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    Working Group Meeting

    → Europe/Zurich
    Working Group Meeting
    Zoom Meeting ID
    61413407892
    Host
    Filippo Resnati
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    Dante discussed the various processes involved in the scintillation of LAr doped with N2 and Xenon, and the propagation of light.

    N2 and Xe competes to the de-excitation of argon dimers. The scintillation production is not affected by any relevant concentration os Xe and N2 for the singlet component, as it is very fase, but it does affect the triplet component (slower).

    Xenon seems to introduce a cutoff in the transmission of argon scintillation at around 130 nm (what is shorter wavelengths is cut), reason why the singlet component amplitude is affected even by the slightest xenon concentration.

    N2 and Xe mask each-other's effect on the LAr scintillation, reason why is difficult to measure small N2 concentrations in Xenon-doped LAr.

    Dante proposes tests at PuLAr of scintillation response of Xe doped (10 ppm) and N2 doped  (different values) LAr. This measurement will inform if the expectation from the model are correct and what to expect in the similar measurement done at NP02.

    To see the reduction of N2 there are two ways:

    • dope NP02 LAr with order of 5 ppm N2
    • find a gas analyser sensitive to 0.1 ppm of N2

     

    It is impractical and expensive to dilute the argon to reduce the xenon concentration, this is not estimated a viable option. Pascoal proposed to study the possibility of developing a filter capable pf trapping xenon.

     

    Pascal showed the procedure to access the mol-sieve filter in NP02, ensuring that the contamination of the Cu filter are minimised, by pressurising the Cu filters with argon gas, and to flowing it out the mol-sieve aperture.

    Risks of exposing the Cu filters to air are very small, and the situation can be monitored with the temperature sensors embedded in the filters.

    Residual risks related to O2 deficiency because having to work with argon flowing can be mitigated.

    The duration of the intervention is estimated to be about 12 days, with very pessimistic scenario extending to 3 weeks. To avoid LAr purity to drop, the condensation must be stopped and the boil-off released to air. This imply a loss of argon of the order of 2.5 tons/day, about 30-40 tons of top up.

     

    Roza discussed a detailed procedure of passivation of the Cu filters. The procedure is based on flowing through the filters using the regeneration piping O2-Ar mixture (though it is said that N2 can also be used instead of Ar), with increasing O2 levels from 0% to 20% vol, while monitoring the temperature of the filters.

    After the Li-FAU exchange/addition, filter regeneration would follow the usual procedure: Ar-H2 mixture for Cu and warm Ar gas for mol sieve (Li-FAU).

     

    To do:

    Filippo, Pascal, Johan and Roza: In case the passivation is needed, figure out how to mix Ar and O2, or understand if pre-mixed cylinders can be used (the limit is the amount of 12 cylinder racks that are needed to fully passivate teh 60 kg of Cu filter).

    All: discus the two scenarios:

    • completely remove the mol sieve and replace it with Li-FAU
    • add Li-FAU to the existing filter (or partially remove the mol sieve to free some space for the Li-FAU while leaving also yeti mol sieve)

     

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