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AWAKE Electron Spectrometer
Simon Jolly7th March 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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Spectrometer Layout (Isometric View)
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Camera
Scintillator ScreenCERN 1 m dipole
Plasma cell
Protons
Electrons + Protons
• 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).
Spectrometer Layout (Plan View)
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Electrons + Protons
Protons
Electrons
CERN 1 m MBPS dipole
Scintillator Screen
Camera
• 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.
4 m
1.6 m
1 m
Spectrometer: Vacuum Vessel
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Electrons + Protons
Camera
• 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 Window
Vacuum Vessel
Light Tight Path
Spectrometer: Shielding
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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
CERN 1 m Dipole (Edda, Alexey)
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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.
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Spectrometer GUI: Assumptions
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GUI and movies courtesy of Dan Hall (but don’t tell him…).
Good (“2 GeV”) Bad (“650 MeV”)
Electron Beam Distributions
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2 GeV, 1.86T: Trajectories
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2 GeV, 1.86T: Screen
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2 GeV, 1.86T: Screen (Zoom)
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2 GeV, 1.86T: Spectrometer Energies
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2 GeV, 1.86T: Energy Correlation
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2 GeV, 1.86T: Energy Correlation (2)
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2 GeV, 1.86T: Energy Resolution
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650 MeV, 1T: Screen
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650 MeV, 1.4T: Screen
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650 MeV, 1.86T: Screen
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650 MeV, 1T: Spectrometer Energies
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650 MeV, 1.4T: Spectrometer Energies
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650 MeV, 1.86T: Spectrometer Energies
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650 MeV, 1.86T: With Fringe Fields
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2 GeV, 1.86T: With Fringe Fields
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2 GeV, 1.86T: Spectrometer Energies
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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…07/03/13 Simon Jolly, UCL, AWAKE Collaboration
Meeting27
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…
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