Before attempting to transfer helium into the PPMS system, be aware of the precautions and hazards associated with liquid helium: the extremely cold liquid and gas can cause serious burns

The following procedure is recommended for transfers when the dewar is low, but not empty, or whenever additional helium is required. There are three different procedures for cold helium transfers, depending upon the level reading. All transfer arrangements are described below.

We have made appointments for the ordering of Helium at the cryogenic department of Hans van Kuyk. Every Tuesday and Friday there will be a vessel available with 90 litres of liquid Helium. When you get the vessel, please book it under Gerrit's account (nr 65, password gerrit). The vessel can stay upstairs. Never empty it completely!

1. Make sure both large and small pumping lines are connected from the probe to the Model 6000 and that the system pump is turned on.

2. Set the system temperature to 3.5K. This will cause the cooling valve to open and turn the impedance heater off. The function of the cooling valve is to allow the system to self-flush the temperature control impedance as the system cools down. Flushing allows the helium gas to carry out contaminants from the warm dewar. When the dewar level has reached 30%, the impedance is covered in liquid, reducing the chance of the impedance becoming blocked with contaminants. Verify that the proper adapters and extensions are installed on the helium transfer line.

3. Vent the pressure from the liquid helium dewar (storage dewar) by opening the gas phase valve to the helium recovery line, via the shortcut on the membrane pomp. This mebrane pump will use helium gas from the recovery line to put pressure on the storage dewar.

4. Slide down the input and output adapters on the PPMS transfer line to just above the attached extensions.

5. Remove either one of the dewar relief valves. These are the valves located on either side of the probe head. .

6. Open the liquid access port of the liquid dewar. Insert the transfer line, input end first, into the liquid dewar and lower it very slowly. Continue until you see an exhaust plume from the output end.

7. With the exhaust plume visible, carefully insert the output end into the PPMS dewar. Lower the transfer line as far down as it will go.

8. On the input side (liquid dewar), raise the end up off the bottom about 1/4 of an inch, or be sure that the end piece of the transfer tube ghas a small hole a few cm's above the end.

9. Start the transfer by switching on the mebrane pump and (partially) close the shortcut.

10. Continue the transfer at a slow, steady rate until the level reaches 25-30%. Note: At this point, the flow rate should be between 2 and 2.5 liters per minute. The transfer may be increased, the cooling valve may be closed, and you may set the desired system temperature.

11. Continue the transfer until the level is 97-100%, then open the shortcut and switch off the membrane pump. Wait until the pressure from the liquid helium dewar (storage dewar) is relieved.

12. Remove the PPMS transfer line and install the dewar relief valve.

from the Model 6000 Controller, 2 possbilities:

1. *Press the Control key to enter the Control Menu.

• Select item 1, Interactive Control, and press Enter.
  
• Select item 0, Fill Dewar, and press Enter.
  
• After 5-10 minutes, purge the sample space two or three times by

2. from the Multivu program go to <utilities> and <Helium fill>

When the current helium level is below 20% but not zero or negative, follow the same procedure as previously given except for the following change: When the helium level reaches 25-30% (in step 2 of the previous section) close the Cooling Valve from the Diagnostic/Gas Controls menu.

1. Make sure both large and small pumping lines are connected from the probe to the Model 6000 and that the system pump is turned on.

2. Vent the pressure from the liquid helium dewar (storage dewar) by opening the gas phase valve to the helium recovery line, via the shortcut on the membrane pomp. This mebrane pump will use helium gas from the recovery line to put pressure on the storage dewar.

3. Slide down the input and output adapters on the PPMS transfer line to just above the attached extensions.

4. Remove either one of the dewar relief valves. These are the valves located on either side of the probe head.

5. Open the liquid access port of the liquid dewar. Insert the transfer line, input end first, into the liquid dewar and lower it very slowly. Continue until you see an exhaust plume from the output end.

6. With the exhaust plume visible, carefully insert the output end into the PPMS dewar. Lower the transfer line as far down as it will go.

7. On the input side (liquid dewar), raise the end up off the bottom about 1/4 of an inch, or be sure that the end piece of the transfer tube has a small hole a few cm's above the end.

8. Start the transfer by switching on the mebrane pump and (partially) close the shortcut..

9. Continue the transfer until the level is >90%, then open the shortcut and switch off the membrane pump. Wait until the pressure from the liquid helium dewar (storage dewar) is relieved.

10. Remove the PPMS transfer line and install the dewar relief valve.