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Pepperpot Emittance Measurements of the FETS Ion Source

Pepperpot Emittance Measurements of the FETS Ion Source. Simon Jolly Imperial College 3 rd October 2007. The Pepperpot Emittance Scanner. Current slit-slit scanners give high resolution emittance measurements, but at fixed z-position, with x and y emittance uncorrelated.

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Pepperpot Emittance Measurements of the FETS Ion Source

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  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. Simon Jolly, Imperial College

  3. 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 Simon Jolly, Imperial College

  4. 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. Simon Jolly, Imperial College

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

  6. Pepperpot Installation Simon Jolly, Imperial College

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

  8. 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. Simon Jolly, Imperial College

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

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

  12. Pepperpot/Profile Comparison Simon Jolly, Imperial College

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

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

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

  18. Ce-Quartz Decay: 1000 Images Simon Jolly, Imperial College

  19. 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. Simon Jolly, Imperial College

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