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…