laser-based beam diagnostics for the ral front end test stand

Laser-based Beam Diagnostics for the RAL Front End Test Stand

David Leedavid.a.lee@imperial.ac.uk

28.01.2009

David Lee • 28/01/2009

Outline

• The Front End Test Stand (FETS)• Beam diagnostics

– Beam profile measurements– Non-intrusive beam diagnostics

• Laser-based H− diagnostics

• FETS laser profile monitor• Conclusion

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 1

The Front End Test Stand

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 2 David Lee • 28/01/2009

David Lee • 28/01/2009

The Front End Test Stand

Magnetic LEBT

RFQ

MEBT and chopper

H− ion source

Laser profile monitor

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 3

Beam dump and laseremittance measurementupstream (not shown)

David Lee • 28/01/2009

Neutrino Factory

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 4

David Lee • 28/01/2009

Neutrino Factory

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 4

David Lee • 28/01/2009

Status

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 5

David Lee • 28/01/2009

Status

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 5

David Lee • 28/01/2009

Status

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 5

David Lee • 28/01/2009

Status

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 5

Beam Diagnostics

David Lee • 28/01/2009Laser-based Beam Diagnostics for the RAL Front End Test Stand • 6

David Lee • 28/01/2009

Beam Profile Measurements

• Why are beam profile measurements of interest?– First half of the beam emittance– Gives information about the charge density

• And so the beam’s self field / space charge

– Will the beam fit through the beam pipe?– What is the beam halo like?– …

• How are they typically done?– Scintillator – Wire scanner– …

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 7

David Lee • 28/01/2009

Non-intrusive diagnostics

• Allows for online monitoring of the beam– Keeps users happy

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 8

David Lee • 28/01/2009

Non-intrusive diagnostics

• Allows for online monitoring of the beam– Keeps users happy

• Beam dynamics not affected by the instrument– Keeps accelerator group happy

RGIE spectrum (beam potential distribution)depending on position of emittance scanner

W / eV

dl’

/ d

W [

μA

/ (

eV

m)]

Residual gas ionenergy analyser

Ion source

0V

200V

0.365T 0.406T Beam dump0V

Allison scannerin / out

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 8

David Lee • 28/01/2009

Non-intrusive diagnostics

• Allows for online monitoring of the beam– Keeps users happy

• Beam dynamics not affected by the instrument• Prevents the beam from damaging the instrument

– Keeps accelerator group happy

Plastic RubyP46

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 8

David Lee • 28/01/2009

Ionisation Cross Section

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 9

David Lee • 28/01/2009

Ionisation Cross Section

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 9

David Lee • 28/01/2009

• To measure– Beam profiles– Longitudinal emittances

use photo-detached electrons

Laser-based H− diagnostics

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 10

David Lee • 28/01/2009

• To measure– Beam profiles– Longitudinal emittances

use photo-detached electrons

Photo-ionise someof the H- ions

Separate species usinga dipole magnet

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Collect the detached electrons

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Laser-based H− diagnostics

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 10

David Lee • 28/01/2009

Photo-ionise someof the H- ions

Separate species usinga dipole magnet

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−−

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− −

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−−

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Collect the detached electrons

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Laser-based H− diagnostics

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 10

David Lee • 28/01/2009

Photo-ionise someof the H- ions

Separate species usinga dipole magnet

−

−−

−

−

−

− −

−−−

−

−

−−

−

−

−

−

−

−

−−

Collect the detached electrons

−−

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−

−

−

Laser-based H− diagnostics

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 10

David Lee • 28/01/2009

Photo-ionise someof the H- ions

Separate species usinga dipole magnet

−

−−

−

−

−

− −

−−−

−

−

−−

−

−

−

−

−

−

−−

Collect the detached electrons

−−

−

−

−

−

−

Laser-based H− diagnostics

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 10

David Lee • 28/01/2009

Photo-ionise someof the H- ions

Separate species usinga dipole magnet

−

−−

−

−

−

− −

−−−

−

−

−−

−

−

−

−

−

−

−−

Collect the detached electrons

−−

−

−

−

−

−

Laser-based H− diagnostics

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 10

David Lee • 28/01/2009

Photo-ionise someof the H- ions

Separate species usinga dipole magnet

−

−−

−

−

−

− −

−−−

−

−

−−

−

−

−

−

−

−

−−

Collect the detached electrons

−−

−

−

−

−

−

Laser-based H− diagnostics

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 10

David Lee • 28/01/2009

• To measure– Transverse emittances

use photo-ionised neutrals

Laser-based H− diagnostics

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 11

David Lee • 28/01/2009

• To measure– Transverse emittances

use photo-ionised neutrals

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−

− −

−−

−

−

Laser-based H− diagnostics

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− −

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Use a dipole to separate out the particles neutralised by residual gas interactions

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 11

David Lee • 28/01/2009

• To measure– Transverse emittances

use photo-ionised neutrals

Photo-ionise some of the H- ions in the dipole

Residual gasneutrals

−

−

− −

−−

−

−

Photo-ionised neutrals

Laser-based H− diagnostics

−

−

−

−

−

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 11

David Lee • 28/01/2009

• To measure– Transverse emittances

use photo-ionised neutrals

Photo-ionise some of the H- ions in the dipole

−

−

− −

−−

−

−

Image with scintillator and CCD

CCD

Laser-based H− diagnostics

−

−

−

−

−

Residual gasneutrals

Photo-ionised neutrals

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 11

David Lee • 28/01/2009

Photo-ionise some of the H- ions in the dipole

−

−

− −

−−

−

−

CCD

Laser-based H− diagnostics

−

−

−

−

−

Photo-ionised neutrals

Image with scintillator and CCD

Residual gasneutrals

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 11

The Front End Test StandLaser Profile Monitor

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 12 David Lee • 28/01/2009

David Lee • 28/01/2009

The Benefit of Multiple (>2) Projections

David Lee • 28/01/2009Laser-based Beam Diagnostics for the RAL Front End Test Stand • 13

David Lee • 28/01/2009

The Benefit of Multiple (>2) Projections

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 13

David Lee • 28/01/2009

The Benefit of Multiple (>2) Projections

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 13

David Lee • 28/01/2009

The Benefit of Multiple (>2) Projections

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 13

David Lee • 28/01/2009

Laser-scanning setup

• To get multiple projections, need to be able to pass laser through beam at variety of angles

• To do this, use movable mirrors mounted in vacuum vessel

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 14

David Lee • 28/01/2009

Laser-scanning setup

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 15

David Lee • 28/01/2009

Laser-scanning setup

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 15

David Lee • 28/01/2009

Optics

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 16

A simple, one lens setup will be used to begin with

David Lee • 28/01/2009

Optics

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 17

David Lee • 28/01/2009

The Detector

FaradayCup

Magnet

Copperaccelerating

sheath

H−, H0

Electrons

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 18

David Lee • 28/01/2009

The Detector

Beamdirection

• Constructed here in the workshop

• Compact; the whole assembly is~80x100x250 mm

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 19

David Lee • 28/01/2009

Simulations

• Detector’s E and B fields simulated using a electromagnetic finite element program – CST EM Studio

• Particle tracking was performed by the General Particle Tracer package

• Input distribution from a pepperpot correlated emittance measurement of the ion source

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 20

David Lee • 28/01/2009

Simulations

FaradayCup

Magnet yoke

Copperacceleratingsheath

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 21

David Lee • 28/01/2009

Dipole Field Map

• To confirm the simulation results the dipole had its field (bending component; By) mapped

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 22

David Lee • 28/01/2009

Dipole Field Map

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 23

David Lee • 28/01/2009

Dipole Field Map

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 24

David Lee • 28/01/2009

Longitudinal Acceptance

• Electrons from residual gas interactions form a background to our measurement– Problem made worse by proximity to ion source

• 20 ml per minute of hydrogen gas

• To reduce this background, the longitudinal acceptance of the detector can be reduced byintroducing an additional electrode

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 25

David Lee • 28/01/2009

Longitudinal Acceptance

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 26

David Lee • 28/01/2009

Longitudinal Acceptance

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 26

David Lee • 28/01/2009

Longitudinal Acceptance

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 26

David Lee • 28/01/2009

Longitudinal Acceptance

-500V

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 26

David Lee • 28/01/2009

Longitudinal Acceptance

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 26

David Lee • 28/01/2009

Longitudinal Acceptance

-500V

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 26

David Lee • 28/01/2009

Longitudinal Acceptance

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 26

David Lee • 28/01/2009

Longitudinal Acceptance

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 27

David Lee • 28/01/2009

Readout Electronics

• Microprocessor controlled integrate and hold ADC with serial output to PC

• LabVIEW-based DAQ

• In the process of testing and fine-tuning production version

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 28

David Lee • 28/01/2009

Readout Electronics

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 29

David Lee • 28/01/2009

Reconstruction

• Currently envisaged that the profiles will be reconstructed using the Algebraic Reconstruction Technique (ART) algorithm– Maximum entropy (MENT) also under consideration

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 30

Original Profile Reconstructed Profile

David Lee • 28/01/2009

Conclusion

• A novel laser-based beam diagnostic that is able to measure the full profile of the FETS H− beam has been designed and constructed

• It is currently being installed at RAL• And should be ready to make measurements on

the first beam in a few weeks time

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 31

Spare Slides

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 32

David Lee • 28/01/2009

ISIS Upgrades

ISIS

(0.24 MW)

Diamond

3 GeV RCS

(1 MW)

400-800 MeV Linac

(2-5 MW)

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 33

David Lee • 28/01/2009

For scale: CERN

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 34

David Lee • 28/01/2009

For scale: CERN

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 34

David Lee • 28/01/2009

For scale: CERN

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 34

David Lee • 28/01/2009

For scale: CERN

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 34

David Lee • 28/01/2009

H− Injection

H− from Linac

Circulating protons

Stripping foil

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 35

David Lee • 28/01/2009

FETS Ion Source

Mounting Flange 10mm

Mica

Copper Spacer

Ceramic

H- Ion Beam Extract Electrode

Cathode

Anode

Penning Pole Pieces

Discharge Region

Aperture Plate

Source Body

53.7mm

35kV

17kV

PlatformGround

Platform DC Power Supply

Pulsed Extract Power Supply

Post Extraction

Acceleration Gap

Laboratory Ground

Extraction Electrode, Coldbox and Analysing Magnet all Pulsed

35keV H- Beam

+-

+-

18kV

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 36

David Lee • 28/01/2009

FETS LEBT

• Matches beam from the ion source to the RFQ• 3 solenoid construction• Solenoids and their power

supplies complete• Beam pipe design complete

D DDD SS S

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 37

David Lee • 28/01/2009

Solenoid Focussing

• Second order focussing– Field gradient starts rotation

of particles about axis

– This rotation then produces a focussing force towards the axis

F, v, B

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 38

David Lee • 28/01/2009

FETS RFQ

• Cold model complete– RF tests underway to verify

simulation• mostly complete

• Mechanical design study starting– Integrated with simulation

work– Lots to consider

• How to manufacture

• Cooling

• …

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 39

David Lee • 28/01/2009Simon Jolly, Imperial College

RFQ Focussing

• RF field causes positive / negative charges on pairs of vanes.

• Since field varies with time, alternate focussing / defocussing mimics a FODO lattice.

Standard Quad

RFQ E-field

RFQ vane tips

David Lee • 28/01/2009Simon Jolly, Imperial College

RFQ Acceleration/Bunching

• RFQ vane tips modulated longitudinally.– Vane tip modulations produce longitudinal field:

acceleration and bunching.

Single vane

= distance moved by particle in one oscillation

+

-

Alternate modulation gives acceleration

David Lee • 28/01/2009

FETS MEBT/Chopper (I)

• Matching between RFQ and DTL• Houses beam chopper to remove some bunches

of the beam

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 42

David Lee • 28/01/2009

FETS MEBT/Chopper (II)

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 43

David Lee • 28/01/2009

Laser-based e± diagnostics

http://www.pp.rhul.ac.uk/~lbbd/

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 44

David Lee • 28/01/2009

Laser Characterisation

• Need a compromise between– Having as high a resolution as possible

• Lots of bins in histogram

– But not having an over-focussed beam• That would distort the measurement

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 45

David Lee • 28/01/2009

H- profile comparison

Initial particle distribution H- distribution just past magnet

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 46

David Lee • 28/01/2009

H- phase space comparison

Initial particle distribution H- distribution just past magnet

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 47

David Lee • 28/01/2009

H- phase space comparison

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 48

David Lee • 28/01/2009

Residual gas interactions

• Assuming partial pressures of – H2: 5x10-3 Pa

– N2: 5x10-5 Pa

we loose ~2% of the beam per metre(or ~1.8x1013 ions per metre)

• So we need to minimise the fraction of these collected to minimise the background

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 49

David Lee • 28/01/2009

Stray fields

• The ion source dipole field leaks into the diagnostic vessel

• Scott Lawrie (RAL) has designed shielding for thisDeflections (with no E-field)– Average deflection: 3.88 mm (with B-field)– Average deflection: 0.0252 mm (no B-field)

• Deflections (with E-field)– Average deflection: 2.44 mm (with B-field)– Average deflection: 0.044 mm (no B-field)

• Shielding sufficient

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 50

David Lee • 28/01/2009

ART

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 51

David Lee • 28/01/2009

ART

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 52

David Lee • 28/01/2009

ART

Laser-based Beam Diagnostics for the RAL Front End Test Stand • 53