A versatile 4 K insert for characterization of the superconducting joints

A multi-coil superconducting magnet is the heart of any modern Magnetic Resonance Imaging (MRI) scanner. The superconducting magnet in MRI produces a highly homogeneous field (±5 ppm) and stable field (<0.1 ppm/h) in its imaging volume. The temporal field stability depends on the electrical resistance of the inter-coil joints and the electrical resistance of the joint between the coil and the superconducting switch. To establish the joint technology, a 4 K test rig is required for testing the sample joints. This paper briefly discusses the details of the versatile 4 K insert recently developed at IUAC for the characterization of the superconducting joints using the field-decay measurement technique. It can measure the joint resistance up to ∼10-15 Ω in a straight or spiral joint configuration with lengths up to 150 mm. The maximum current that can be induced on the test coil is more than 600 A for the field-decay measurement. The behavior of the joint resistance can also be studied in the presence of a 1.5 T background field. We have characterized many superconducting joints using this versatile 4 K insert. The joints between two different conductors can also be studied using this 4 K insert. The lowest joint resistance measured is 8 × 10-15 Ω at zero field. The joint resistance is also measured in the presence of the background field.