A method for controlling egress of gas from a cryogen vessel (12) housing a superconducting magnet (10). A controller (30) receives data indicative of gas pressure within the cryogen vessel a controlled valve (40) controls the egress of cryogen gas from the cryogen vessel (12) and data is made available to the controller, indicating a state of the magnet. Egress of cryogen gas from the cryogen vessel is controlled by operation of the controlled valve (40) by the controller (30) in response to the available data indicating a state of the magnet.
