Feb 21 2024

From last time

• Beam simulations
• ME
  • Gabriel provided Keith Harding with 3D model of the new Pierce cathode front end with 16 deg cone and 30 deg junction angle
  • They have now a 3D model of the front end piece with the corresponding specs before polishing. This drawing is going to be sent to the machine shop for fabricating two samples. One sample will polished. Then th un-polished and polished samples will be measured (hole diameter) to estimate how much the size increases after polishing. After that the model will be updated and sent back to Gabriel for cross-checking. The expectation is that the dimensions, (particularly hole diameter) after polishing should match the ones of the 3D model used for simulations.
  • Machine shop expect to have the two samples ready by end of February.
• Technical Note
  • Gabriel to start drafting a procedure for developing electric fields maps in CST starting from ME models and implementing them in GPT
  • Max to coordinate the procedure writing with Gabriel and with Alicia to capture steps for model validation with beam-based measurements, and with full injector GPT model

Discussion

• Max's simulation results:
  • With optimized solenoid settings for R28 and different R30 cases, all reasonable gun models can be made to behave about the same. The 140 kV settings found this way are only 10% off from what was in the machine during setup with Wiens off.
  • Beam size in solenoids: useful lower limit determined by initial emittance and distances; upper limit determined by onset of emittance increase due to aberrations, RMS about 2 mm for CW (!) and 3 mm for SW
    • This means the shorter the focal length (-> less astigmatism + big beam), the better the SW configuration. SW is worse only when Larmor rotation (irrelevant for round beam) causes more effective emittance increase than aberrations. Need to investigate this for a realistic range of beam parameters from the gun.
• Alicia's simulation results
  • Discuss the objectives of the next simulation

Path forward, conclusions

• 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.

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