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

Effect of high synchrotron tune on BeamBeam interaction: simulation and
experiment
A. 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
•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
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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
160
10
8
I- total
I+ total
Luminosity
7
8
120
6
6
100
5
80
4
2
60
3
0
140
e- beam
e+ beam
3 April 2005 CESR-c running, April 3 2005,
vertical beam size
3 April 2005 CESR-c running, April 3 2005
12
10
8
sy
6
4
4
2
0
12
14
16
18
20
22
24
Time[hr]
40
2
20
1
0
0
12
14
16
18
20
22
24
Time[hr]
•Max Luminosity: ~
1030
6.2x1031 1/cm2/sec,
e- beam
e+ beam
3 April 2005 CESR-c running, April 3 2005,
vertical beam -beam tune shift
1.5
x
per 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.
xy
1/cm2/sec
0.07
0.07
0.06
0.06
0.05
0.05
0.04
0.04
0.03
0.03
0.02
0.02
0.01
0.01
0
0
12
14
16
18
20
22
24
Time[hr]
3 April 2005 CESR-c running, April 3 2005,
horizontal beam-beam tune shift parametr
e- beam
e+ beam
0.035
0.035
0.03
0.03
0.025
xx
0.025
0.02
0.02
0.015
0.015
0.01
0.01
0.005
0.005
0
0
12
SBRS05 Nov 7 - 8 2005, Frascati, Italy
14
16
18
20
22
24
Time[hr]
4
Synchrotron tune and phase modulation
Description:
Vertical  - function and phase as

s 
d~
s
*
 ( s)   1  *2 ;  ( s)   ~
  
 (s )
0


a
sn  s z z cos( 2 s  n) - longitudin al position of collision
2
as a function of turn number
Phase modulation between collisions :
 ( sn 1 )   ( sn )
sn 1  sn


2 
2

s
2 * 1  2 
 * 


s a
1
 s * z z cos( 2 s  n)
 2
 s z a z 2 
1 

*2 

8


2
*
function of z near IP,  = 11mm.
s
200
0.2
100
0.1
0
0

y
-100
-0.1

y
-200
-0.2
-40
-20
0
20
40
z[mm]
For CESR-c sz/* ~ 1  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
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Single particle tracking
BBI with round beam with turn-to-turn phase modulation: x  0.033, s/  1,
as=1. Tune scan from 220kHz (Q = 0.564) to 245kHz (Q = 0.628)
fs = 39kHz (s= 0.10)
fs = 0
fs = 19.5kHz (s= 0.050)
(1+4s)/2
(1+2s)/2
8/14
7/12
6/10
5/8
(1+3s)/2
SBRS05 Nov 7 - 8 2005, Frascati, Italy
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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
 ss z
*
in machine ?
1) Reduce sz keeping constant s and y
s 
z
c  f0 s E s E
;
 Bw
2  s E
E
in wiggler s diminated rings
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
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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
SBRS05 Nov 7 - 8 2005, Frascati, Italy
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Experimental study
(1.4T wiggler field optics)
12 wigglers 1.4T optics luminosity performance.
8 trains x 1 bunch, CESR-c MS, March 1 2005
Lum
e- tot [mA]
e+ tot [mA]
16
160
14
140
12
120
10
100
8
80
6
60
4
40
2
20
0
250
300
350
400
0
450
Time [min]
12 wigglers 1.4T optics luminosity performance.
8 trains x 1 bunch, CESR-c MS, March 1 2005
0.035
0.035
<ksi_x>
<ksi_y>
0.03
0.03
0.025
0.025
0.02
0.02
0.015
0.015
0.01
0.01
0.005
0.005
0
250
300
350
400
Time [min]
450
0
•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
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Experimental study
(low fs experiment)
What can we can do more with
 ss z
*
?
2) Reduce s keeping constant sz/y
 s 0.1  0.05 (reduced RF voltage) ;
s z 12mm  24mm, have to change  from 12 to 24mm.
y
In this way we can increase xy, but not luminosity.
SBRS05 Nov 7 - 8 2005, Frascati, Italy
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Experimental study
(low fs experiment)
Colliding &
non-colliding
beam
spectrum
Interesting
moment:
xx 
nb re 1
I A
 1.98 10 6
;
2  x
 x [ m]
I  0.5 10 3 A,  x  1.15 10 7 m, x x  0.0086  3.357 kHz
x y  xx
y s x
;  x  0.82m,  y  0.011m, s y  2.66 10 6 m
x s y
x y  0.0133  5.2kHz
SBRS05 Nov 7 - 8 2005, Frascati, Italy
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Experimental study
(low fs experiment)
High fs optics: fs = 39kHz s=0.100),
y=12.7mm, sl=12mm, d = ssl/y=0.0944
0.8x0.8mA
collision
xx ~ 0.015
xy ~ 0.020
Low fs optics: fs = 18kHz, s=0.046),
y=21.5mm, sl=26mm, d = 0.0558
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
One can see xy saturation, i.e., L/I is not growing.
With lower fs we have reached
higher xy !!!
SBRS05 Nov 7 - 8 2005, Frascati, Italy
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Conclusion
•
Have experimented with:
•
Experiment 1), probably, and 2), definitely,
indicated that vertical betatron phase
modulation between collisions resulted from
high fs has negative impact on CESR-c beambeam performance.
•
Simulation results are in agreement with
experiments.
1. Reduced bunch length /low (1.4T) wiggler field
2. Low fs
SBRS05 Nov 7 - 8 2005, Frascati, Italy
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Appendix: Tune plane exploration:
“high” and “low” tune region maps.
Low tune region:
200 < fh < 220 kHz (0.513 < Qx < 0.564)
6fv – 2fs = 4f0
230 < fv < 250 kHz (0.590 < Qy < 0.641)
2fh – fs = f0
6fv = 4f0
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
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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)
Frame 002  02 Apr 2004  CESRc 6WIGS tune scan, 04/01/2004, single e+
SigP, single e+ beam
fv[kHz]
245
240
235
2fh – fs = f0
230
200
205
210
215
fh[kHz]
No beam – beam interaction
Seen “machine” resonances
1)
2fh – fs = f0
2)
fh – fv + fs = f0
“Mild” beam – beam interaction
Resonance 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
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Appendix: Tune plane exploration:
“High” 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.
4,
single002
e+ 
beam
Frame
02 Apr 2004  Single e+, high fv/fh, Flat route,25x25kHz
270
fv[kHz]
6fv - 2fs = 4f0
6fv - 2fs = 4f0
260
6fv = 4f0
6fv = 4f0
250
220
230
fh[kHz]
No beam – beam interaction.
Seen “machine” resonance
1)
fh – fv + fs = f0
“Mild” beam – beam interaction
Seen “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.
SBRS05 Nov 7 - 8 2005, Frascati, Italy
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Appendix: Tune plane exploration:
Conclusion
•In the “high” tune region beambeam performance limited by beambeam interaction driven resonances.
We can not eliminate them.
•In the “low” tune region “machine”
driven resonances affect the beambeam performance. We can damp
them.
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