WHY IS THE HELIUM BOIL-OFF HIGHER THAN NORMAL ?
1.WEATHER FLUCTUATES The weather plays a major role in how fast or how slow liquid helium boils off. Low atmospheric pressure will elevate the helium boil-off. High atmospheric pressure will reduce the helium boil-off. This is normal. A helium gas flow meter is the best way to monitor the effects of weather. 2.NITROGEN VESSEL IS DRY Check to see if there are ice formations on the two ports that exhaust boil off from the nitrogen vessel. If there is no ice present, use the helium thumper tube to check if there is liquid nitrogen (LN2) in the nitrogen vessel. Heating the tip of the thumper tube before inserting it into the bottom of the can , will give a positive reading if it comes in contact with liquid nitrogen. If no LN2 is present, add some. 3.VACUUM HAS DETERIORATED Check to see if the sample is cold or iced in the shim stacks. If this condition is present remove the shim stacks. If ice formation occurs in the entire room temperature bore tube, the vacuum within the magnet cryostat
