AWAKE Electron Spectrometer

Simon Jolly 6th 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.

Aerial & Industrial Markets

©Eastman Kodak Company, 2005

Screen constructionScreen constructionCurl-controlBacking

Polyestersupport

PhosphorLayer

Clearovercoat

178 microns

50 to 305 microns

7.6 microns

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Vac. Chamb. (grey)

GadOx: Geant4 Photons (J. Goodhand)

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And Now: ���A Scintillator Interlude.

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A Scinterlude youtu.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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