1. Pepperpot Emittance Measurements of the FETS Ion Source
Simon Jolly
Imperial College
3rd October 2007

2. The Pepperpot Emittance Scanner
Current slit-slit scanners give high resolution emittance measurements, but at fixed z-position, with x and y emittance uncorrelated.
Correlated, 4-D profile (x, y, x’, y’) required for accurate simulations.
Pepperpot reduces resolution to make correlated 4-D measurement.
Moving stage allows measurement at different z-locations: space charge information.
Possible to make time-resloved measurements within a single pulse.
Added bonus: make high resolution x-y profile measurements.
3/10/07
Simon Jolly, Imperial College

3. Simon Jolly, Imperial College
Pepperpot Principle
Beam segmented by tungsten screen.
Beamlets drift ~10mm before producing image on quartz screen.
Copper block prevents beamlets from overlapping and provides cooling.
CCD camera records image of light spots.
Calculate emittance from spot distribution.
Quartz screen
Copper block
Fast CCD Camera
H- Ion Beam
Tungsten screen
H- Beamlets
3/10/07
Simon Jolly, Imperial College

4. Simon Jolly, Imperial College
Pepperpot Components
Pepperpot head:
Tungsten intercepting screen, 50mm holes on 3mm pitch in 41x41 array.
Tungsten sandwiched between 2mm/10mm copper support plates.
Quartz scintillator images beamlets.
Camera system:
PCO 2000 camera with 2048 x 2048 pixel, 15.3 x 15.6 mm CCD.
Firewire connection to PC.
105 mm Micro-Nikkor macro lens.
Bellows maintains light tight path from vacuum window to camera.
Main support:
Head and camera mounted at either end of 1100 mm linear shift mechanism, with 700 mm stroke.
All mounted to single 400 mm diameter vacuum flange.
3/10/07
Simon Jolly, Imperial College

5. Simon Jolly, Imperial College
FETS Pepperpot Design
Beam profile head
Tungsten mesh
Pepperpot head
Shutter
Bellows
Camera
Moving rod
Vacuum bellows
Mounting flange
3/10/07
Simon Jolly, Imperial College

6. Pepperpot Installation
3/10/07
Simon Jolly, Imperial College

7. ISDR Diagnostics X and Y Slit-Slit Emittance Scanners
Buffer Gas Delivery System
Movable Scintillator with Interchangeable Pepperpot or Profile Head
Beam Current Toriod
Diagnostic Dipole
Beam Shutter
Diagnostics Vessel
3/10/07
Simon Jolly, Imperial College

8. Simon Jolly, Imperial College
Pepperpot Data Image
Raw data
Calibration image
Colour enhanced raw data image, 60 x 60 mm2.
Calibration image: use corners of 126 x 126 mm square on copper plate to give image scaling, tilt and spot spacing.
3/10/07
Simon Jolly, Imperial College

9. Pepperpot Emittance Extraction
Emittance profiles X Y
Pepperpot image spots: hole positions (blue) and beam spots (red)
3/10/07
Simon Jolly, Imperial College

10. Pepperpot GUI and Data Analysis
3/10/07
Simon Jolly, Imperial College

11. Position Variation for 13 kV Extract
0 mm
200 mm
ex = 1.36
ey = 1.47
p mm mrad
ex = 1.82
ey = 1.96
p mm mrad
100 mm
300 mm
ex = 1.65
ey = 1.78
p mm mrad
ex = 1.90
ey = 2.04
p mm mrad
3/10/07
Simon Jolly, Imperial College

12. Pepperpot/Profile Comparison
3/10/07
Simon Jolly, Imperial College

13. Pepperpot vs. Slit-Slit: 11kV X Emittance
0.39 p mm mrad
3/10/07
Simon Jolly, Imperial College

14. Pepperpot vs. Slit-Slit: 11kV Y Emittance
0.45 p mm mrad
3/10/07
Simon Jolly, Imperial College

15. Emittance Cut Optimisation
As with Slit-Slit scanner, pepperpot emittance measurement is sensitive to cut level.
Have to impose some sort of cut due to inherent 100 count noise from camera and background noise.
Need to optimise cut level to give consistent emittance measurement.
3/10/07
Simon Jolly, Imperial College

16. Simon Jolly, Imperial College
Pepperpot 11kV: 119/250 Cut
119 cut
250 cut
3/10/07
Simon Jolly, Imperial College

17. Scintillator Problems
Pepperpot rapidly became “scintillator destruction rig”.
Scintillator requirements:
Fast (down to 500ns exposure).
High light output.
Survives beam (<1 micron stopping distance).
High energy density from Bragg peak causes severe damage.
Finally chose Ce-Quartz.
3/10/07
Simon Jolly, Imperial College

18. Ce-Quartz Decay: 1000 Images
3/10/07
Simon Jolly, Imperial College

19. Simon Jolly, Imperial College
Conclusions
2-D profiles with high resolution (70 mm)
Medium resolved 4-D emittance measurements (3 mm, 7 mrad).
Both data can be combined to produce 4-D data with high resolution.
Clear correlation between pepperpot, profile and slit-slit emittance measurements.
Emittance measurements at different z-positions allow investigation of space charge forces.
Able to output data into GPT and LINTRA simulations.
3/10/07
Simon Jolly, Imperial College