Present: Patric Muggli, Arthur Clairembaud, Michele Bergamanschi, Vittorio Bencini, Marlene Turner

Decision:

• Considerations/general discussion leading to the decision above:

  • Eleven plungers have been ordered (one spare)
  • Option of having two laser beam dumps in one plunger needs to be confirmed by WDL (meeting 15/03/2024 at 1pm)
  • Screens do not wear
  • Double screens do not make sense as the screen would have to be mounted at a different angle to fit into the holder and would not increase the field of view transversly
  • For slot 2 of location 5.5m, we will prepare a beamdump and order a screen in case new information comes up
  • First 5 beamdumps mainly relevant for growth studies (few dedicated measurements), last 5 for confirming stability of wakefield amplitude (may require searching)
  • Laser beam dumps will have a limited number of shots per slot (between 1000-2500)
  • On any given day a plunger will have three positions 1) out, 2) in beam dump, 3) in screen
  • Positions can be shimmed by spacers, but require tunnel access
  • Wakefield stability will be shown on the last 3-4m --> therefore these should have double screens
  • A screen at 9.5m would allow to confirm trajectories and optics
  • However, there is an alternative: mini-quad scans on one screen and trajectory prediction (extrapolation) from the first 5-6 screens
  • Plungers will go over the pipe center (e beam will be approaching from the right in direction of beam travel) naturally as laser beam dump will be on the more aisle side slot. 
  • To do: check the field of view of camera and ensure a minimum depth of field on the order of 1 cm
  • for e-beam commissioning: should take the time to redo orthogonal steering calibration using two screens in plasma as this will greatly speed up alignment (time estimate 1-2 days)
  • if there was a need to injection > 5.5m (unfavourable because of large uncertainties), we can use upstream screens for steering
  • first few screens required to measure proton defocusing as a function of plasma length to confirm where particles are defocused
  • will need to have clear program and start with very few measurement with large differences, since only single beam dumps at these locations
  • screens must never be used as beam dumps (on purpose or accidentally)
  • screens may be able to measure protons and electrons at the same time (depending on light yield)
  • if screen position reproducibility is not sufficient, we may be able to detect edges or markings or always measure protons together with electrons
  • idea Nikita: may remove screens and use plasma light after that to confirm trajectory is still ok
  • need to think about camera settings (filter, aperture) and see how they can serve best all functions
  • e-beam trajectory:
  • maximum of 5mm offset, more typically <2 mm on a screen 1m upstream with beam sizes < 1mm--> To do: define initial screen positions for WDL, shimming requirements
  • optics optimizer uses 200um spot size at target, however then returns the converged result, optics not expected to change much if one would optimize to 0 um spot size
  • contribution of dispersion is small
  • maximum beamsize at the plasma entrance is ~2mm for current optics
  • screens need to be ordered asap (today)
  • design has been optimized by WDL for field of view
  • round and rectangular screens have 4 weeks less lead time (8 weeks instead of 12 weeks)
  • when beam dump foils break through, we may see it on the plasma light cameras
  • for safety, all diagnostics before lpdp3 will always be out
  • future meeting on effect of scattering of e-beam in foils will only be informative, but not change the design above
  • mean scattering angle is theta = 13.6 / E sqrt(d/xo), where d is the foil thickness and xo the radiation length (9cm for Aluminum)
  • we should provide a short summary of all possible measurements to WDL so that they can confirm that these are indeed possible for this design