Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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Quadrupole Pick-upsQuadrupole Pick-ups

What is a quadrupole pick-up? PS pick-ups and experimental results. Can we do the same in the LHC?

OutlineOutline

A. Jansson PS/OP

Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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What is a quadrupole pick-What is a quadrupole pick-up?up?

A non-invasive instrument sensitive to r.m.s. beam size.

Uses the non-linear terms in electrode response to particle position (very small) to measure quadrupole moment.

Beam

Pick-up seen along beam path

A

BD

C

Vacuum chamber

moment quadrupoleDCBAC)(A-D)(B 2222

x yxy

2

2222

221Ar

yxryi yx

b

Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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PS quadrupole pick-upPS quadrupole pick-up Position contribution can not

be avoided, but can be measured and subtracted.

Design suppresses the dominating intensity signal by coupling to the radial magnetic field component.

Induction loop

Pick-up seen along beam path

A

BC

D

Flux lineBeam

2

2222

23.141.00Ar

yxry

rxi yx

b

Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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Installation in PSInstallation in PS

h v Dh

SS 03 22 m 12 m 3.2 mSS 04 12 m 22 m 2.3 m

“One pick-up per plane”

Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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0

20

40

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140

Number of machine revolutionsQ

uadr

upol

e m

omen

t (m

m2)

QPU4

QPU3

Beam: EASTBDate: March 28, 2001

First signals 2001First signals 2001 Large beam size oscillations

detected at start-up (due to wrong magnet settings in transfer line).

Quadrupole moment evolution after PS injectionPosition contribution has been subtracted

First 10-20 turns are used to measure matching.

Values after filamentation are used to check position correction and measure filamented emittance.

Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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)(

)()(

2

2

2

222

22

22

yxx

x

yx

q

y

q

x

q

xxp

q

yyy

q

xxx

yx

DDDDD

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60

-1 1 3 5 7 9

Turn

Qua

drup

ole

mom

ent [

mm

2]

10 free parameters, 20 data points

Measurement of matchingMeasurement of matching

Simultaneous fit to the two pick-up signals gives: Injected emittances. Betatron mismatches. Horizontal dispersion

mismatch.

Input parameters H, V, DH, H, V,p,qh,qv

Most input parameters can be checked experimentally

Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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Injection matching Injection matching measurementmeasurement Betatron mismatch

Dispersion mismatch

Emittance

0

0.2

0.4

0.6

0 0.5 1 1.5Horizontal

Verti

cal

ReferenceQNO40 -10AQNO40 -20A

Dispersion Matching

-0.5

-0.25

0

0.25

0.5

-0.5 -0.25 0 0.25 0.5

dd/sqrt(b)

dd' s

qrt(

b) +

a s

qrt(

b) d

d

Horizonal Matching

-0.8

-0.4

0

0.4

0.8

-0.8 -0.4 0 0.4 0.8

db/ba

db/b

- da

Vertical Matching

-0.4

-0.2

0

0.2

0.4

-0.4 -0.2 0 0.2 0.4

db/b

a db

/b -d

a

k

'DD

D

kD

Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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Measurement of Measurement of filamented emittancefilamented emittance For a stable beam, the

emittance can be calculated from two (constant) pick-up readings.

Different horizontal/vertical beta function ratios at the two pick-ups are required.

Signal noise is reduced by averaging over many turns.

22

2222

21

2111

22

xpyyxx

xpyyxx

yx

D

D

0

0.5

1

1.5

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2.5

QPU 3/4 WS H54 WS H64

Emitt

ance

(um

)

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0.2

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0.4

0.5

0.6

0.7

QPU 3/4 WS V65

Emitt

ance

(um

)

Horizontal

Vertical

Wire-scanners

Quad PUs

Statistical error

Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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Beam based calibrationBeam based calibration

Comparison Quad PU vs. Wire-scanner on stable beam.

Several different beam types.

Systematic error from: Beta function ~10% Dispersion ~10% Mom. spread ~3%

QPU3

0

20

40

60

80

100

120

140

160

180

0 20 40 60 80 100 120 140 160 180WS + tomoscope [mm2]

QP

[mm

2]

SFTPROEASTBEASTCADLHCEASTAideallab meas

QPU4

-20

0

20

40

60

80

-20 0 20 40 60 80WS +tomoscope [mm2]

QP

[mm

2]

Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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SensitivitySensitivity

Estimated from measurement on stable beam.

Fluctuation lower than 0.5 mm2 r.m.s. (4 1011 p/bunch ).

This corresponds to a 1-2% beta beating at PS injection.

Improvement still possible.0

5

10

15

20

25

30

1 4 7 10 13 16 19 22 25 28 31 34 37 40

Turns

Qua

drup

ole

Mom

ent (

mm

2)

QPU3

QPU4

Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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Can the same pick-ups be Can the same pick-ups be used in LHC?used in LHC?

The pick-ups were optimized for the LHC beam parameters at injection into the PS.

The most important difference between PS and LHC is the bandwidth requirement .

PS SPS LHC

Bunch length 50 ns 1 ns 1 ns

Bunch spacing 300 ns 25 ns 25 ns

Max beam size 5 mm 4 mm 1.2 mm

Chamber radius 76 mm 78 mm 22 mmNote that a design that works in the SPS would work in the LHC!

Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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A pick-up adapted for the A pick-up adapted for the LHCLHC

At high frequencies, the loops essentially behave like badly matched strip-line couplers.

B

PS: magnetic induction loop

50OUT

B

LHC/SPS: strip line couplers

50 5050

50180°

0°

0°

0°

J.M. Belleman,PS/BD/Note 99-09

60dB

Replace each loop with two matched strip-lines and a wideband hybrid.

Good hybrid required (available).

Transfer impedances x10 larger than in PS.

Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, 2001

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SummarySummary Quadrupole pick-ups can measure continuously without

perturbing the beam.

Both matching and emittance can be measured, on each bunch individually.

The results in the PS have been very good.

It can be done in the LHC, e.g. using strip-line couplers.