An electrical bushing structure includes a central conductor (19) designed to have one (26) of its two ends connected to a superconductor element situated in an enclosure (11) at cryogenic temperature, and its other end (25) connected to an article at ambient temperature. An electrically insulating sheath (20) surrounds the conductor over substantially the entire length of the conductor. A metal tube (24) surrounds the conductor over substantially its entire length and is interposed between the insulating sheath (20) and the conductor (19), the tube being mechanically fastened to the conductor close to one of the ends (25, 26) of the conductor, referred to as its first end, and not being mechanically fastened to the conductor close to the other one of the ends of the conductor, referred to as its second end. A space between the conductor and the tube containing a gas. The tube is in electrical contact with said second end of the conductor.