Our 500 MHz NMR machine quenched itself today 🙁 Here is an awful quality photo I took of the aftermath.
To make things worse, our other machine (300 MHz one) has been out of action since late last year, so we now have no NMR access whatsoever … for any non-chemists out there, this is bad, VERY bad!
I did some YouTubing and found this video of an MRI machine quenching itself (MRI and NMR are very similar instruments).
[youtube width=”350″ height=”292″]http://youtube.com/watch?v=1R7KsfosV-o[/youtube]
The NMR machine was full of liquid helium. The quenching involved the liquid helium evaporating very rapidly. Here’s a video about the properties of liquid helium and a video of a liquid helium fountain.
Question about Quench… Is a quench a sudden loss of vacuum in the container the liquid helium is in? My limited understanding of an MRI is the following…MRI magnets are usually a superconducting type of magnet. The magnet is made by a coil of wire wrapped around a cylinder/bore. When an electric current is passed through the coil there is a magnetic field generated. The wire in a superconductor is bathed in liquid helium (or other cryogens) at about -450C. I’ve heard that the liquid helium is kept under a vacuum state preventing it from becoming a gas.
The quench CAN be caused by a sudden loss of vacuum, although the reverse could also be true, the sudden quench could crack the dewar causing the sudden loss of vacuum.
The lowest temperature possible is -293 deg. C (or close to it). The liquid helium is not kept under a vacuum, but the insulating dewar surrounding it contains a vacuum to prevent heat loss (no energy losses due to convection). In fact, placing anything (including helium) under vacuum would cause it to become gaseous, the exact opposite of what you suggested.
That makes much more sense now, thank you for your response.