KLF beamline meeting - September 19, 2024

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Agenda

  • Announcements
  • Detector rates simulations in GEANT4 (Richard)
  • Engineering design progress (Tim)
  • Any other business

Minutes

Present: Vitaly, Richard, Hovanes, Moskov, Pavel, Beni, Tim, Josh, Edy, Eugene, Mikhail, Igor, Sashi, Sean, Chris, Richard, Igal, Lubomir, Justin.



  • Eugene announced that JLAB management is severely limiting procurements until end of October due to budget constraints, including capital construction projects like K-Long.



  • Pavel looked at the beam size and the spectra of the particle incident on the cryo-target using his FLUKA model.
  • Vitaly asked if the rate of the low energy photons not shown on the picture is still high. Pavel's estimate for the photon rate on the target is still around 1.6GHz.
  • Igor and Moskov did not think it was worth looking at muons rates since they will not impact data and physics analysis. Igor also commented that Pavel should work on CPS design and not on the collimator cave. Eugene view was that we are evaluating all of the aspects of the beam after and KPT, and the rates of all particle types should be evaluated before finalizing the engineering design.
  • The beam size without shielding wall after the PS detector is 12cm in diameter, while with a shielding wall with a 6cm aperture for the beam pipe the beam size at the target is about 6cm in diameter.
  • Pavel suggested installing a collimator right in front of the target cart snug around the beampipe as we need to replace the PS shield wall with something else. The collimator would consist of a ~15cm layer of CuW followed by about 10cm borated polyethylene.
  • Tim said that such a small collimator could be attached to the target cart and can easily be supported by the part of the platform under the target.
  • Mikhail found suspicious that the beam pipe with the flanges would not clean up the neutrons. At this time, Pavel does not have details of the beam pipe, like the flanges, in his simulations.
  • Hovanes pointed out that both Igor's MCNP6 simulations and Pavel's FLUKA simulations suggest on the order of ~30mrem/hr dose rate at the SC SiPMs, mostly from neutrons. Attenuating the neutron rate may help reduce the dose rate at the SiPMs, thus increasing the livetime of these SiPMs.
  • Pavel also thought it might be good, for the radiological point of view, to remove the permanent magnet and PS magnet field. That way, the elliptical pipe inside the permanent magnet will not be a source of secondary particles reaching the target. Instead one could install a collimator in the cave so that there will be a collimated muon beam in the beampipe all the way to the photon beam dump. Mikhail though that this may not be feasible because of the problems with a large number of charged particles reaching the target and detectors. Pavel did not think there were other charged particles in the beamline other than muons, but he agreed that it may be problematic for physics. But he thought it would be worth studying this option.
  • Richard commented that he does not believe that, as far as kaons are concerned, the elliptical pipe in the magnet does not block a significant fraction of them. Richard also sees clumps of muons that are bend by the magnet out of the beamline that would otherwise go into the target and may cause problems in the physics analysis.
  • Hovanes asked about the direction of the field in the permanent magnet in the collmiator cave. Hovanes thought it was bending in the horizontal plane, while Richard's GEANT4 has it bending particles in the vertical plane. Tim will check on how the permanent magnet is installed in the cave.



  • Richard simulated 5B γ-events that correspond to 1.2 msec of KLF nominal beam time. This time the target was empty in his simulations as compared to the full LH2 target in the simulations two weeks ago. He also reduced the density of the tungsten compound material to 16.5 g/cm.
  • In general, Richard's conclusion is that emptying the target does not help with the detector rates. In fact, the rates in SC and CDC went up by 20%-30%, most likely due to the fact that the tungsten blocker material reduction. This indicates that the rates in the detectors have a pretty good sensitivity to the tungsten thickness, which is encouraging.
  • The absolute majority of the SC hits happen at the "nose" section of the start counter.
  • Richard also sees a large spike of the rate in the very upstream section of CDC.
  • The first TOF plane seems to absorb significant amount of the noise as the second TOF plane shows less rate near the beamline.
  • Igor thought that it would be good to not deviate much from the 10cm tungsten thickness. Hovanes and Moskov disagreed as the current design allows for too high detector hit rates and occupancies to be able to run the experiment at all. Hovanes' opinion was that we need to improve the detector rates by at least factor of five, and not by the beam current reduction.
  • Moskov suggested to simulate different tungsten thickness to see if the detector rates can be made acceptable. These seems to be the most important next step. The values of the thickness increments for the next GEANT4 simulations would be +1cm, +2cm, +3cm.
  • Moskov also suggested trying to simulate a barrel-shaped start counter of the same length as the current SC (no bent nose section) at some point.
  • Hovanes suggested to restore the K-Long statistics at the source so that we could also see what GEANT4 predicts for kaon flux attenuation for each thickness of tungsten blocker.
  • Beni thought that we might need more than factor 10 improvement in the rates of the photons or whatever is causing these high rates as the CDC and FDC voltage trips start much earlier than the TOF and SC problems start. The occupancy plots for DCs only indicate how problematic the reconstruction will be in terms of efficiency, but they are not a solid indicator of us being able to operate these detectors. Hovanes agreed that the factor of 5 of background rate improvement that he mentioned was optimistic.
  • Justin suggested that we fist need to define criteria for deciding what tungsten thickness would be optimal from these GEANT4 simulations without going through the reconstruction of the events.



  • Tim reported that the engineering group is making progress with the design of the shielding of the CPS. They are working with Pavel to make sure that the radiological environment provided by the CPS design is acceptable for conducting the experiment.
  • Josh said that the CPS magnet vendor will obtain the steel in November and the conductor in October. There are discussions with the vendor to eliminate any confusions regarding the radiation hardness of the hardness of the material that will be used for the coil insulation.
  • KPT engineering design is on hold waiting for the decisions on the tungsten blocker, photon beam requirements.
  • Tim would like to get the preliminary layout of the KFM detector components and the insertion device from Mikhail so that they can start working on the engineering design and drawings for KFM installations.
  • Power supply for CPS magnet is expected to arrive in February or March. The plan is to test the CPS magnet in the spring and the summer. There is also a preliminary plan for testing degaussing with the new power supply of a dipole provided by the magnet group.



  • Moskov asked Hovanes to include Sasha into the beamline mailing list.



  • Next meeting will be held on September 26th.


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