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The slow pre-cooling has consistently given higher transfer efficiencies between 56 and 58% but requires long pre-cooling times (~ 4 to 5 hours) with the potential benefit of a slow filling which is still under study. In this mode, the Liquifier LHe level is maintained constant. During the slow pre-cooling, we can estimate when the system is cold enough through the behavior of the Tank T temperature. Figure 2 (left) shows an example of the Tank T behavior during a slow pre-cooling mode. We can consider the system is to be sufficiently cold when the Tank T temperature has decreased after being raised when the slow pre-cooling started. It takes around 4 to 5 hours to decrease (see Figure 2 (left)).
The fast+slow pre-cooling allows us to reduce the slow pre-cooling time by initially fast pre-cooling the first part of the transfer line and then transition transitioning to the slow pre-cooling. Figure 2 (right) shows an example of the Tank T behavior of a slow pre-cooling that followed a fast pre-cooling. It is observed that the Tank T temperature drops significantly faster when a fast pre-cooling is initially performed reducing the slow pre-cooling time to about 1 to 2 hours. The efficiency of this procedure is consistent with the standalone slow pre-cooling efficiency minus 1% given by the initial fast pre-cooling consumption of 4 additional liters of LHe on the Liquifier.
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2. Repeat step 1 reducing the flow by 10 slm SLM until reaching 2 slmSLM. If the pressure increases when the flow is reduced, change it back to the previous value.
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