Or at least Friday is nitrogen fill day in my lab and now I've made a liquid nitrogen Dewar, my Lego Spectroscopists can keep the cryogen levels topped up on the Lego NMR Spectrometer (Helium Dewar to follow!)

As a bit more background:

NMR magnets have a superconducting electro magnet coil at their heart, which needs to be at, or near the temperature of liquid helium (-269°C) in order to be superconducting (zero electrical resistance) helium is a finite resource. It is found trapped in certain types of rock and mined, but once released, is so light that it can escape the atmosphere into space. This makes helium a relatively expensive substance and so to slow the rate that the helium boils off and to keep the coil superconducting for as long as possible, the helium container is surronded by a liquid nitrogen (-195.8°C) container and the whole lot is insulated by what is effectively a big vacuum flask. The nitrogen boils off more rapidly than the helium (from the outer, less well insulated container) and so needs to be topped up regularly. Nitrogen isn't a limited resource (78% of the atmosphere) and the liquid (condensing at a higher temperature than helium) is cheaper to produce and easier to handle. For most magnets and in most labs, there is a weekly ritual of topping up the level of nitrogen in the magnet. The nitrogen is transfered from a vacuum insulated tank called a Dewar (named after Sir James Dewar who designed the first vessel of this type).

Some of the most modern systems re-liquify their cryogens with compessors etc. and so in theory may only need to be filled once!

Thanks for all the support, comments and requests for additions and updates. I've got a few things in the pipeline (including an updated console, probe and cryoprobe!) and hopefully if I start making more regular updates I can stir up momentum for more support! 10000 is a very long way to go!