Transverse Emittance Scanning Techniques at ISIS
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Transcript of Transverse Emittance Scanning Techniques at ISIS
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
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