After more hard yakka and some smoothing and cleaning up, things are shaping up better than imagined!
|Behold - the 20K radiation shield!|
(or the outside of it, at least)
|Spec Trek: Into Darkness (ugh don't get me started)|
(the liquid nitrogen is fed into this void)
As can now be seen, this particular super-conducting magnet features an annular liquid nitrogen vessel which is separated from the 20K radiation shield (this shield is another 4-5mm layer of aluminium) by an additional vacuum layer. The single layer of aluminium foil also acts as a radiation shield.
This is quite different to what was exposed in the dissection of a 270 MHz Oxford magnet by JEOL USA Inc. in around 1999 (see right). The design change may be down to the relative ages of the magnets, or may be associated with the higher field strength of our magnet. For field strengths below 300 MHz, it is in fact not necessary for the entire solenoid to be submerged in liquid helium (the vapour is sufficiently cold to maintain the superconducting state). For (lots) more information, see the full story of JEOL's dissection here.