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Electron Spectrometer Meeting

Present: Matthew Wing, David Cooke, Fern Pannel, Arthur Clairembaud, Edda Gschwendtner, John Farmer, Marlene Turner, Debdeep Ghosal, Joe Wolfenden, Patric Muggli (first half)

Discussion points:

• Run 2c spectrometer chamber: an angle of ~14 degrees works for all.
  → Action: MT to communicate to Nicolas.

• OSR port will not need a special angle.
  → Action: DG and JW to have a careful look and do calculations based on example parameters.
  → The forward cone of OSR is small; a DN 40 port was sufficient at CLEAR for a 150 MeV beam.
  → DN 40 port should also work for AWAKE; check with Nicolas if DN 63 would also be possible.
  → Action: DG and JW to think about an alignment procedure for OSR.
  → Idea: possibly use a periscope to transport light downwards.
  → Action: JW to investigate if a Basler camera can also be used for the diagnostic.

Emittance measurements with spectrometer screen:

• MT: How will the plasma exit ramp affect the emittance and the measurement?
  JF: First simulations with the entire proton bunch show a huge detrimental effect (emittance increase of the witness in the exit ramp).
  → Action: JF to present simulation results at the next meeting.

• Is it a problem that the waist location is no longer at the plasma exit?

• Problem is not the emittance measurement itself (the diagnostic will measure the emittance), but that simulations suggest the current configuration is not usable to fulfill the Run 2c goal.
  Comment MT: We need to re-evaluate the situation and only then decide on emittance diagnostics.

• Comment JF: A discharge source with an exit window would avoid the exit ramp problem.
  General comment (not mentioned in the meeting): the discharge source has not yet reached the required density uniformity for acceleration.
  
  

Emittance analysis
→ Action: DC to present analysis of the 4e14 dataset at the next meeting.
→ FP: We may have additional data, e.g. also at 7e14 (since every time we did a measurement with plungers, we also put LBDP2 in).
→ Action: FP and DC to coordinate and look at the data.

New VB2 dipole magnet

• No one sees any showstoppers to moving over to this magnet.

• Only left to do:
  → Action: MT to get approval from Gilles Le Godec.

• Even with the higher dipole aperture, there is no need for the scintillation screen to be wider.

• → Action: MT to check if this magnet is indeed a C-shaped magnet (based on a comment by MW).

• The magnets team has shared the B–I curve, but it only reaches up to 400 A.
  DC: Baseline is to use this magnet at 500 A. The field at this current is therefore unknown.
  → Action: DC to share what B-field is needed to measure the emittance of a 10 GeV beam.
  
  

More space downstream of the plasma needed

• MT noted it would be advantageous to have more space between the plasma exit and the first quadrupole magnet, since many instruments will need to be added there: bellows, beam dumps, beam instrumentation, expansion volume, etc.
  → Action: DC to investigate if this distance can be increased (to ideally 4 m) without sacrificing the possibility to measure a 1–2 mm mrad 10 GeV emittance beam.
  
  

Specification document
→ Action: DC to update (focusing on the parts that will likely not change) and use the correct template.

Next meeting: 17th of September
Agenda: Update on the emittance analysis from Run 2b; simulations of the plasma exit ramp.