andreas jansson, "quadrupole pick-ups", lhc bi-review, november 19-20, 2001 1 quadrupole...
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Andreas Jansson, "Quadrupole Pick-ups", LHC BI-Review, November 19-20, PS 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 line BeamTRANSCRIPT
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
5
0
20
40
60
80
100
120
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
0
10
20
30
40
50
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
2
2.5
QPU 3/4 WS H54 WS H64
Emitt
ance
(um
)
0
0.1
0.2
0.3
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.