Magnet Support Stand and Lambda Plates

Magnet support stands are designed to suspend superconducting magnets in liquid helium dewars with the minimum input of heat to the helium. The structure of the support stand uses fiberglass or stainless steel support tubes and copper radiation baffles to minimize thermal conduction and radiation heat transfer into the liquid helium.

The addition of a lambda plate to the magnet support stand allows superconducting magnet operation below 4.2K. Typically, the field strength of a superconducting magnet can be increased by more than 10% if the operating temperature is reduced from 4.2K to 2.2K. A lambda plate will maintain the magnet temperature at reduced temperatures for extended periods of time and is a cost effective way to obtain higher magnetic fields.

The lambda plate assembly typically includes a dewar top operated throttle valve and vacuum pump port. The throttle valve allows a small amount of liquid helium to enter a low pressure vacuum region within the lambda plate. The low pressure, vacuum region flashes the liquid helium to a low temperature gas which cools the lambda plate. Heat is transferred from the liquid helium remaining in the magnet well section of the dewar until an equilibrium temperature is reached. The low pressure vacuum region is maintained with a vacuum pump attached to the vacuum pump port. For proper lambda plate operation, the dewar must be designed with a thermally isolated magnet well section.

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