
2
4
6
8
10
12
12 14 16 18 20 22 24
3 April 2005 CESR-c running, April 3 2005,vertical beam size
e- beame+ beam
Time[hr]
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
12 14 16 18 20 22 24
3 April 2005 CESR-c running, April 3 2005,horizontal beam-beam tune shift parametr
e- beame+ beam
Time[hr]
x
y
y
SBRS05 Nov 7 - 8 2005, Frascati, Italy 5
Synchrotron tune and phase modulation
Description:
-200
-100
0
100
200
-0.2
-0.1
0
0.1
0.2
-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)
SBRS05 Nov 7 - 8 2005, Frascati, Italy 6
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
SBRS05 Nov 7 - 8 2005, Frascati, Italy 7
Phase modulation effect:Multi-particles tracking (D. Rubin)
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)
* zs
rings diminated sin wiggler;2
0wBE
EEE
s
fcz
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 ~ 2.2x1030 at 2mA2.1T, L ~ 2.0x1030 at 2mA
SBRS05 Nov 7 - 8 2005, Frascati, Italy 10
Experimental study(1.4T wiggler field optics)
0
2
4
6
8
10
12
14
16
0
20
40
60
80
100
120
140
160
250 300 350 400 450
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]
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
250 300 350 400 450
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.
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)
* zs
24mm. to12 from y change tohave ,2412; voltage)RF (reduced 05.01.0
mmmmz
s
SBRS05 Nov 7 - 8 2005, Frascati, Italy 12
Experimental study (low fs experiment)
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:
SBRS05 Nov 7 - 8 2005, Frascati, Italy 13
0.8x0.8mA collisionx ~ 0.015y ~ 0.020
2.0x2.0mA collisionx ~ 0.026y ~ 0.025
3.0x3.0mA collisionx ~ 0.041y ~ 0.025
Experimental study (low fs experiment)
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.
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.
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
= f0fh –
fv + fs
= f0
fh –
fv + fs
= f0
6fv = 4f0
6fv – 2fs = 4f0
SBRS05 Nov 7 - 8 2005, Frascati, Italy 16
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.
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
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
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.