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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 Liquefier 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 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 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 LiquifierLiquefier.
Figure 2: Tank T temperature behavior for slow pre-cooling (left) and fast+slow precooling (right) procedures.
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2. Open VJVA/B, open VJVT and close VPC.
Note: Liquifier Liquefier A/B should be on Liquify mode. If at the time of starting the slow pre-cooling the Liquifier Liquefier A/B is on Idle mode, start the slow pre-cooling and when 4L are consumed on the Liquifier Liquefier then change it to Liquify mode.
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2. After the FMR has stabilized, set the Liquifier Liquefier A/B to "Manual + Idle", open SV501A/B (inlet valve), and set FC501A/B at 45 SLM. Ensure the outlet valve SVNA/B is closed and the cold heads of the Liquifier Liquefier are off.
3. When the magnet level reaches 48%, open VPC, close VJVA/B, close VJVT.
4. Set the Liquifier Liquefier A/B back to "Auto+ Liquefy".
5. Enable the Pressure PID auto control of the MagRetBypass valve at 0.9 psi.
Post-filling
Monitor the Liquifier Liquefier A/B pressure until the cold-head temperatures are below 5.5 K ensuring the Liquifier Liquefier A/B pressure doesn't go above 9 psi:
1. If the Liquifier Liquefier A/B pressure rises, change the outlet Flow to 60slm on "Settings" and wait until the Dewar pressure is between 6-7 psi and the inlet flow is not zero.
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Note: Always confirm on the Liquifier Liquefier screen whether the outlet flow on FCA/B gives what you set it to. If not, press the "Idle" button and then followed by the "Liquefy" button immediately after.
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