T. IeiriýKEKB Review Committee,

Feb. 10 2003

1

OutlineĂTune Measurement- Beam-Beam Tune ShiftĂBunch Length Measurement- Monitor based on Beam Spectrum- Bunch Lengthening and ShorteningĂBunch-by-Bunch Position- BPM System- Bunch-by-bunch OrbitĂSummary

T. IeiriýKEKB Review Committee,

Feb. 10 2003

2

Beam-Beam Tune Shift• Tunes in Beam-Beam Collision (H- & L- modes) :(cos µ H + cos µ L ) − (cos µ +0 + cos µ0− ) = −2 π {Ξ+q sin µ0+ + Ξ −q sin µ −0 }• Coherent Beam-Beam Parameters:0±βr
Nq
Ξ±q = m eRq±
γ ± 2 πΣq (Σ x + Σ y )ξq ≈ Ξ +q + Ξ−qΣq = (σ q+ )2 + (σ q− )2• Luminosity:+−f0 N b+γ + T Ξ y + Ξ y  RL
L=⋅⋅
⋅ *
*
re1+ T  β y  Ry
• Emittance:+rN*
ε +x + ε −x = + e − ⋅(1+T)⋅Rx−Ξ x + Ξ x 2πγ

I −γ −
T= +I γ+Rq* : reduction factors
Assuming a flat beam and β x+ ≈ β x− = β *x

T. IeiriýKEKB Review Committee,

Feb. 10 2003

3Beam-Beam Tune Shift (cont’d)Beam-Beam Tune Shift, calculation∆ν b−b = ν H + ν L − ν 0+ − ν 0−

ν =.512, .522

H mode✳✱✸✷✳✱✸✶L mode✳✱✸✵✳✱✸✴

✳

✳✱✳✴ ✳✱✳✵ ✳✱✳✶ ✳✱✳✷ ✳✱✳✸ ✳✱✳✹Coherent Beam-Beam Parameter

Tune Shift✳✱✸✹✳✱✸✸✳✱✳✹∆ν b-b0✳✱✸✺

Horizontal Tune•

✳✱✳✸
✳✱✳✷

(.571, .589)

✳✱✳✶
✳✱✳✵

(.512, .523)

✳✱✳✴
✳

✳

✳✱✳✴ ✳✱✳✵ ✳✱✳✶ ✳✱✳✷ ✳✱✳✸ ✳✱✳✹Coherent
Beam-Beam Parameter

T. IeiriýKEKB Review Committee,

Feb. 10 2003

+−

Ξ +Ξ4

Measurement of Beam-Beam Tune
• Measurements of pilot bunch and collision bunches are usefulfor beam-beam study.
• Beam-beam tune shift is studied by measuring both tunes.

e+!

!

Pilot Bunches

eBucket Address

4885

4889

4893

T. IeiriýKEKB Review Committee,

4897
Feb. 10 2003

5

Measurement of Beam-Beam Tune (cont’d)- Two beam-beam modes
LERHER

H. L-mode
H. L-mode

V. L-mode
V. H-mode
H. H-mode

H. H-mode

Non-Collision Tunes are .5124, .5712.5221, .5903

T. IeiriýKEKB Review Committee,

Feb. 10 2003

6

F8099 March 25, 2002❜❧❋✳✱✳✸✳✱✳✸✳✱✳✷✳✱✳✶✳✱✳✶−✳✱✳✷+✳✱✳✵✳
✻✳✳

✳✱✳✵✳✱✳✴

✳✱✳✴

✼✳✳

✴✳✳✳

✴✴✳✳

LER DCCT (mA)✫❧❦p❜✬✳
✳✱✷✴✵✳✳

F8099 March 25, 2002✻✳

R *x =1.0

w. Yokoya Factor

w/o Yokoya Factor

Luminosity−+✻✹✳
✸✳

calculation✷✳
✶✳

✵✵✱✴

✵✱✵✳✱✷✸✳✱✸✳✱✸✸

I + T/(1+T) (mA)✳✱✹RL✴✳

✺✳

ε +εVertical Beam-Beam Parameter❜❧❚

Ξ +ΞBeam-Beam Tune Shift

Measurement of Beam-Beam Tune (cont’d)- Current dependence

R *y❏s❦❣✲rs❧❝❏s❦❣✲❆q❣

= 1.0✹✷✵+✵✱✶(1+T)I b (mA)✵✱✷✵✱✸✳
✻✳✳

T. IeiriýKEKB Review Committee,

✼✳✳

✴✳✳✳

✴✴✳✳

✴✵✳✳

LER_DCCT (mA)

Feb. 10 2003

7

Measurement of Beam-Beam Tune(cont’d) - Complexity

Two peaks appears, when vertical offset is given.
Nonlinearity in vertical spectrum

tune

T. IeiriýKEKB Review Committee,

Feb. 10 2003

8Bunch Length Monitor
based on Beam Spectrum• Amplitude of Spectrum :ωt <1• Rms Bunch Length :
σ≡

t2 =

1
Amplitude 1
F(ω ) ≈ I 0 1 − t 2 ω 2  2

Beam Spectrum

1.22F(ω1 )ln∆ω 2 F(ω2 )∆ω = ω2 − ω1

0.8
0.62mm
4mm
6mm
10mm

0.4
0.2
002468Frequency (GHz)

10Note: This measurement does not depend on bunch structures.
T. IeiriýKEKB Review Committee,

Feb. 10 2003

9Bunch Lengthening
Single Bunch in HER

10Bunch Length (mm)Bunch Length (mm)1286

rms meas.
FWHM calrms cal.
streak4
2000.5
11.5
Bunch Current (mA)

Single Bunch in LER

10286❅❏◗❛❥

4
2
000.5
11.5
Bunch Current (mA)•Lines are calculated rms bunch length assuming purely inductive impedance,
results in Z i / n = 0.076 Ω for HER and =0.072 Ω for LER.

•Estimated impedance is 5 times larger than the design of 0.015 Ω.

•

Need to resolve the disparity between measurement and design.
T. IeiriýKEKB Review Committee,Feb. 10 2003

210

Reducing the bunch length
Natural bunch length : σ 0 =Vc= 5.0 MV

987

α= 2.4x10 -465∆43• (2) Raise cavity voltage, Vc∆

α= 1.1X10 -40 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Bunch Current (mA)

Bunch Length (mm)Bunch Length (mm)

• (1) Reduce momentumcompaction, αcαδεωs10

Vc=8MV987∆654

Vc=11MV∆00.2 0.4 0.6 0.8T. IeiriýKEKB Review Committee,

1

1.2 1.4 1.6

Bunch Current (mA)
Feb. 10 2003

11Bunch Length Calculation
with P.W.D.

Normalized Bunch Length• Both methods reduce B.L. to 70% at zero intensity.
• Higher Vc makes shorter B.L. at high intensity.
2
1.8
1.6
1.4
1.2
10.8
0.6
✳

Note:
• Higher Vc has advantage of beam

Ref.
0.5 αloading.
•Short bunch length produces high
HOM power.

2Vc

✳✱✸✴

✴✱✸

Intensity✵T. IeiriýKEKB Review Committee,

Feb. 10 2003

12

Turn-by-Turn & Bunch-by-Bunch
Beam Position Monitorfeatures• Share the button signal with the COD measurement.
• Intensity, orbit and synchronous phase are measured
using an I/Q demodulator working at the rf frequency.
• The gate enables to measure the bunch-by-bunch
parameters.
• Resolution : < 0.1 degrees in phase, < 10 µm in orbit
with averaging.
T. IeiriýKEKB Review Committee,Feb. 10 2003

13

Bunch-by-bunch Orbit- Effect of Orbit Bump

! Bunch-by-Bunch Position Sensitivity✇✣❀✣✳✱✼✻✳✷✶✣✮✣✴✱✳✹✻✸✈✣P❀✣✳✱✼✼✹✴✻✣✇✣❀✣✴✱✸✹✻✵✣✮✣✴✱✳✺✴✴✈✣P❀✣✳✱✼✼✺✴✻✣✇✣❀✣✴✱✷✷✴✺✣✮✣✴✱✳✹✴✺✈✣P❀✣✳✱✼✼✹✼✺✣✇✣❀✣✳✱✳✼✹✼✸✹✣✮✣✴✱✷✼✴✻✈✣P❀✣✳✱✼✼✻✷✵✣✇✣❀✣✳✱✳✺✶✼✻✹✣✮✣✴✱✷✺✺✻✈✣P❀✣✳✱✼✼✺✹✺✣✇✣❀✣✰✳✱✳✵✶✸✼✼✣✮✣✴✱✷✺✼✻✈✣P❀✣✳✱✼✼✺✺✷✣✰✳✱✸❋✦✷✹✳✼❋✦✵✳✴
❋✦✵✴

✰✴

✰✴✱✸✰✵✰✴✱✷✰✴✱✵✰✴

✰✳✱✻

✵

V-Position (mm)H-Position (mm)✳

✰✳✱✹✰✳✱✷✰✳✱✵❚✦✵✴
❚✦✵✳✴

✴✱✸❚✦✷✹✳✼✴
✳✱✸
✳
✰✳✱✻

✰✳✱✹

H_Bump (mm)✰✳✱✷✰✳✱✵✳

✳✱✵

V_Bump (mm)Position Sensitivity for each bunch is consistent within 1%.
T. IeiriýKEKB Review Committee,Feb. 10 2003

14

Bunch-by-bunch Orbit- Effect of IP Horizontal Bump, Preliminary

collision

Non-collision
3/4/02_b-b/2•

Collision offset makes an orbit
displacement around the rings.

•Beam-beam effect can be
estimated from an orbit
difference between collision andnon-collision bunches.

0.7
HER_V_Position (mm)HER_H_Position (mm)Orbit displacement exists
between collision and noncollision bunches. real ?

❋❈P❚✳
❋❈P❚✶✳

❋❈P❋✶✳
❋❈P❋✳

2.5

•

2.45

0.65

2.4

0.6

2.35

0.55

2.3
0.5
84 86 88 90 92 94 96 98
Bucket Number 48##
T. IeiriýKEKB Review Committee,Feb. 10 2003

15

Bunch-by-bunch Orbit
in irregular 4-bucket spacing

Phase (deg)✶PP_att✵✱✸
✵
✴✱✸
✴
✵✼✻✳

✵✼✼✳

✶✳✳✳

✶✳✴✳

Bucket Number✶✳✵✳

Horizontal Position (mm)• We observed jumps in phase and in orbits at 5-bucketspacing.
• Attenuators inserted near the buttons reduced the jumps.
• Measurements are influenced by mismatch between buttons
and the detector.
555H
H_att✰✳✱✴
✰✳✱✵5✰✳✱✶✰✳✱✷✰✳✱✸
✰✳✱✹
✵✼✻✳

T. IeiriýKEKB Review Committee,✵✼✼✳

✶✳✳✳

✶✳✴✳

Bucket NumberFeb. 10 2003

✶✳✵✳

16

Positions along Train

Phase (deg)

0.5
0-0.5
-1-1.50Orbit (mm)

1.5

LER

H1
V1
H2V2

1000 2000 3000 4000 5000

BucketL/2/5/03

1150 mA
1187 bunches

10-0.5-105

P1P21000 2000 3000 4000 5000

L/2/5/03

1150 mA, 1187 bunches

432P1P2

10-1

1000 2000 3000 4000 5000

Bucket

660 mA, 1187 bunches

Bucket

H1V1
H2
V20.5

H/2/5/03

32.5
21.5
10.5
0-0.5
0

Phase (deg)HER

Orbit (mm)660 mA
H/2/5/03 1187 bunches
1T. IeiriýKEKB Review Committee,

01000 2000 3000 4000 5000

BucketFeb. 10 2003

17

Summary• Beam-beam tune shift– Detected beam-beam modes under unequal tunes.
– Estimated luminosity is roughly consistent with theluminosity monitor.
– Estimated emittance is larger than calculation, suggests thedynamic effect.

T. IeiriýKEKB Review Committee,

Feb. 10 2003

18

Summary (cont’d)• Bunch lengthening– We need to check the impedance sources, to explain theunexpected bunch lengthening.
– Raising Vc is more effective than reducing α, to make thebunch length short .

• Bunch-by-bunch position– Beam-beam offset could be measured from an orbit
displacement.
– Orbit along train stays within +/- 0.1 mm.

T. IeiriýKEKB Review Committee,Feb. 10 2003

19