MRI Magnet Cryostat

A cryostat is used in MRI machines.
They are designed to hold a liquid cryogen, particularly liquid Helium, which is kept in a liquid state with minimal evaporation. The liquid helium is designed to keep the superconducting magnets in their superconductive state. The superconductivity of the wire bobbin used in these machines will maintain its magnetism after the current is removed from the system if and only if the temperature of the bobbin is kept cool by using liquid helium. The bobbin is immersed in liquid helium and is kept cool because of the cryostat.

Cryostats are manufactured with two vessels, one inside the other. The one used in MRIs is built with an outer vessel that is evacuated and an inner vessel containing liquid helium. The outer vessel acts as a thermal insulator as well as a heat removal device. The use of a cold head and a crycooler combination takes thermal energy away from the outer vessel, keeping the system even colder. While liquid helium is most commonly used, older devices use liquid nitrogen for the outer vessel and liquid helium for the inner vessel.

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