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35 Ton LAr Impurity Distribution Measurements and CFD simulation

Document #:
Document type:
LBNF/DUNE document
Submitted by:
Erik A Voirin
Updated by:
Stephen Pordes
Document Created:
28 Mar 2016, 15:56
Contents Revised:
29 Mar 2016, 08:27
Metadata Revised:
13 Sep 2016, 16:31
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There are 4 purity monitors in one corner of the 35 TON LAr cryostat which measure electron lifetime, which is inversely proportional to impurity levels. The lifetime measurement at the top and the bottom have always shown a difference in purity levels. In March of 2016, a power outage occurred, which stopped the pumps and purification, and during this time, a homogeneous lifetime profile could be seen, as the top and bottom purity monitors read the same value, and lifetime decreased together. This can be seen in slide 4, where the tag name “35T_PRM_Lifetime_1.F_CV” was the bottom purity monitor, and “35T_PRM_Lifetime_4.F_CV” is the top purity monitor. When the pumps and purification was restarted around 3/7/2016 @ 10:00 am, the vertical gradient in purity levels could be seen again, with higher electron lifetime, and more pure liquid on the bottom of the cryostat. See Slide 5 for data after the pumps were restarted, note there are 4 purity monitors plotted here, #1 through #4 being in order of elevation, #1 near the bottom up to #4 being near the top. Since no gradient was seen with purification off, it was apparent the cryostat did indeed have a real, and large vertical gradient purity.
Since we are conducting Computational Fluid Dynamics (CFD) simulations of the future LBNF cryostat, and making conceptual design decisions based on these simulations, we conducted a similar simulation of the 35 TON cryostat to compare to the measurements and validate the model.
Notes and Changes:
Add topic of Cryogenics WG
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