awake electron spectrometer

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

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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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