Helium fill procedure

Helium fills should be done every 24-25 weeks. 

  1. Place an order with the vendor  for 100 L liquid helium at least 3 days in advance of the planned fill date.
  2. Gather supplies.  Some supplies may be in the under-stair compartment in the NMR lab.  Others are upstairs in the Chemistry Stockroom and labs. 
  • cryo gloves
  • goggles
  • aluminum ladder
  • helium gas tank
  • helium regulator
  • helium flow ball guage
  • connectors for helium gas to liquid helium Dewar (including threaded to nipple connector)
  • paper towels
  • flutter tube
  • meter stick
  • helium transfer line with proper fittings for attachment to supply Dewar
  1. Measure initial He level in supply Dewar using flutter tube and meter stick and record the initial volume in the log book.  A supply Dewar helium level chart (inches to liters conversion) is here.
  2. Loosen magnet helium check valve (located at the center of the helium manifold at the rear of the magnet.  Remove and plug the opening immediately with a loose wad of paper towels.  (The goal is to prevent air flow back into the magnet.)
  3. Loosen the magnet helium fill plug (right side of magnet).
  4. Position the helium supply Dewar close to the magnet and under the raised soffit in the ceiling (to allow sufficient height for the helium transfer line). 
  5. Precool the helium transfer line by slowly inserting the stinger (longer tube on the transfer line) into the supply Dewar, eventually below the liquid level.  As He escapes from the other end of the transfer line, wipe the outside repeatedly with a glove to keep frost from forming.  When plume increases and then turns dark gray, the tube is cool and liquid helium is flowing. 
  6. While taking care not to touch the sample carousel or break and tubes with the helium transfer line, quickly remove the plug on the magnet at the helium fill port and slowly insert the helium transfer line as far as the marking near the top of the tube (about 2.5 " from the top), in coordination as the other person lowers the stinger further into the supply Dewar.   Some venting of the supply Dewar may occur.   Remove the paper towel plug from the magnet helium manifold, if it has not blown out already. 
  7. Gently tighten the small black collar where the helium transfer line enters the magnet. 
  8. Adjust the helium gas flow rate so that the ball guage is about half way up the scale, to provide small positive He pressure for the transfer.   A gentle plume of helium should be exiting from the rear of the magnet helium manifold. 
  9. The fill takes 30-90 minutes.  Do not leave the magnet unattended during the fill. 
  10. The magnet is full when liquid oxygen begins to drip from the magnet helium manifold and when the vent plume dramatically increases. 
  11. Loosen the small black collar where the helium transfer line enters the magnet. 
  12. In coordination with the person managing the supply Dewar, remove the helium fill tube from the magnet and immediately replace the black plug on the magnet, and pass the transfer line to the assistant. 
  13. Immediately replace the paper towel plug at the back of the helium manifold, then within a few minutes, replace the check valve.
  14. Check and gently tighten the collars for the magnet helium check valve and fill port.  As the magnet helium manifold warms to room temperature over the next 10-30 minutes, check and gently tighten these fittings as needed.
  15. Measure the helium volume remaining in the supply Dewar and record it in the log book, along with the total volume used. 
  16. Record the fill in the online log book
  17. Remove all PLU-owned fittings from the supply Dewar.  Notify the vendor that the liquid helium Dewar is ready for pickup. 
  18. Return all supplies to their storage locations. 

Note:  Instructions for doing helium and nitrogen fills are also found in the Bruker cryostat manual.