Transverse Emittance Scanning Techniques at

ISISScott Lawrie

Emittance Measurements at ISIS

• Transverse emittance only measured at low energy

• Slit-slit scanners on ISIS LEBT• Slit-slit & pepperpot on ISDR• Additional laser emittance

measurements to be used on FETS

Slit-Slit Technique

ISIS LEBT Emittance Scanners

Installation of RFQ at ISIS, 2004

Ion Source Development Rig (ISDR) Emittance Scanners

The Slit-Slit Scanners

The Slit-Slit Scanners

0.25 x 60 mm position

sampling slit

0.08 x 60 mm slit and

Faraday cup

500 V Electron Suppressor

The Slit-Slit Scanners

Main Arm Stepper Motor

Slit and Cup Stepper Motors

Vacuum Resistance

Springs

Data Output Cable

Electron Suppressor

Voltage

The Slit-Slit Scanners

Main Arm Travel

Distance= 18 cm

Slit and Cup Travel Distance

= 6.4 cm

The Slit-Slit Scanners• Maximum position resolution 0.25 mm• Maximum angle resolution 4 mRad• Maximum time sample rate 2 µs• Scan can be split into two• Total position scan range 120 mm• Scanning time 5 mins (0.5 mm res.) or

10 mins (0.25 mm res.) per arm• Soft interlock ensures fully parked

before starting scan

Example Scan

Slit-Slit Scanner Software

Slit-Slit Scanner Software

• Multiple document interface in C#• Fully multi-threaded throughout• Save and retrieve scans for

comparison• Communicate with scanning arms• Hardware independent• Automatic or manual axis scaling• Simple scanning parameter setup

Slit-Slit Scanner Software• Suit of data analysis tools

– Beam current vs. time plot– Beam integral profile plot– Highlight beam wings and haloes– Background noise drift and bias removal– Repair broken pixels

• Thorough emittance calculations– Threshold cut method– SCUBEEx method

Pepperpot Technique

The ISDR Pepperpot

The ISDR Pepperpot

Light-tight bellows

Beam shutter control

10 µm accuracy digital vernier.Longitudinal

movement up to 700 mm

PCO 2000 Camera• Temperature controlled CCD• 2048 x 2048 pixel• f / 2.8 shutter• 0.5µs sample rate• FireWire output

The ISDR Pepperpot

Pepperpot head mount

Quartz scintillator

glass

Window

Moveable stage and

camera mount

The ISDR Pepperpot

Tungsten mask

• 50 µm holes• 3 mm pitch• 41 x 41 arrayCopper grid

• 2 mm holes• 10 mm drift length• Prevents beamlet crossing• Improves cooling

The ISDR Pepperpot• Per spot resolution 3 mm• Per pixel resolution 0.07 mm• Maximum angle resolution 7 mRad• Imaging area 120 x 120 mm²• Calibration image taken for each scintillation

image• Match each beam spot with hole it came

from to determine divergence• Correct for skew etc

Example ImagesCalibration Scintillation Spots

Pepperpot Analysis Software

Pepperpot Analysis Software• Image calibration• Skew correction• Display various plots

– Spot Image of profile– Quiver plot of profile– Histogram of phase space… etc

• Calculate emittance• Export particle positions to GPT

Comparison of Results

εH = 0.80 norm. π mm mRad εH = 0.82 norm. π mm mRad

εV = 0.35 norm. π mm mRad εH = 0.32 norm. π mm mRad

Comparison of Results

Slit-Slit Pepperpot

Pros

• High resolution• Emittance plot is ready made• Standard analysis techniques• Small errors in emittance

• Very fast data capture time• Longitudinal motion• Simple hardware positioning• Horz. & vert. phase space AND profile measured together

Cons

• Slow to gather data• Horz. & vert. scans decoupled• Fixed longitudinal position• Complicated hardware control

• Lower resolution• Need to extract phase space• More difficult data analysis• Limited scintillator lifetime

Comparison of Results

Photodetachment Technique

Future Emittance Measurements

• Novel laser wire emittance scanner– Non-destructive– Can use even with high beam power

• Laser acts as “slit”, scintillator as “grid”• Profiles taken at various positions• Combine using Maximum Entropy

Technique (MENT) to calculate emittance

Summary

• Transverse emittance well understood for beam from the ISIS ion source

• Two highly successful methods• Comprehensive data analysis software• Calculated emittance values agree• Continual improvement and

development of new techniques

Questions?

Scott LawrieISIS, Rutherford Appleton Laboratory, STFC, UK

scott.lawrie@stfc.ac.uk

Additional Slides

Slit-Slit Diagnostics

Beam current monitorBeam profile monitor

Enhance Beam Halo Contrast

3% cut 7% cut

Contrast off, 0% cut Contrast on, 0% cut

Background Drift RemovalRaw data:

Data with fixed drift:

Fix Broken Pixels/ColumnsRaw data Shifted Pixels Repaired

Pepperpot Plots

Scintillator Material• Tested various scintillators for:

– Light output intensity– Light decay time– Lifetime of material when exposed to beam

• Tried:– P46, P47, P43 good light output, short lives

– LYSO, BSCO, PbWO4, CdWO4 poor lifetimes

– Ruby, YAG:Ce Promising, but no big sheets

• Settled for pure quartz

P46 Phosphor DamageMulti-spot damage

(front view)

Single spot damage(front view)

Single spot damage(side view)

Spot intensity

Plastic Scintillator DamageMulti-spot damage

(front view) Single spot damage(front view)

Single spot damage(side view)

Spot intensity

SCUBEEx Emittance MethodHalf-axis product = 50

[Ref: Martin Stockli, Rod Keller, Alan Letchford et al,AIP Conference Proceedings, Vol. 639, pp 135-159 (2002)]

SCUBEEx Emittance MethodHalf-axis product = 200

SCUBEEx Emittance MethodHalf-axis product = 500

SCUBEEx Emittance MethodHalf-axis product = 1000

SCUBEEx Emittance MethodHalf-axis product = 5000

SCUBEEx Emittance Method

Normalised Horizontal emittance = 0.31 ± 0.01 π mm mRad

(Re: Emittance calculated using 10% threshold = 0.35 π mm mRad)

SCUBEEx Emittance Method

SCUBEEx Emittance vs. Time80 µs

90 µs

150 µs

300 µs