5/18/23 -- Making beam at LERF -- Max, Steve Benson, Joe Gubeli

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We are investigating how the LERF would do as a test environment for the target.

  • The LERF can easily make the beam parameters we need.
  • Options for location of setup and beam energy:
    • Baseline 7 MeV: In principle, there is a free port that would let us go straight through the merger dipole and attach our setup there. But, while there is nothing installed in that area, the space is needed to move cryomodules in and out of the cave for testing. While conceptually very simple, this is not a good option.
    • A very convenient location for the experiment would be at the end of the line where the isotope experiment used to live. One cannot easily float 7 MeV through the cryomodule with all cavities off, but it is known that one can get 10 or 12 MeV to the end of that line by accelerating and decelerating. It seems reasonable to assume 7 MeV would work, too, given some tweaking.
    • This could stay the baseline, but we would also have the option of running beam to the target at up to 30 MeV "for free" if we wanted to; I don't know if there's any benefit from a target-test point of view, but the option is there. Of course, with the downside of nasty activation.
    • There is already a nice dump with adequate shielding there.
    • The shielding configuration would need to be modified if the target was very tall (need to look at the numbers). We might be able to reuse a lot of existing items if we plan well.
  • Beam parameters and diagnostics:
    • Spot sizes are measured with YAG viewers by running at full bunch charge and low duty cycle. There are no harps, but we could consider adding one if we wanted it. There are no viewers inside the dump enclosure because of radiation concerns; if we wanted one, we would need some optics to bring the light out to an external camera.
    • The bunch frequency is very small compared to CEBAF and UITF default modes, only a few megahertz. The machine is designed for > 100 pC bunch charge, and the high gun voltage and compact injector make space charge less of a concern. We will need to evaluate if this affects us. There does not seem to be a fundamental reason why the frequency would need to be low for what we are trying to do, but there isn't necessarily a reason to change it, either.
    • Chris Tennant has a complete Elegant model that was used for the isotope experiment.
  • Operational aspects:
    • The project would not need to cover the full running cost of the machine, but it would need a LERF operator to fulfill staffing requirements.
    • We don't know what state the machine is in; things may be broken. Steve would like to run the klystrons and see if they still work. The rest of HCO would take place as part of the project.
    • There are two helium leaks. One is in the booster and likely of the kind that only appears below the suprafluid transition. It will limit the cathode lifetime but not prevent us from running. The other leak is somewhere in the full cryomodule and causes a downstream vacuum pressure of 1e-8 mbar even with a turbo running. While the pressure itself is not a huge issue from the experiment's point of view, what it mostly does is prevent the cavities from reaching high fields because the helium will get ionized and mess with the resonance. This may not be relevant at the fields we need to get the beam through.