The Quadrupole Pick-up in the CPS -intro and progress report PPC 3 Dec 1999 A. Jansson

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


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


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'''')','(


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 ),(


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


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


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


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


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


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


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)


LabView Application LabView Application ProgramProgram


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


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 )


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


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


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).

Documents

The Quadrupole Pick-up in the CPS -intro and progress report PPC 3 Dec 1999 A. Jansson