the quadrupole pick-up in the cps -intro and progress report ppc 3 dec 1999 a. jansson
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The Quadrupole Pick-up in The Quadrupole Pick-up in the CPSthe CPS
-intro and progress report-intro and progress reportPPC 3 Dec 1999PPC 3 Dec 1999
A. JanssonA. Jansson
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
OutlineOutline What is a quadrupole pick-up and how does it work? What is special about the pick-up in the PS ring?
Basic ideaPrototype designData acquisition and treatmentMeasurementsRecent design improvements
Ideas for the future... Summary
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
IntroductionIntroduction In a position pick-up, the signal induced by each particle is
thus the total signal gives the beam position
Assume we dispose of a signal
then we can deduce the beam width
xxHxxHi
itotii )(
2222)( xxQxxQ xi
itotii
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
Field Expansion in Field Expansion in Source MomentsSource Moments Assume a single particle (approximated by a line charge)
Maclaurin expansion with respect to source coordinates
Sum (integrate) over all particles in the beam
Where mij are the moments of the beam distribution and Eij are the corresponding electric field components
'
1
rrE
ji r
j
j
i
iji
rrxjxiyxE
, 0''
1
'!
1
'!
1''
jiijij
r
j
j
i
i
ji
ji Emrrxjxi
dydxyxyxE,
0'
, '
1
'!
1
'!
1'''')','(
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
Moments and Field Moments and Field ComponentsComponents
m00 m10
m01
m20
m11
m02
There are n+1 moments of each order n, but never more than 2 orthogonal field components!
dxdyyxyxm jiij ),(
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
The ‘Quadrupole Signal’The ‘Quadrupole Signal’ Measurement of the upright quadrupole field component
gives the so-called quadrupole signal
Signal strenght
Dominating signal
2222220220 ),()( yxdydxyxyxmmQ yx
3
2
22~)(
ppndnd rrEmQ
ppthth rrEmS
1~)(00
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
Quadrupole Signal Quadrupole Signal ComponentsComponents The frequency components of the quadrupole signal
yyxx
yxx
x
yx
qqqq
q
yp
q
xp
q
xxpp
q
yyyy
q
xxxx
yx
yyyyxxxx
DDDDD
yxQ
2
22
2
22
2
22
2
22222
22
2222
22
Emittance andBetatron Matching
Dispersion andDispersionMatching
Injection Steering and Closed Orbit
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
Electric Quadrupole Electric Quadrupole Pick-upPick-up
Buffer AmplifiersSaturation - frequency mixingRadiation sensitive - close to beam
HybridVery high CMRR needed
Pick-up Buffer Hybrid Amplifier
SHVQ
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
What’s special about the What’s special about the PS pickup?PS pickup? Magnetic coupling!
Low impedance - no active electronics needed near beam (no saturation effects or radiation problems)
Can suppress the common mode signal by coupling to radial field component
Sum Hor Ver Quad
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
The Prototype Pick-upThe Prototype Pick-up Using a ceramic vacuum
chamber (old Booster spare) Vacuum reasons (no
feedthrus) Longitudinal impedance
(resistive layer screens the cavity, but lets the quadrupole signal thru)
Each loop signal goes thru a 1:15 current transformer directly into the hybrid (no impedance buffer)
Installed in the PS ring in the (last days of the) winter shut down 98/99
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
Data Acquisition and Data Acquisition and AnalysisAnalysis
Data is analysed primarily in time domainLHC beam: 2×4 booster bunches all coming from ‘different
machines’, thus each bunch has to be treated separatelyThe injection is a transient process
Pick-up Hybrid Amplifier
SHVQ
Scope
Pick-up/Wall current monitor
PC
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
Data treatmentData treatment Sum signal: Gaussian fit to find peak
current, bunch length and arrival time for each bunch passage.
Use knowledge of arrival time and bunch length to reduce the number of free parameters in the fit to the H, V, and Q signals (significantly reduces noise)
Spin-off Bunch synchronisation RF matching Coherent oscillations
Inclusion of known pick-up imperfections (ongoing)
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
LabView Application LabView Application ProgramProgram
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
Beam measurementsBeam measurements Beam envelope oscillations
due to betatron and dispersion mismatchStrong damping due to
space charge tune spread Beam envelope oscillations
due to coupling ‘Uncoupled’ beam injected
into a coupled machine
0 50 100 150 200Turn
-30
-20
-10
0
10
QH2mmL
0 50 100 150 200Turn
-40
-30
-20
-10
0
10
20
QH2mmL
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
An improved lab An improved lab prototypeprototype Metal sheets in the (electric)
symmetry planes for the quadrupole mode. Suppresses dipole and sum
signal Improves the longitudinal
impedance Improvement of the pick-up
transformers in order to further enhance the high frequency CMRR (ongoing)
Simulations show that the coating resistance can be reduced to 2-3 (ZL ~ 1.5 )
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
Pick-up response to a wire antenna displaced along the horizontal axis
CMRR of single loop 40-60 dB (improvements for HF underway)
Lab measurementsLab measurements
-7.5 -5 -2.5 0 2.5 5 7.5 10PositionHmmL
-0.00015
-0.0001
-0.00005
0
0.00005
0.0001
0.00015
0.0002
la
ng
iSHbra.
st
inuL
- 2.04958´ 10- 6 +0.0000149907 x - 3.52252´ 10- 7 x2
-7.5 -5 -2.5 0 2.5 5 7.5 10PositionHmmL
-0.00015
-0.0001
-0.00005
0
0.00005
0.0001
0.00015
0.0002
la
ng
iSHbra.
st
inuL
4.38422´ 10- 7 +0.0000128831 x+3.21346´ 10- 7 x2
-7.5 -5 -2.5 0 2.5 5 7.5 10PositionHmmL
-0.00015
-0.0001
-0.00005
0
0.00005
0.0001
0.00015
0.0002
la
ng
iSHbra.
st
in
uL
- 1.72278´ 10- 7 - 0.0000125502 x+3.08264´ 10- 7 x2
-7.5 -5 -2.5 0 2.5 5 7.5 10PositionHmmL
-0.00015
-0.0001
-0.00005
0
0.00005
0.0001
0.00015
0.0002
la
ng
iSHbra.
st
in
uL
9.52369´ 10- 7 - 0.0000143045 x - 3.33418´ 10- 7 x2
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
An ‘ideal’ detection An ‘ideal’ detection systemsystem Two complementary pick-ups!
Can detect all combinations of horizontal and vertical mismatch, independent of tune (and without FFT analysis)
Can (roughly) measure transverse emittances on a turn-by-turn basis Single shot accuracy ~0.5m
(statistical, main systematics from , ~10%) with present pick-up system
Possible in the PS ring, from point of view of space and beam optics
~
n
/2
H<<V
V<<H
3/12/99 PPC - The Quadrupole Pick-up in the CPS - A. Jansson
SummarySummary
Quadrupole pick-ups can be used as a ‘watchdogs’ for detecting (and correcting) Betatron and dispersion
matching Injection steering RF matching Bunch synchronisation
Two quadrupole pick-ups can measure the emittance!
In addition, quadrupole pick-ups are useful to study things like Space charge effects
(detuning and damping) Coupling and matching of
coupled machines …
Our experience with the new quadrupole pick-up design is good. Further improvements are foreseen for the final version (both HW & SW).
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