View source for 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