Superconducting magnets must be operated at liquid helium temperature. Consequently, they require the use of some cryogenic apparatus in addition to the magnet itself. A liquid helium dewar, a means of mounting the magnet in the dewar, a power supply, a liquid helium level meter/sensor, and a helium transfer tube are basic and necessary.
Dewars supplied by AMI are constructed from non-magnetic materials with copper and aluminum radiation shields. All non-demountable joints are inert gas welded providing a rigid, mechanically strong dewar for long and reliable use. All joints are checked with a helium leak detector at every stage of construction, and vacuum integrity is guaranteed for one year. The completed dewar is temperature cycled and tested to confirm that it meets AMI's high standards for quality.
Many of our liquid helium dewars utilize liquid nitrogen shielding for reduced liquid helium consumption. In these cases, the vacuum jackets of the nitrogen and helium reservoirs are connected via a common vacuum pumping port through the radiation shield. Where liquid nitrogen shielding is undesirable, a vapor shielded dewar can be provided with multilayer superinsulation, reducing the radiation heat load of the helium reservoir to a very low value.
Dewars are generally supplied with a reliable bellows sealed evacuation valve, a safety pressure relief valve and provisions for mounting a thermocouple gauge for monitoring the dewar vacuum. The dewars can be provided with a mounting flange, lifting lugs and other options to meet the customer's handling and interface requirements.
AMI offers standard dewars with our superconducting magnet systems. Or if your application requires, we will be happy to provide a custom designed dewar to meet your needs.
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