Helium Fill

Prior to filling

o Fill in the Logbook. Turn on the sensor (switch to the left) and record the date and He level and He flow in the logbook. Leave the sensor on during the helium fill to know the level of helium during the fill. Be sure to turn off the sensor after the fill is completed (switch to center, all lights off).

o Measure the liquid He level in the transfer tank.

Preparation for filling.

o Close the emergency release valve on the liquid helium tank.

o Connect the He gas cylinder to the gas port on the liquid He tank.

o Remove the He flow tubing (clear hose at the top of the NMR) from the exhaust port and place a paper towel into the hole to keep air from getting in (to prevent condensation in the magnet). Beware, the clamp holding it in place is magnetic – do not let it fall into the magnet!

o Prepare the transfer line. Take the helium transfer line off the rack on the wall. The helium transfer line is the one with two pipes that are different lengths, with a flexible tube in the middle. At the top of the NMR, next to the He level sensor cable is the He fill port. It has a cap and a release valve on it. Unscrew the cap and replace the center release valve in the fill port (to prevent condensation in the magnet). Put the cap, o-ring, and washer onto the shorter end (of the helium transfer line) until it reaches the black tape.

o Cool the transfer line. Insert the long end of the transfer line into the liquid helium tank making sure that you’ve got a tight seal. Gas will come out of the other end. Eventually, when the line is cold, you’ll see a white flame coming out of the transfer tube (that is liquid He). Raise the transfer line so that it still has a tight seal with the tank, but the end of the line is no longer in the liquid inside the tank. Now you’re ready to fill.

Filling the magnet.

o Insert the transfer line into the magnet’s He fill port and screw on the cap. Be sure that both sides of the transfer line are raised and lowered at the same time.

o Once the fill port has been sealed, the gas will be exiting the exhaust port. Most of the time there will be enough pressure to push the paper towel out but if there is not then the paper towel will need to be pulled out.

o Fill the magnet slowly! If the exiting gas is billowing gently 2-3ft from the exhaust, then you’re filling at the right rate. If the gas is exiting more vigorously-its to fast!. If there is negative pressure, then air will get sucked into the magnet and create an ice blockage –something to avoid! To fill faster: create more pressure in the tank. To fill slower: reduce pressure in the tank.

o To create more pressure in the tank: use the He gas cylinder to force gas through the liq. He tank (via it’s gas port). Do not exceed ~5psi He gas pressure, and do not exceed 10-1l on the attached flow meter.

o To reduce pressure in the tank: close the He gas port and/or open the emergency release valve (normally ~5psi).

o Fill until liquid He comes out of the exhaust port (or the He tank is empty).

When the white flame appears.

o A 2-3” white flame will appear at the exhaust port when the magnet is full.

o Reduce pressure in the tank.

o Unscrew the cap on the shorter line and remove the transfer line from both the magnet and transfer tank simultaneously.

o Turn of the He gas cylinder and disconnect it from the transfer tank.

o Place the release valve back into the fill port.

o Clean off the exhaust port with a paper towel so that there is no ice left.

o After a min or two, replace the He flow tubing and tighten it in place. Beware, the clamp holding it in place is magnetic – do not let it fall into the magnet!

o Take off the o-ring and cap off the shorter line (you might have to warm up the line a little with a gloved hand). Replace the cap, washer, and o-ring on the release valve and tighten it down on the magnet’s fill port.

Post fill details.

o Measure the liquid He level in the transfer tank. Calculate how much liquid He was used during the fill and enter that information in the logbook. Turn off the He level sensor (switch to center, all lights off).

o Be certain that the logbook is completely filled out, the He level sensor is turned off, the main He gas cylinder valve is closed, and the magnet’s fill port and exhaust ports are properly sealed.

o After the exhaust port warms up (about a half an hour after the fill) retighten the clamp.

Measure the liquid He level in the tank. You’ll need to make three measurements.

1) Mark #1: Hold your thumb over the end of the thumping stick and push the stick inside the tank. When the top of the helium is found, a thumping sensation will occur on your thumb. Mark the place on the stick and take the stick out to measure the position from the bottom.

2) Mark #2: mark the stick when it is inserted all the way to the bottom of the tank.

3) Mark #2-Mark #1 = He level (see chart on wall for conversion to liters, depends on size of tank).