Please also open the preset page (Fridge 2x3) to monitor the key parameters:
Each Target Parameter of Fridge 2x3 is explained below:
- In the 1st row and 1st column, the strip chart is related to the chip resistor, which we installed in different locations on the fridge. The purpose of these chip resistors is to track the level of liquid helium in the fridge. When the liquid is at a certain level, say Heat-Ex Bottom (Ohm), it should show 1400 or 1450 Ohm resistance. Usually, we fill the fridge to the Heat-Ex Top (Ohm) and leave it there. But, during a regular, sustainable polarization study, we must keep the Heat-Ex Bottom (Ohm) level.
- The strip chart in the first row and the second column relate to the fridge nose level (in percentage) and the two valves, the Run and Bypass valves, which we usually use to fill the fridge. We can use a Bypass valve when we have to fill the fridge quite quickly. But during sustainable polarization, to replenish the liquid level in the fridge, we have to use a Run valve to keep the level at Heat-Ex Bottom (Ohm).
- The strip chart in the first row and the third column is related to the total consumption or the boil-off at the cryostat. The Main (SLM) target parameter shows the evaporation from the fridge while filling it by opening the Run or Bypass valve. The Separator (SLM) target parameter shows the separator flow we are getting from the magnet reservoir via a U-tube to fill the fridge. The MagRetBypass (SLM) target parameter shows the boil-off from the magnet reservoir. The Total (SLM) shows the sum of the three target parameters.
- The strip chart in the second row and the first column are related to fridge pressure. The Fridge/1000 (Torr) target parameter shows the fridge pressure more accurately when it is above 100 torr. Still, the Fridge/100 (Torr) target parameter shows the fridge pressure more accurately when it is under 100 torr. Suppose the fridge pressure is above 100 torr. In that case, the Fridge/1000 (Torr) target parameter is reliable, and the fridge temperature to the Fridge/1000 (K) target parameter is in the second row and second column. Suppose the fridge pressure is under 100 torr. In that case, the Fridge/100 (Torr) target parameter is reliable, and the fridge temperature to the Fridge/100 (K) target parameter is in the second row and second column.
- The second row and third column show the CAD model of the fridge.
Please read the entire procedure first and then proceed to start filling the fridge:
Please follow the steps to fill the fridge:
- Change the separator flow to 20 SLM (from 7 SLM usually).
In the above picture, click on point 1 THCD-401 to open the VI to control the separator flow. Manually change the value on point 2 in the Change S.P. To 20 and press Enter.
2. Wait for 1.5-2.0 hours.
3. Change the separator flow to 25 SLM. (As shown in Step 1)
4. Change the setting of the gate-valve bypass as follows:
a. The auto control is disabled.
b. The absolute valve position is 0.08 turns.
In the above picture, click on the GV Bypass on point 1 to open the VI to control the GV Bypass.
Click on Point 2 to disable the auto control with pressure.
You can manually change the set point on point 3 by entering 0.08 and pressing Enter, or you can manually Change the set point on point 4 by entering 32 and pressing Enter.
5. Change the setting of the fridge valve system as follows (on Fridge_Valve_Main.vi).
A. The level probe is “CONT” (not “HOLD”).
B. The Interlock with Heat-Ex Top is enabled.
In the above picture, click on point 1, Fridge Valve, to open the VI to change the readout mode.
If the Readout mode is not “CONT” mode, put it on “CONT” mode on point 2.
Check the status of the Interlock with Heat-Ex Top; if it is not on Interlock, toggle the button to put it on the Interlock with Heat-Ex Top mode.
6. Open the bypass valve at 2.0 turns. Confirm that the fridge return flow goes up.
In the above picture, set the Bypass turns at 2, but manually insert 2 and press Enter.
By opening the bypass valve, you will notice the elevation of the Main return flow.
To check the Main Return flow, please see the below strip chart in the 1st row and 3rs column target parameter on the strip chart.
7. Open the bypass valve at 3.0 turns. (As performed in Step 6).
8. Change the separator flow to 30 SLM. (As shown in Step 1)
9. Wait until the Ann-Plate Top resistor goes up to 1400 Ohm, which indicates that the liquid started accumulating. It usually takes 30 minutes from step #3. If it takes longer than 40 minutes, search for unexpected conditions. (Please see the parameter in the above Strip charts (1st row and 1st column Target Parameter Ann-Plate Top (Ohm))).
10. Wait until the nose LHe level reaches 100%. It usually takes 15 minutes from the previous step. (Please see the parameter in the above Strip charts (1st row and 2nd column Target Parameter Nose LHe Level (%))).
11. Wait until the Heat-Ex Bottom resistor goes down from 1400 Ohm and then up. It usually takes 10 minutes from the previous step.(Please see the parameter in the above Strip charts (1st row and 1st column Target Parameter Heat-Ex Bottom (Ohm))).
12. Wait until the Heat-Ex Top resistor goes up to 1400 Ohm, which indicates that the liquid is as high as Heat-Ex Top. It usually takes 10 minutes from the previous step. (Please see the parameter in the above Strip charts (1st row and 1st column Target Parameter Heat-Ex Top (Ohm))).
13. Close the bypass valve.
a. Usually the software interlock sets it at 0.1 turns automatically.
b. Anyway you set it at 0.0 turns manually.
In the above picture, click on Point 1 top open the Fridge_Valve VI, according to Step 12, when the Heat-Ex Top resistor goes to 1400 Ohms the interlock becomes red and set the bypass valve at 0.1 turns automatically.
After that, you can fully close the bypass valve by inserting 0 at point 4 and press Enter.
14. Change the separator flow to 7 SLM.
Manually insert 7 at point 2 to set the separator flow at 7 slm.
15. Change the setting of the gate-valve bypass as follows:
a. The set point for the auto control is 40 Torr.
b. The auto control is enabled.
In the above picture, check the set point which needs to be 40 torr at point 5. If it is 40 torr then toggle the button (Auto Control with Pressure) at point 2, if not at 40 torr manually insert 40 and press Enter and finally toggle the Auto Control with Pressure at point 2.
16. Change the level-probe mode back to “HOLD” if you changed it in step 5.
In the above picture, click on point 1 to open the Fridge valve. Click on point 2 to put the Readout Mode at “HOLD” mode.
Note: At the end of the fridge fill, if the system was in the following configuration, then put the system back into that configuration like:
- If the separator flow before the fridge fill was set at 7 or 11 slm, it should be put back to 7 or 11 slm after the fried fill.
- If the fridge pressure was not set on PID on Auto Control, then there was no need to put it on PID Auto Control, as in step 15.
- If the Readout Mode was at COLD, put it back to CONT mode in step 16.
Filling the Fridge to keep the liquid level at Heat-Ex Bottom (Ohm) during sustainable polarization studies or Microwave studies:
During sustainable polarization studies or microwave studies, the following steps are used to keep the liquid level in the fridge at Heat-Ex Bottom (Ohm).
You only need to open the Run valve at a few turns to keep the liquid level at the Heat-Ex Bottom (Ohm). There are some Optiml Run Valve openings for two situations:
1. When the Microwave is running, and the Liquid level drops down from the Heat-Ex bottom (Ohm), then open the Run valve at 2 turns to replenish the liquid to the fridge to keep the level at the Heat-Ex Bottom (Ohm). When the level reaches Heat-Ex Bottom (Ohm), which you can see when its resistance shows 1400-1450 Ohm, you can leave the Run valve open at 0.65 turn or 0.60 turns. But keep watching so as not to let the liquid level go above the Heat-Ex Top (Ohm). If the Heat-Ex Top (Ohm) starts increasing above 1400 or near 1400 Ohm, lower the Run valve turns from 0.60 or completely close the Run valve.
Please see the corresponding strip charts for Heat-Ex Top and Heat-Ex Bottom in the 1st row and 1st column.
2. When the microwave is not running, the optimal opening of the run valve is 0.55 or 0.50 turns to keep the liquid level in the fridge at Heat-Ex Bottom (Ohm). If the liquid starts rising above the Heat-Ex Bottom, which you can see from the Heat-Ex Top resistance, close the Run valve.
Please see the following pictures of how to Open the Run valve.
In the above picture, click on point 1, Fridge Valve, to open the VI to change the readout mode.
Insert manually the number of turns that you want to open the Run valve and press Enter.