Shielding optimization meeting (2/10/23)

SUMMARY NOTES

PARTICIPANTS: Pavel Degtiarenko, Bob Michaels, Bogdan Wojtsekhowski, Gabriel Niculescu, Tanja Horn, Steven Lassiter, Bert Metzger, Rolf Ent, Dean Spiers

SIMULATIONS FOR SHIELDING OPTIMIZATION

• Background: need to still purchase borated poly and either lead or tungsten

• Simulations performed to determine the lead/tungsten needs

Model update and simulation results (Pavel D)

• Framework: FLUKA

• Model uses Gabriel's model and assumes that only the quantities of lead and tungsten currently available can be used

• Action item: consider relaxing that requirement and allow to include more lead and/or tungsten to optimize shielding

• Items investigated

• 1) power deposits
• 2) Exit beam line

• Power deposits based on this model (total power delivered to all regions 11 GeV, 2.7 uA beam

• Absorber 30 kW
• Forward Cu-W plate 1 kW
• Exit beam line 0.1 kW
• W powder blocks 0.07 kW
• Poles 1 kW

• With this model can conclude:

• tungsten copper model on top and bottom not much power deposit
• most power deposit in the forward region (region 3 on Pavel's slide)
• Action item: consider extending the dimensions of the copper and use mechanical connection forward Cu-W plate to absorber itself

• Mechanically can still make such changes to the absorber and Cu-W

• what needst to be designed is the cooling for region 3
• need air spaces

• Shape of the Exit Beam Line

• need to increase 3x3mm channel to 6x6mm in a 4cm Cu-W beam to make sure the beam goes through - it's not strictly speaking a "collimator"

• Photon beam quality: >99% photon beam

• Beam power distribution of photons and lepton pairs - measured in dose rates

• overall very clean
• photon profile has a "shoulder" due to the absorber - background exiting CPS - have about 10% low energy background that has a higher probability for scattering
• wings that one can see in prompt photon radiation are also due to low energy background scattering

• Note: here use a W shielding configuration that is mostly symmetric using W as it has been bought so far

• optimizations are made by making profiles equal

• Prompt radiation dose rates

• on top of the Hall dome outside are typically 1-3mrem/h for high power experiments in Hall C
• here, the estimates show levels under 2mrem/h at 11 GeV
• Lower energies are expected to generate lower dose rates

• Radiation dose rates from activation 1 hour after beam off

• overall reasonable - traces of 10-100 mrem/h - this is typical for high power experiments
• remark on oval shape needing redesign

• Radiation dose rates from activation 5 years after beam off

• still very active and needs to be treated carefully
• goal is to never disassemble the CPS
• still see some activation at the flanges beam
• Action item: need to design beam exit carefully to minimize activation of the flanges

• Radiation dose rate at the JLab boundary - about 100m distance from Hall C

• about 10 muRad/h, which is a little higher than seen before. However, need to evaluate now carefully the actual running (energies, time at each energy, etc.)
• higher energy neutrson are most relevant for dose rate outside - and their production depends on energy
• Action item: need schedule of the experiment
• Action item: consider adding more lead on the top - this would help with the neutron prompt radiation dose rates around the CPS

• Note: does this radiation come from the target of the CPS? - from the calculations it looks like more target shielding is needed

• Conclusion so far: it looks like lead can do the job --> have enough tungsten

• can tune boundary radiation by tuning the amount and locations of lead

• Action item:

• check if more tungsten is needed
• if more tungsten needed, then specify how much more tungsten would be needed for any improvement.
• otherwise just add more lead and specify how much is needed

• Total weight of the system: used to be about 53 US tons (from Josh 18 December 2020 presentation: 2391 lead bricks, 2109 tungsten bricks)

• note: weight support in Hall not a problem
• need a crane to move the CPS as a whole though - it will not be disassembled

• To complete model need to add magnetic field for target

• this is expected to improve things

• Next meeting: global CPS meeting on tentatively 3 March