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The fast pre-cooling transfer efficiencies are about obtained range from 47-49% which does not allow filling the entire magnet volume using just only one full Liquifier. Nevertheless, higher efficiencies of about 54% can be obtained with the fast pre-cool if the Liquifier pressure is reduced to 3.5 PSI at the expense of nearly 2 hours (~8L) where the Liquifier is not producing while reaching the set pressure. With the fast pre-cooling the last part of the the transfer line is not repre-cooled (see Figure 1). When the GV02 valve is fully open, the fast pre-cooling takes about 4 minutes and consumes 4L. Although the fast pre-cooling has a lower transfer efficiency the procedure could be performed when the magnet needs to be filled immediately and the slow pre-cool hasn't been done because none of the Liquifiers are near full.
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. During the slow pre-cooling, we can estimate when the system is cold enough through the behavior of the Tank T temperature.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 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 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 temperatures drops significantly faster when a fast pre-cooling is initially preformed reducing the slow precooling time to about 1 to 2 hours. This initial fast pre-cooling consumes 4 additional litters of LHe on the Liquifier.
Figure 2: Tank T temperature behavior for slow pre-cooling (left) and fast+slow precooling (right) procedures.
The reported efficiency values were obtained by performing the magnet fills from the seam to the level probe spike.
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Proceed to fill the magnet anytime after the transfer lines are cold. The system is sufficiently cold once the Tank T temperature decreases after opening VJVT (about 5 hours). The figure below shows an example of the Tank T behavior during a slow pre-cooling.
Fast pre-cooling:
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