AWAKE Electron Spectrometer

1. AWAKE Electron Spectrometer Simon Jolly 7th March 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 Collaboration Meeting

3. Spectrometer Layout (Isometric View) CERN 1 m dipole Scintillator Screen Protons Electrons + Protons Camera Plasma cell • Edge of scintillator screen is aligned with dipole coils (position will depend on resolution). • Screen mounted at 45 degrees to beam axis. • Camera is 4 m from centre of screen, mounted at 90 degrees to beam axis. • Camera shown in horizontal bending plane. • Camera can also be mounted vertically, directly above screen, with screen tilted at 45 degrees to vertical as well as 45 degrees to beam axis. Dipole to screen distance remains unchanged (independent of screen-camera orientation). Simon Jolly, UCL, AWAKE Collaboration Meeting

4. Spectrometer Layout (Plan View) Electrons + Protons • For left-hand bend, beam enters at right-hand edge of dipole. • Protons essentially unaffected; electrons bent in dipole field. • Screen mounted at 45 degrees to beam axis. • Camera is 4 m from centre of screen, mounted at 90 degrees to beam axis. CERN 1 m MBPS dipole 1.6 m Electrons 1 m Protons Camera Scintillator Screen 4 m Simon Jolly, UCL, AWAKE Collaboration Meeting

5. Spectrometer: Vacuum Vessel Electrons + Protons • Screen mounted inside vacuum vessel, but camera outside. • Light tight path from vacuum window to camera: doesn’t need to be permanent, just light tight… Vacuum Vessel Camera Vacuum Window Light Tight Path Simon Jolly, UCL, AWAKE Collaboration Meeting

6. Spectrometer: Shielding Electrons + Protons • Most important item to shield is CCD Camera. • Needs to be as far from beamline as possible (while still close enough to receive enough light). • Maximise distance to beam axis. • More shielding required on upstream side. Vacuum Vessel Shielding Simon Jolly, UCL, AWAKE Collaboration Meeting

7. CERN 1 m Dipole (Edda, Alexey) Simon Jolly, UCL, AWAKE Collaboration Meeting

8. Spectrometer Simulations • Initial simulations of Spectrometer layout carried out by Alexey: • Effects of upstream quadrupole doublet. • Quick check of fringe field effects. • More detailed simulations by Dan Hall (UCL) including Spectrometer GUI for checking spectrometer layout parameters quickly. • GPT simulations using beam parameters from K. Lotov (good and bad…) for design setup, with and without fringe fields. Simon Jolly, UCL, AWAKE Collaboration Meeting

9. Spectrometer GUI: Assumptions GUI and movies courtesy of Dan Hall (but don’t tell him…). Simon Jolly, UCL, AWAKE Collaboration Meeting

10. Electron Beam Distributions Good (“2 GeV”) Bad (“650 MeV”) Simon Jolly, UCL, AWAKE Collaboration Meeting

11. 2 GeV, 1.86T: Trajectories Simon Jolly, UCL, AWAKE Collaboration Meeting

12. 2 GeV, 1.86T: Screen Simon Jolly, UCL, AWAKE Collaboration Meeting

13. 2 GeV, 1.86T: Screen (Zoom) Simon Jolly, UCL, AWAKE Collaboration Meeting

14. 2 GeV, 1.86T: Spectrometer Energies Simon Jolly, UCL, AWAKE Collaboration Meeting

15. 2 GeV, 1.86T: Energy Correlation Simon Jolly, UCL, AWAKE Collaboration Meeting

16. 2 GeV, 1.86T: Energy Correlation (2) Simon Jolly, UCL, AWAKE Collaboration Meeting

17. 2 GeV, 1.86T: Energy Resolution Simon Jolly, UCL, AWAKE Collaboration Meeting

18. 650 MeV, 1T: Screen Simon Jolly, UCL, AWAKE Collaboration Meeting

19. 650 MeV, 1.4T: Screen Simon Jolly, UCL, AWAKE Collaboration Meeting

20. 650 MeV, 1.86T: Screen Simon Jolly, UCL, AWAKE Collaboration Meeting

21. 650 MeV, 1T: Spectrometer Energies Simon Jolly, UCL, AWAKE Collaboration Meeting

22. 650 MeV, 1.4T: Spectrometer Energies Simon Jolly, UCL, AWAKE Collaboration Meeting

23. 650 MeV, 1.86T: Spectrometer Energies Simon Jolly, UCL, AWAKE Collaboration Meeting

24. 650 MeV, 1.86T: With Fringe Fields Simon Jolly, UCL, AWAKE Collaboration Meeting

25. 2 GeV, 1.86T: With Fringe Fields Simon Jolly, UCL, AWAKE Collaboration Meeting

26. 2 GeV, 1.86T: Spectrometer Energies Simon Jolly, UCL, AWAKE Collaboration Meeting

27. Conclusions • Fundamental design hasn’t changed: it’s still simple! • Already have camera (but not lens) and magnet (but not power supply). • Some nice simulation results from Dan Hall using Konstantin Lotov’s beams: • Preliminary results show we can resolve the energy distribution reasonably well. • With Konstantin’s parameters, energy spectrum not washed out by emittance. • Fringe fields start to affect large angle beams at low energy + high fields, but otherwise okay. • A note of caution: • These are “idealised” fringe fields. • May have nonlinearities/nonuniformities in actual magnet field. • Definitely need magnetic field mapping + magnet “ramp” (hysteresis + power supply). • Onwards to finding a scintillator… Simon Jolly, UCL, AWAKE Collaboration Meeting

28. CDR/Technical Note Status • Matt Wing looking after spectrometer text/figures for CDR: • Text written. • Will include 1 or 2 plots I’ve just shown you. • Technical note is somewhere between “draft” and “almost” done: • Have received corrections from Matt Wing and Patric Muggli on Design + Layout sections. • Simulations/Energy Reconstruction mostly plots: you’ve just seen them all… Simon Jolly, UCL, AWAKE Collaboration Meeting