Feb 28 2024

From last time

• Simulations
  • Max:
    • Repeat simulations from today's presentation but with space charge ON and with Moller specs bunch charge / beam current.
    • Add dipole field map to simulations.
    • Add to simulations graphics location of first beam viewer screen
    • Continue exploring option B, perhaps with slightly stronger focusing compared to option A(16 deg / 30 deg) Pierce angle cathode front end, but do this with space charge ON and with Moller spec bunch charge
  • Alicia: Add emittance to slides from today's presentation
  • Yan: Develop beam studies plan (ATLis) to implement BEFORE SAD for measuring beam size at Y-chamber viewer vs first solenoid BDL (or current) for R28 gun operating at 140 kV. Results will then be compared with beam envelope simulation results from Max and from Alicia.

• ME
  • Carlos:
    • Add to schedule fabrication of "plan B' second choice Pierce angle cathode front end.
    • Check actual design and manufacturing progress of plan A (16 deg / 30 deg) Pierce angle cathode front end against schedule.
    • Define milestones and deadlines
• Documentation
  • Gabriel: start writing a technical note detailing the process and steps from concept anode-cathode geometry to production of electric field maps and implementation to GPT. Consideration such as puck position wrt to plan of the electrode hole must be described, as well as process for parametric geometry studies including Pierce angle, hole size, junction angle between spherical electrode and front end cathode. Include process for validating CST against POISSON, etc.

Updates

• Max:
  • 15° dipole simulated and compared with measurement
    • discrepancy in horizontal (de)focusing yet to be understood
    • measured skew coupling likely caused by VIP1I01, planning to mitigate it... could be included in GPT if needed
    • these effects are small compared to the possible variations in gun optics; our not fully understanding them yet is not prohibitive to gun redesign
  • optimized lens settings with space charge: 200 kV, solenoids SW vs. repaired CW
    • all four setups are optimized independently for minimum beam sizes in MDR1I02 and MWF1I04
    • beam size/divergence depends on space charge, but optimum BDL for solenoids is only weakly dependent
    • SW solenoids cause emittance exchange due to gun astigmatism, but this gets removed by the second one, no significant difference downstream compared with CW
  • design strategy for Plan B electrode driven by possible failure modes: a) beam optics, b) FE / HV breakdown, c) something we are overlooking entirely
    • a) not much freedom to further reduce the Pierce angle without moving the cathode in z, so we're not changing it; no obvious reason to want to increase the focusing strength from nominal
    • b) the only degree of freedom is the junction angle; try to maximize it without exceeding surface-field threshold on lip. Gabriel to provide final numbers
    • c) no idea what to do about this, so fingers crossed
  • Gabriel
    • CST simulations looking at the gradient of the lip and junction for various junction angle options.
      • R30-4 junction angle and lip radius gradients vs junction angle

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