Jan 30 2024

Actually, Jan 31.

Action items from last time

• Carlos will develop a high-level timeline for the rest of the project.
• Now that the simulation models are working well, Max and Gabriel will optimize
  • the Pierce angle to give R28-like optics as a baseline and
  • the junction angle to allow for a larger lip radius, and less field enhancement. Carlos does not insist on the steep angle of R30-3, it can be a smooth transition.
• We will make two electrodes to have a spare; one can consider making two different shapes as a contingency plan. Carlos will ask Keith to join the meetings.
• Max will consolidate the set of field maps for apples/apples comparison in Alicia's injector model. Alicia will make a comparison between the updated R28, R30-3, and R30-4 models and work toward defining an acceptance band for phase-space parameters at the match point.
  

Updates and discussion

• Link to schedule SharepointLink to schedule in Sharepoint
• Keith Harding reports it will take him ~ 3 days to modify the existing R30-3 Pierce front-end piece and make TWO new models per Max's design. Carlos told Keith the following parameters will change from the original R30-3 drawing:
  
  • Hole diameter
  • Pierce angle
  • Junction angle
  • Lip radius
• Carlos sent the barrel polishing technote to Jessica and Chris Dreyfuss (he is in charge of the SRF tumbler polisher). The three met and discussed a plan to practice polishing a test piece to be ready when the actual pieces come from the machine shop.
• Max and Gabriel: CST model gives believable results, no remaining mysteries between CST and Poisson. Simulation results for different parameters...
  • Beam envelopes for 15,16,17,18 degrees Pierce angle
  • Focal length vs spot position
• Some more data from large-active-area R28 test at 200 kV:
  • Applied beam-based BPM linearity correction
  • Zero-corrected BPM signals to symmetry axes of gun kick
  • Interpolated beam angles
  • Beam angles UITF vs. GPT
  • Extrapolated rays including solenoid data
  • Angle from solenoid measurement sensitive to small model errors, but beam position in reasonable agreement
  • Measured aberration in qualitative agreement with model, albeit focal length shorter overall. Focal length was longer in previous runs, so possibly due to different cathode recess with this puck. Can probably adjust the model to make data agree.
• Alicia has performed GPT simulations with the updated R28 and R30-4 candidate field maps.

Conclusions, path forward

• No showstoppers identified, reasonable confidence in models established.
• Time line does not leave enough room for a bake+HV test on the bench but has plenty of safety margin otherwise.
  • Carlos will incorporate into the time line a potential vent and electrode swap in case of failure to HV-condition or get the beam out (by no means anticipated, but good to know how long it would take)
• By next meeting, Max, Gabriel, and Alicia will complete simulations of:
  • shallow junction angle
  • tolerance bands around nominal values, especially cathode recess, to evaluate injector acceptance (see parameter table from last meeting).
  • Final checks: tilted anode, biased anode, 140 kV
• Deadline to define Pierce angle: Wednesday, February 7, 2024. Max, Alicia.
• Deadline to provide Keith Harding with the chosen models (TWO Pierce angle options): Friday, February 9, 2024. Max, Gabriel.
• February 13, 2024. Present before the B-Team meeting the strategy followed for arriving at the optimized Pierce angle. Max and Alicia.
• Geometrical parameters downselect

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