AWAKE Electron Spectrometer
Simon Jolly6th December 2013
Spectrometer Specifications
• Wakefield accelerated electrons ejected collinear with proton beam: need to separate the 2 and measure energy of electron beam only.
• Must be able to resolve energy spread as well as energy: spectrometer must accept a range of energies, probably 0-5 GeV.
• Current conceptual layout:– Dipole mounted ~2 m downstream of plasma exit
induces dispersion in electron beam.– Scintillator screen 1 m downstream of dipole
intercepts electron beam ONLY.– Dispersion gives energy-dependent position spread
on screen.– Scintillator imaged by intensified CCD camera
viewing upstream face of scintillator screen.
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2 GeV Beam, 1.86 T Field
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2 GeV Beam, 1.86 T Field
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2 GeV Beam, 1.86 T Field
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2 GeV Beam, 1.86 T Field
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2 GeV Beam, 1.86 T Field
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2 GeV Beam, 1.86 T Field
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AWAKE Spectrometer Area
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Spectrometer Layout
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Camera
Scintillator Screen
CERN MBPS dipole
Protons
Electrons + Protons
Current Progress
• Reconstruction software shows we can resolve energy spread in electron beam given reasonable intensity pattern on screen.
• Current work progressing on several fronts:– Scintillator screen light output.– Vacuum layout (protons inside, DAQ
outside).– Optimum experimental geometry.– Alternative screen technologies.
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Scintillator Screen• Default scintillator choice is Lanex:
• Manufactured by Kodak.• Used in Medical Physics as X-ray phosphor for imaging.• Gd2O2S:Tb – Gadolinium sensitiser, Terbium dopant
activator/wavelength shifter.• Phosphor grains on reflective backing.• Properties don’t seem to be well documented/studied…
• Need to simulate light production (photons per MeV conversion efficiency) to ensure we have enough photons emitted in direction of camera.
• Is this the correct scintillator for our purposes?
• We care about:• Light output.• Resolution• Radiation hardness.• Area.
• We don’t care about:• Speed.
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GadOx: Geant4 Photons (J. Goodhand)
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And Now:A Scintillator
Interlude.
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A Scinterludeyoutu.be/gaI6kBVyu00
MBPS Magnet
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MBPS Magnet: Good Field Region?
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300 mm 1000 mm
Spectrometer Layout
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Spectrometer + Beam Dump
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Beam Dump
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AWAKE Spectrometer Area (1)
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AWAKE Spectrometer Area (2)
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AWAKE Spectrometer Area (3)
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Spectrometer Camera View (1)
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Spectrometer Camera View (2)
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Spectrometer Camera View (3)
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No Vacuum
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Vacuum Vessel (1)
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Vacuum Vessel (2)
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Vacuum Window
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Vacuum Window: Fresnel Lens
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No Vacuum
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Windowed Beampipe (1)
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Windowed Beampipe (2)
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Reverse Geometry
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Reverse Geometry: Beam Dump
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Reverse Geometry: Camera Position
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Reverse Geometry: Vacuum Vessel
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Light Tight Vessel
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Off-Axis Camera + Focussing Mirror
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Off-Axis Camera: CNGS Tunnel
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Spectrometer Status
• Preliminary Geant4 scintillator results encouraging:– ~100,000 photons into camera without additional
optics.– Some results need more investigation…
• Work ongoing to optimise experimental layout:– We need a vacuum vessel for protons, but what
about electrons?– Is screen compatible with vacuum?
• Open questions:– Good field region within dipole.– Optimum camera distance from beamline to
minimise damage but maximise light.– Electron/photon transition from vacuum to
atmosphere (light tight).– Fresnel lens/Herschelian Telescope optics.– “Modifications” to CNGS tunnel…
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