UC Irvine N2 filling procedure (Oxford 800 MHz)

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Liquid N2 transfer line.

Fig. 2 Liquid N2 port. Normal view.

Fig. 3 Liquid N2 port prepared for connecting the transfer line.

Liquid N2 fill in progress. In this picture transfer line nozzle is not wrapped (with a towel) as it should have been. Covering up cold metal parts prevents formation of ice plug over the securing nut and saves thaw time.

filling magnet with liquid N2 and liquid He simultaneously

Duration: ~1.5-2 hrs (starting at 25 % level) + 0.5-1 hr to thaw-off and remove the transfer line.

Equipment

full 200 L liquid nitrogen tank on wheels, non-magnetic, 22psi
liquid nitrogen transfer line (Fig. 1)
non-magnetic wrench to connect transfer line
two plastic tubings to fit exhaust ports
aluminum stair-case ladder on wheels

Procedure

write down level of liquid nitrogen, nitrogen and He boil-off rates
lower the magnet on the antivibration legs by letting out commressed air supporting the magnet
prepare N2 port on the magnet as shown on figure 3
bring the tank (22 psi, 200L on wheels) within ~3-4 m of the magnet
connect transfer line to the tank (using non-magnetic wrench)
open output valve on the tank to cool the transfer line.
as output nozzle of the liquid N₂ line cools, continuously keep wiping off any condensation/frost with towel or thick glove
once liquid nitrogen starts sprouting from the nozzle, close the valve
remove remaining frost from outer surface of the nozzle
insert nozzle into the magnet N₂ inlet port; note the depth of insertion, do not let the nozzle reach maximum depth; if you feel transfer line cannot be driven any lower - pull it upwards an inch or so.
hand-tighten the nut securing transfer line to the magnet N₂ inlet port, while not attempting to support the weight of the transfer line; the latter measure helps prevent leaks of liquid N₂ during the fill
open the output valve on tank, open pressure builder valve
wrap open metal parts of the transfer line with cloth towels - especially the nozzle as it helps prevent accumulation of frost and speeds up thaw-off in the end
watch the increase of liquid nitrogen level on the monitor screen - it should be 0.5-1.0 %/min
close tank outlet valve once liquid starts sprouting from the exhaust tubings
let the nozzle thaw, then remove it, re-attach N₂ exhaust pipe and emergency release valve
restore pressure in the antivibration legs