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AWAKE Electron Spectrometer

Detailed specifications and status updates on the AWAKE Electron Spectrometer project presented by Simon Jolly at a UCL meeting on November 6, 2013. The layout, components, and considerations such as scintillator selection and simulation using GEANT4. The critical role of the scintillator in determining the spectrometer's performance is highlighted along with the need to optimize light output levels. Challenges, progress, and conclusions from the project are discussed.

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AWAKE Electron Spectrometer

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  1. AWAKE Electron Spectrometer Simon Jolly 6th November 2013

  2. 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. Simon Jolly, UCL, AWAKE-UK Meeting

  3. Spectrometer Status • Energy reconstruction with Lotov’s beam distribution show good match (Dan Hall). • Confirmed with CERN that CAD models of experimental area can be shared and modified: • Ans Pardons CERN contact. • CERN uses CATIA, we have Autodesk Inventor: reasonably consistent import/export using native file formats. • Gone rather quiet… • Some discussions with Patric Muggli over vacuum vessel: • Light tight path needs some thought so as not to interfere with beamline maintenance. • Largely dependent on spectrometer layout: camera position. • Scintillator light output: • Scintillator performance crucial for this design. • After hiatus, giving it both barrels: • Lawrence Deacon (postdoc). • James Goodhand (MSci). • GEANT4/BDSIM simulations: start with better-known scintillators… Simon Jolly, UCL, AWAKE-UK Meeting

  4. 2 GeV Beam, 1.86 T Field Simon Jolly, UCL, AWAKE-UK Meeting

  5. 2 GeV Beam, 1.86 T Field Simon Jolly, UCL, AWAKE-UK Meeting

  6. 2 GeV Beam, 1.86 T Field Simon Jolly, UCL, AWAKE-UK Meeting

  7. 2 GeV Beam, 1.86 T Field Simon Jolly, UCL, AWAKE-UK Meeting

  8. 2 GeV Beam, 1.86 T Field Simon Jolly, UCL, AWAKE-UK Meeting

  9. 2 GeV Beam, 1.86 T Field Simon Jolly, UCL, AWAKE-UK Meeting

  10. AWAKE Experimental Layout

  11. Spectrometer Layout Scintillator Screen Protons CERN MBPS dipole Electrons + Protons Camera Plasma cell

  12. Spectrometer: Vacuum Vessel Beampipe Electrons + Protons Vacuum Window Camera Vacuum Vessel Light Tight Path Simon Jolly, UCL, AWAKE-UK Meeting

  13. 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. • Radiation hardness. • Area. • We don’t care about: • Speed. Simon Jolly, UCL, AWAKE-UK Meeting Vac. Chamb. (grey)

  14. GEANT4 Simulations (Lawrence) • Have set up simulation using GEANT4/BDSIM • Beginning to use it to test required vacuum level (initially air at STP vs vacuum). • Included scintillation and reflection/refraction processes in screen – currently crystal YAG:Ce quadrupole Coils (yellow) Vacuum Chamber (grey) Yoke (green) Camera plane Scint. screen Poles (blue) Simon Jolly, UCL, AWAKE-UK Meeting Vac. Chamb. (grey)

  15. GEANT4 Simulation Status • Plan to include necessary optical processes in screen – scattering, absorption etc. to obtain realistic optical photon distribution • e.g. for Lanex screen: • Particle size ~ photon wavelength -> Mie Scattering. • Optical surfaces – reflective back surface etc. quadrupole Coils (yellow) Vacuum Chamber (grey) Yoke (green) Camera plane Scint. screen Poles (blue) Simon Jolly, UCL, AWAKE-UK Meeting Vac. Chamb. (grey)

  16. Conclusions • Scintillator selection key to spectrometer performance. • Light output levels from scintillator sets almost entire spectrometer geometry. • Set camera position/distance from solid angle scintillation photon distribution. • Check “standard candle” scintillators – YAG:Ce etc. – in GEANT4 before moving on to granular Lanex. • Need to pin down Lanex properties: previous GEANT4 simulations are scarce… Simon Jolly, UCL, AWAKE-UK Meeting

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