A superconducting device comprises a vacuum chamber and means to evacuate the vacuum chamber. A base plate is provided within the vacuum chamber and first, second and third cylindrical walls extend from the base plate. The second and third cylindrical walls are arranged coaxial with the first cylindrical wall. A first chamber is defined between the first cylindrical wall and the second cylindrical wall, a second chamber is defined between the second cylindrical wall and the third cylindrical wall and a third chamber is defined within the third cylindrical wall. A superconducting wire is arranged within the second chamber and a cryogenic insulating material is arranged within the second chamber to encapsulate the superconducting wire. A material having a high specific heat capacity is arranged within the first chamber and there are means to cool the base plate.