status report on mk.ii pepperpot
DESCRIPTION
Status Report on Mk.II Pepperpot. Simon Jolly Imperial College 13 th June 2007. Pepperpot Components. Pepperpot head: Tungsten intercepting screen, 50 m m holes on 3mm pitch in 41x41 array. Tungsten sandwiched between 2mm/10mm copper support plates. Quartz scintillator images beamlets. - PowerPoint PPT PresentationTRANSCRIPT
Status Report on Mk.II Pepperpot
Simon Jolly
Imperial College
13th June 2007
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Pepperpot Components• Pepperpot head:
– Tungsten intercepting screen, 50m 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.
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Vacuum bellows
Camera
Moving rod
Shutter
Mounting flange
Pepperpot head
Bellows
Tungsten mesh
Beam profile head
FETS Pepperpot Design
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Pepperpot Installation
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“0 mm” position of pepperpot head is 57 mm downstream of cold box exit. 458 mm dynamic range means “300 mm” position is approximately 20 mm upstream of slit-slit scanners.
57 mm
Pepperpot Location Inside Ion Source
458 mm 100 mm
Measurements taken at 100 mm intervals.
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Mk.II Pepperpot Recent Improvements
• Completed:– Multiple calibration markings on pepperpot and profile
heads.– Sliding camera mount to improve resolution.– Larger, permanent camera-bellows mount (not
cardboard!).• To do:
– Background light replacement to improve calibration.– Support for new bellows mount.– Clamp to support sliding mount to prevent it toppling
forward.– Install new components: Tuesday 16th June?
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Pepperpot Data ImageRaw data Calibration image
Colour enhanced raw data image, 60 x 60 mm2.
Calibration image: use corners of 9 mm x 9 mm square on copper plate to give image scaling, tilt and spot spacing.
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Pepperpot Emittance Extraction
Pepperpot image spots: hole positions (blue) and beam spots (red)
Emittance profiles
Y
X
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13 kV Extract: 0 mm
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13 kV Extract: 100 mm
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13 kV Extract: 200 mm
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13 kV Extract: 300 mm
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Position Variation for 13 kV Extract
0 mm
100 mm
200 mm
300 mm
x = 1.36y = 1.47 mm mrad
x = 1.82y = 1.96 mm mrad
x = 1.65y = 1.78 mm mrad
x = 1.90y = 2.04 mm mrad
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Results of Position Variation
• Behaviour as expected: steady expansion in beam size along the beam axis.
• Emittances show no obvious nonlinearities; increases may be a result of space charge effects.
• Level of space charge compensation needs to be investigated with beam dynamics simulations.
• Flat top and bottom of the beam profile are likely due to collimation occurring upstream of the ion source exit.
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6 kV Extract: 0 mm
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9 kV Extract: 0 mm
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13 kV Extract: 0 mm
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17 kV Extract: 0 mm
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Variation of Extract Voltage at 0 mm
6 kV
9 kV
13 kV
17 kV
x = 0.25y = 0.77 mm mrad
x = 1.36y = 1.47 mm mrad
x = 0.74y = 1.14 mm mrad
x = 2.02y = 1.92 mm mrad
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Results of Extract Variation• Distinct change in beam shape, density distribution and emittance:
– 6 kV shows strong asymmetric divergence in both planes.– 9 kV shows mostly vertical expansion.– 13 kV is nearly symmetric and slightly collimated.– 17 kV dominated by collimation.
• A number of factors contribute to changes:– Upstream collimation.– Change in extract potential: changes shape of field within extract
region, and affects shape of discharge plasma.– Increase in extract potential also requires change in 90° sector
magnet current: change focussing effect of fringe fields.– Decrease in post-acceleration voltage means transverse
focussing from fringe fields within post-acceleration gap will change.
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Results Summary
Extract (kV)
Current (mA)
Z (mm) Beam size ( mm mrad)
x (mm) y (mm) x,rms y,rms
± 1 ± 1 ± 0.1 ± 3 ± 5 %
6 13 0 18 33 0.25 0.77
9 22 0 27 63 0.74 1.14
13 34 0 51 60 1.36 1.47
13 34 100 57 72 1.65 1.78
13 34 200 69 87 1.82 1.96
13 34 300 78 102 1.90 2.04
17 36 0 57 63 2.02 1.92
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Scintillator Measurements
5 kV Ext 5.5 kV Ext 6 kV Ext 6.5 kV Ext
7 kV Ext 8 kV Ext 9 kV Ext 11 kV Ext
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Scintillator/Pepperpot Comparison: 6 kV
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Scintillator/Pepperpot Comparison: 9 kV
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Conclusions
• First results already promising.• Detailed research program under discussion:
start with categorising scintillator.• Clear comparison between scintillator and
pepperpot measurements: calibration markings should allow precise correlation between the two.
• Quality of results should improve with latest modifications.
• Lots of data to take…