BEAM-BEAM EXPERIMENT

T. Ieiri, Y. Funakoshi, T. Kawamoto,M. Masuzawa and M. Tobiyama

KEKB Review Feb 21, 2005

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MEASUREMENT OF BEAM-BEAM EFFECTSOutline• Introduction• Beam-Beam Effects• Measurement Method• Measurement of Beam-Beam Kick with Horizontal Scan
 Beam-Beam Tune Shift Dynamic Beta

• Analysis of Results• Summary2
KEKB Review Feb 21, 2005

Motivation• “Egure” phenomena• Effect of electron cloud• Dynamic beam-beam effects• Beam diagnostics with collision3
KEKB Review Feb 21, 2005

Machine Parameters
Parameter

LERHERBeam Energy, E

3.5

8.0GeV

Horizontal Emittance, εx01824nm

Betatron Tune, νx0/νy045.506/43.54

44.512/41.58

Betas at IP, βx*/βy*59/0.52

56/0.65cm

Momentum Compaction, α

3.4

3.4x 10-4

Bunch Length, σl

6.5 to 8.0

6.5 to 7.0mm

Synchrotron Tune, νs

0.025

0.022

Particles per Bunch, Nb

3.7 to 7.1

3.1 to 5.1

Bunch Spacing, Sb

1.8 to 2.4x 1010
m4

KEKB Review Feb 21, 2005

Dynamic Effects

with beam intensity and size,
depending on betatron tune.

$"#Emittance Ratio• Beam parameters change$"&$"%$!"&#!"%'"(!"$'!"#!"(!

!"!# !"!$ !"!% !"!&!
!"'!"!&!"!'!"!#Dynamic_3("(Beam Size at IP#"(!"!%

Beam-Beam Parameter)

Normalized Emittance

Normalized Beta at IP

Nx=0.509'!

!

./0,Dynamic_3'"#.523.512$"'!"#*+,-dynamic%(!"'

Nx=0.540!"&!"%

Nx=0.509!"$!"#!

Beam-Beam Parameter!"!)!"!*!"!$!"!&!"(Beam-Beam Parameter5

KEKB Review Feb 21, 2005

Beam-Beam Kick
• Collision with a position offset at IP distorts an orbit
around the ring due to beam-beam kick.
• A position shift at a detector is:!

• Beam-beam kick depends
on effective beam size, Σx.

" x = (# +x )2 + (# $x )2

141 µm
170 µmBeam-Beam Kick, Relative# det .# *x"X det . =& b'b cos($% ' "( d )2sin($% )Σx=100 µm

0.008
0.006
0.004
0.002
0-0.002-0.004-0.006-0.008-300 -200 -100

0100200300

Horizontal Offset (µ m)6!

KEKB Review Feb 21, 2005

Beam-Beam Tune Shift!"##!"#'Tuneν0ν0+"

B-B H Tune

H Mode!"#&!"#%L Mode!"#$!"#!

!"!% !"!' !"!( !"!) !"$ !"$%

Coherent Beam-Beam Parameter, !++!"

Beam-Beam Parameter+# 0=0.506, # 0 =0.512

X^+ + X^-/1.31

B-B_H_Tune!"'!"!&!"!%!"!$!"!#!

!

!"!'!"!#!"!(!"!$!"!)!" bb•Coherent Beam-Beam Parameter •Beam-Beam Tune Shift!±q=!q0±N mre! ± 2"# q (# x + # y )"# bb $ # H + # L % # 0+ % # 0%$ (% 0+ , % 0& )"q #'% bbY
KEKB Review Feb 21, 2005

Y: Yokoya Factor
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Measurement Method
Comparing beam parameters ofcolliding bunches with those ofa non-colliding pilot bunch

Advantagee+Pilot Bunches
eBucket Address

4831

4835

4839

4843

- Measurement is not affected by an orbit correction.
- Monitors are not required to install near IP.
- Imbalance in gains of a detector is cancelled out due to subtraction.
- An effect of the wake may be compensated by considering themeasurement in a single beam.

Disadvantage- Not simultaneous measurement.
- Difference in the intensity of bunches may make an error.
8KEKB Review Feb 21, 2005

Gated Beam Position Monitor•Two detectors are installed in each ring .
Optics Parameter at Detector w/o Beam-Beam Effect
LER-1
BPM_098

LER-2
BPM_104

HER-1
BPM_097

HER-2
BPM_100

Nx

9.34

9.77

35.35

35.12

Bx(m)
Sensitivity_x

39.29

73.14

21.14

31.89

-0.64

1.00

0.45

0.42

Ny

9.03

9.79

32.83

32.59

By(m)

13.35

5.94

12.5615.98
9KEKB Review Feb 21, 2005

Reproducibility of Measured PositionHorizontal)*+,-#

L/H_5/13/03_stability(!

*+,-.#

L/H_5/13/03_stability

&!

'!

%!

Ave:318.6
Std: 15.5$!
#!

HER_Phase

H/11/11/00_sta

Ave:56.9
Std: 9.1%!
$!

Mean:36.00
Std:0.05

Ave.:36.00
Std.: 0.05 deg%!

&!
CountsCountsPhase

Counts&!

Vertical$!
#!

#!

"!

"!

"!

!
#'!

µ

#(!

$!!

$#!

$%!

$'!

LER Horizontal Position (µm)

!
!

#!

%!

'!

)!

"!!

µ

LER Vertical Position ( µm)!
$&'($&')$*$*'"$*'#Phase (deg)•Resolution is about 10 µm in position and 0.05 deg in phase.
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KEKB Review Feb 21, 2005

Measurement in Normal Run•Collision is normally performed with a horizontal offset !
VerticalPosition Shift

Horizontal
Position ShiftOFFSET

Detected at LER-2 on Dec. 11, 2003
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KEKB Review Feb 21, 2005

Measurement with Horizontal Scan

•Scanning Conditions
ScanNo.

Bunch
Spacing
Sb (bucket)

Bunch
Current
Ib+/Ib-(mA)

NumberofBunchesTuneνx0+/νx0-Memo1

3.77

0.43/0.29

1289

0.511/0.514

LowCurrent

23.77

0.78/0.67

1289

0.511/0.512

HighCurrent

324

0.62/0.52

203

0.510/0.508

WideSpacing

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KEKB Review Feb 21, 2005

Scan-1/ low current, normal spacing

Luminosity and LER Vertical Beam Size

'2500

&2000

%

1500

$

1000

#500

"

0-300 -200 -100!

0100 200

Horizontal Offset ( µm)

Horizontal Tune Shiftscan_1

V_Size LER

Luminosity

3000

x 103 0 cm-2 s-1

Beam-Beam Tune Shift
0.04

6/09/04_1

Δνbb

0.03
0.02
0.01
0-300 -200 -100 0 100 200 300

Horizontal Offset ( µm)

13KEKB Review Feb 21, 2005

Egure30x 10 cm s

scan_3

67500

56000

44500

33000

21500

10-300 -200 -100

0V_Size LER

Luminosity

9000-2 -1

Horizontal Tune ShiftScan-2/ high current, normal spacing
6/09/04_3

0.04
0.03
0.02
0.01

0-300 -200 -100 0 100 200 300

Horizontal Offset ( µm)

Tune Spectrum

0100 200 300

Horizontal Offset ( µ m)

verticalhorizontal
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KEKB Review Feb 21, 2005

Scan-3/wide spacing

Luminosity and LER Vertical Beam Size

Beam-Beam Tune Shift

No Egure-2 -1600

6400

4200

200-300-200-100 0 100 200 300

0.04

H_Tune Shift

8LER Vertical Size

Luminosity

30

800 x 10 cm s (b)scan6_1

0.03
0.02
0.01
0-300 -200 -100 0100 200 300

Offset ( µ m)

Horizontal Offset (µ m)•Luminosity curve is almost symmetrical.
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KEKB Review Feb 21, 2005

Why is the luminosity asymmetricalin the horizontal scan ?

• The tail part of a positron bunch is(a)vertically unstable due to e- cloud.

Xe!"

(b)

SXe-!"(c)S

longitudinal colliding position shifts,depending on the horizontal offset.

• The electron beam may stimulate
the electron cloud in offset (c).

X!"

• For the sake of a finite crossing angle,e- S• The vertical size of the positron beamincreases due to synchro-beta coupling.

• Therefore, the luminosity reduces in (c).
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KEKB Review Feb 21, 2005

Position Shift and Beam-Beam Kick
• Position shift depends on the beta function,+,-./01+,-./2##3$
Dynamic_4!")

%'!
%!!

!"'

$'!

Betax_IP

Betax_D11-2!"(!"&$!!

!"%

#'!

!"$#!!

!"#'!

!

!
!"#!

!"!$ !"!& !"!( !"!*Beam-Beam Parameer!

Sqrt(Beta*Beta_D11-2)• But, " D11#2" * is almost constant.

the beta changes due to dynamic effects.

$mDynamic_4%%&%' %&%( %&%" %&%$ %&)#"!

Beam-Beam Parameer• We can obtain beam-beam kickfrom position shift.
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KEKB Review Feb 21, 2005

Dynamic Horizontal Beam Size at IP• Intensity normalized beam-beam kick curves with different current"scan_1_kick"

#!#$%
!"
!&##!'##!"## # "##'##&##H Offset

0.43 x 0.29 mA2Σx = 141 µm

scan_3_kickdH(1-3)dH(2-3)
Cal_80/2#$%

dH(1-3)dH(1-3)#$%dH(1-3)dH(2-3)
Cal_100/2#!#$%!"!&##!'##!"## # "##'##&##H Offset

0.78 x 0.67 mA2
Σx = 113 µm• Beam size reduces as the current increases.
Effective size w/o dynamic effect : Σx0 = 155 µm
KEKB Review Feb 21, 2005

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Ratio of Beta Function
for Two Locations• A ratio of position shift for two locations provides
a beta function ratio there, regardless of beam-beam kick.
Beta_cal1"X 2# 2 cos( %& ' "( 2 )=$"X1#1 cos( %& ' "(1 )Sensitivity, L098/L104!"#*!"#)!"#(!"#'!"#&!"#%!"#$""#"+ "#") "#"' "#"%"#,

Beam-Beam Parameter• A measured ratio is different from calculation.
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KEKB Review Feb 21, 2005

Sum Emittance (nmrad)

Dynamic Emittance• Sum emittance is obtained

Dynamic_1'"

from beam-beam tune shift&"

L-mode Tune%"$"

" +x + " #x =H-mode Tune

#"!""

(!

$&)"

re N + N #1% ( # + + )% +2$ &&' x + ' #x

Normalized Intensity

Normalized Intensity X10 6•

Sum emittance measured agrees with calculation
using H-mode tune, not L-mode tune.
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KEKB Review Feb 21, 2005

Summary• Collision at KEKB is performed with a horizontal
offset to avoid the “Egure”.
• The “Egure” phenomena should be caused byelectron cloud.
• Horizontal beam size at IP agrees with expectation.
• A measured ratio of beta function for two locations
is different from calculation.
• Dynamic emittance agrees with calculation
using H-mode tune.
• The presence of dynamic effects was demonstrated
by these experiments.
21KEKB Review Feb 21, 2005