What is Quenching?

Each super conducting magnet contains a large amount of liquid Helium and liquid Nitrogen.

They are normally kept stable in the liquid phase ( ~ 270C and 200C below zero ) and well isolated below their boiling temperature via layers of high vacuum concentric tanks(stainless non-magnetic steel) of the magnet body structure.

However, when a loose metallic object (such as an office chair with metal frame) is placed within the strong field region ( ~ 15 feet), it will be sucked and attached to the magnet.

The contact deforms all the layers of protection which then creates thermal conductance to the very cool liquids in the inner tanks of the magnet.

The super cool liquid boils rapidly and expands several hundred times in volume inside the confined space of the metal tanks.

The pressure build up pushes large volumn of a gas and liquid mixture from the exhausted vents to all directions. Once the magnet coil is no longer fully immerged in liquid Helium, the large current is discharged from the coil, then generate more internal heat to enhance stronger melt down. This rapid collapse of the supper conducting magnetic field with the uncontrollable boil off of cryogens is called "Quenching".

The malfunction expresses itself as a loud whooshing sound and the lab will be filled up most in gas nitrogen and helium. None of them are toxic but they are not life supporting neither. Contact of  the super-cold liquid with skin could result in body injury or death.

Last update: June 6, 2008 yfl