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AWAKE Run 2bc Spectrometer
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CERN
CERN
AWAKE Run 2bc Spectrometer
Electron Spectrometer Meeting
Present: Matthew Wing, Fern Pannel, Arthur Clairembaud, Edda Gschwendtner, John Farmer, Marlene Turner, Joe Wolfenden, Patric Muggli, Collette Pakuza
Action follow up:
Marlene noted that we may need to choose between two options 1) Using the dipole magnet with the smaller opening aperture (8 cm) at the specified B-field (integrated 3.5 Tm), while accepting background from the proton beam halo interacting with the chamber and the magnet, or
2) Switching to the 10 cm opening aperture magnet (VB2), and accepting a lower integrated B-field. An email from Gilles suggests that he would approve using the magnet at 360 A, corresponding to a field of: ~2.2 Tm. Action UCL: check if 2.2 Tm would also be ok. Marlene already asked if he would also be ok if we used the magnet at 540 A, no response yet.
Presentation on Plasma Exit Ramp Simulation Results (John)
- Due to the proton bunch density modulation after self-modulation, no significant electron filament is observed in the exit ramp.
- The geometric emittance—or the normalized emittance (geometric emittance × average gamma of the beam)—does not grow significantly in the plasma exit ramp for this electron beam energy.
- It still needs to be checked what happens if there is an offset between the electron and proton beams at the plasma exit.
Follow-up actions:
- David and the UCL team: Use the output beam distribution from the plasma simulations as input, propagate to the spectrometer, and measure emittance to check how accurately the measurement reproduces the actual beam emittance.
- Joe and Debdeep: Use the output beam distribution from the plasma simulations to calculate OSR emission and emittance, and check how accurately the measurement reproduces the actual emittance.
Emittance Analysis – Measurements (Matthew for David)
- At 400 MeV accelerated electron beam energy, an emittance increase is observed due to beam scattering in the laser beam dump.
- At 850 MeV and 1500 MeV, no measurable emittance increase is observed.
- Calculated increase of the geometric emittance (using GEANT4 simulations) is from 3 to 7 mm mrad for 400 MeV, 2 to 2.2 mm mrad for 850 MeV and 0.6 to 0.65 for 1500 MeV in a 300 um thick Aluminum foil.
Remaining open actions:
- Action: DG and JW to review carefully the spectrometer dipole chamber design and perform calculations based on example parameters.
- Action: DG and JW to consider an alignment procedure for OSR.
- Action: JW to investigate whether a Basler camera can also be used for the diagnostic.
- New VB2 dipole magnet: Action: MT to obtain final approval from Gilles Le Godec that the VB2 can be used.
- Action: DC to share what B-field is required to measure the emittance of a 10 GeV beam.
- Action: DC to investigate whether the distance can be increased (ideally to 4 m) without losing the ability to measure a 1–2 mm·mrad, 10 GeV emittance beam.
- Action: DC to update the specification document (focusing on parts unlikely to change) and ensure the correct template is used.
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