lyon 2005 dipac lyon 2005 7 th dipac lyon june 2005ulrich raich cern ab/bdi instrumentation in...

DIPAC Lyon June 2005 Ulrich Raich CERN AB/BDI

Lyon 2005DIPAC Lyon 2005

7th

Instrumentation in small, low energy machines

Ulrich Raich

CERN AB-BDI



7th

The LHC

• The LHC is CERN’s flagship projectbut … it is not exactly a small, low energy machine!

• why start with the LHC?Dump line

Proton source

Proton Linac

Ion Linac

RFQ

RFQ

Duo PlasmatronProton source

Cyclotron resonanceIon source



7th

Luminosity

Quality factor of a collider: luminosity

n

b NkL

2

• Depends on kb: number of bunches

• N: number of particles per bunch

• εn: emittance

LEP was limited in energy by synchroton radiation

In LEP, due to Landau damping, the biggest machine was largely responsible for beam quality.

In LHC the injectors determine beam quality



7th Peculiarities of small machines

Particles have small magnetic rigidity BρParticles are easy to bend

Beam spot and angles are large (adiabatic damping)physical emittance shrinksfactor 1500 from 50MeV – 450 GeV

They need tight mesh of focusing magnets (leaves little space for instrumentation)

Space charge Energy deposition inintercepting matter is highFew instruments but large varietyParticle speed changes with acceleration

Photo GSI Darmstatt



7th

Uses of small machines

• Small machines:– Injectors for bigger machines– Test stands– Medical machines– Accelerators for industrial use (ion implantation, material tests)

even the Louvre has an accelerator– Accelerators at Universities or small research institutes



7th Intensity measurementsFaraday Cup

• Electrode: 1 mm stainless steel

• Only low energy particles can be measured

• Very low intensities (down to 1 pA) can be measured

• Creation of secondary electrons of low energy (below 20 eV)

• Repelling electrode with some 100 V polarisation voltage pushes secondary electrons back onto the electrode

Contributed by G. Molinari and V. Prieto



7th Repelling secondary electrons

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0.1 1 10 100 1000

Itotal vs. eV

90keV50keV30keV

I(µA)

V

• With increasing repelling voltage the electrons do not escape the Faraday Cup any more and the current measured stays stable.

• At 40V and above no decrease in the Cup current is observed any more



7th Measurements of ion charge-state distribution

Faraday Cup

slit

Spectrometer magnets

Scan of Bending magnet Current with extraction voltage 20.5kV -11/04/03 -JCh

-0.05

0

0.05

0.1

0.15

60 65 70 75 80 85 90 95 100

Bending Magnet Current (A)

Ave

rag

e C

urr

ent

fro

m

Far

ard

ay c

up

2 (

mA

)



7th

Current transformers

• Often very close to pulsing magnetic elements

• Needs good shielding• Long beam pulses from

ion sources (typical 100μs)

• Digitization of raw signal with digital integration is possible



7th

Magnetic shielding

Shield should extend along the vacuum chamber length > diameter of opening

Shield should be symmetrical to the beam axis

Air gaps must be avoided especially along the beam axis

Shield should have highest μ possible but should not saturate

monitor

Soft iron (μ1) Transformer steel (μ2)

Permalloy (μ3)



7th Calibration of AC current transformers

The transformer is calibrated with a very precise current source

The calibration signal is injected into a separate calibration winding

A calibration procedure executed before the running period

A calibration pulse before the beam pulse measured with the beam signal

Trace contributed by F. Lenardon



7th

• with the following constants:NA: Avogadro’s number

me and re: electron rest mass and classical electron radiusc: speed of light

• the following target material properties:ρ: material density

AT and ZT: the atomic mass and nuclear charge• and the particle properties:

Zp: particle chargeβ: the particles velocity and

Dependance on

Interaction of particles with intercepting matter

]2

[ln4 2222

2

222

I

cmZ

A

ZcmrN

dx

dE ep

T

TeeA

21

2pZ

1

50

0.1 0.01 1

2

5

10

20

]/

[2cmg

MeV

dx

dE

gas

solid

Ekin[GeV]

10 100 1000



7th

Screen Tests

Penetration depth of ions at 4 MeV/u: <10µm

Particle energy is deposited in very small volume

Heat load and electric charging becomes a problem

Several screen materials tested

T. Lefevre, this conference



7th Test for resistance against heat-shock

-10 0 10 20 30 40

0.1

1

10

100

1000

10000

Test start +2min +3min +1h30 +3h

Ligh

t int

ensi

ty (

u.a.

)

Y (mm)

-10 0 10 20 30

10000

20000

30000

40000

50000

Start 90C (30min) 450C (2h30min) 585C (3h15min) 720C (4h)

Lig

ht

inte

nsity (

u.a

.)

Y (mm)

Material

g/cm3

cp at 20ºC

J/gK

k at 100ºC

W/mK

Tmax

ºC

R at 400 ºC

Ω.cm

Al2O3 3.9 0.9 30 1600 1012

ZrO2 6 0.4 2 1200 103

BN 2 1.6 35 2400 1014

Better for electrical conductivity (>400ºC)

Better for thermal properties(higher conductivity, higher heat capacity)

Use as reference

question



7th

Wire Scanners

A thin wire is quickly moved across the beamSecondary particle shower is detected outside the vacuum chamberon a scintillator/photo-multiplier assembly Position and photo-multiplier signal are recorded simultaneously



7th Problems at low energy

• Secondary particle shower intensity in dependence of primary beam energy



7th Wire scanners and partially stripped ions

-2 -1 0 1 2

Beam centeredreached at t0

Beam edgereached

time [ms]

Bea

m c

urre

nt [

arb.

units

]

Partially stripped ions loose electronswhen interacting with the wire

The beam is lost

Can measure amplitude distributionhowever



7th Transforming angular distribution to profile

• A slit produces a vertical slice in transverse phase space

• Moving the slit scans the phase space

• When moving through a drift space the angles don’t change (horizontal move in phase space)

• When moving through a quadrupole the position does not change but the angle does (vertical move in phase space)

x’

xslit

Influence of a quadrupole

slit

x’

x

x’

x

Influence of a drift space

slit



7th

The Slit Method

3d plot from P. Forck



7th Single pulse emittance measurement

Kickers

slit

SEMgrid

Every 100 nsa new profile



7th Result of single pulse emittance measurement



7th

Multi-slit measurement

Needs high resolution profile detector

Must make surethat profilesdont overlap

beam

Scintillator + TV + frame grabberoften used as profile detector

Very old idea, was used with photographic plates



7th

Pepperpot

Uses small holes instead of slits

Measures horizontal and vertical emittance in a single shot

Photo P. Forck



7th

Longitudinal emittance

E

φ

Spectrometer magnet

kicker

slit

buncher

Spectrometer magnet

kicker

SEMgrid

• Spectrometer transforms energies into positions• Buncher transforms time into Energy



7th

The End

• Thanks for your attention

lyon 2005 dipac lyon 2005 7 th dipac lyon june 2005ulrich raich cern ab/bdi instrumentation in...

Documents

th dipac lyon

ulrich raich cern abbdi

beam quality slide

possible slide

lenardon slide

prieto slide

small machines small

intercepting matter