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Working Group Meeting
Pascoal presented his slides, with the measurements already performed in the small test stand at UNICAMP.
He went through the properties of the Li-FAU and how they comprare to the standard 4A mol sieve.
Li-FAU adsorb both water and nitrogen, while 4A primarily captures water.
Because water competes with nitrogen for adsorption sites on Li-FAU, the proposed strategy is to combine the two materials: 4A would remove most of the water, while Li-FAU would focus on nitrogen removal.
Pedro presented a one-dimensional model describing impurity transport and adsorption during LAr recirculation.
The model assumes constant mass flow through the purification column, uniform porosity, and a well-mixed cryostat.
The model includes transport outside and inside the zeolite particles and adsorption on the solid material.
Three parameter can be extracted from the purity evolution.
The model was used to fit data from the PuLArC test stand at UNICAMP and Iceberg at Fermilab.
The model can be used to extrapolate the performance of the filtration medium in NP02.
The model was used to fit the NP02 initial O2 purity, but the assumptions fed into the model were discarded by subsequent experimental observations.
In the model the increase of the impurity during NP02 filling is accounted for by the desorption of O2 from the filter, but regeneration of the filter did not improve the situation, implying that desorption is not the cause of the impurity increase and stabilisation.
The discussion of NP02 purity is taken offline.
Roza explained that significant moisture is expected during initial filling when argon gas will be condensed in DUNE.
During this period a more frequent filter regeneration may be needed.
The current worst-case assumption for LAr purification is approximately one filter regeneration per month, with the actual frequency depending on purity during operation.
The presentation from Dante was moved to next meeting, due to lack of time.
Dante proposed additional measurements to study nitrogen contamination in the presence of xenon and validate the UNICAMP setup.
Measurement with pure LAr, doping LAr with 10 ppm (mass fraction!) of xenon, and then dope with nitrogen in step from 0 ppm to up to 50 ppm.
Next Steps
- Pascoal to share raw PMT waveforms and existing data from UNICAMP.
- Filippo and Dante to investigate availability of TPB coated cryogenic PMT to be used at UNICAMP.
- All participants to review the proposed document structure shared via overleaf and contribute to the text.
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