Design, development and testing of 1.5 tesla superconducting magnet for compact MRI

Magnetic Resonance Imagining (MRI) is the biggest commercial application of superconductivity. MRI is a noninvasive powerful diagnostic tool used by medical community for examination of soft tissues diseases such as tumors in cartilages, musculoskeletal, deformities in CTL spine etc. A 1.5 Tesla multi coil superconducting magnet is designed and developed for compact MRI applications for human extremities such as wrist, ankle etc. The developed superconducting magnet is cooled by two stage Pulse Tube Cryocooler in a closed cycle mode and hence do not require liquid Helium for its operation. The heat removal capacity of a cryocooler is limited to 1.5 W at 4.2 K which makes thermal design quite challenging in nature. The multi coil superconducting magnet is designed for uniformity better than 10 ppm in a Diameter of Spherical Volume (DSV) of 160 mm. Nonlinear integer optimization such as fmincon and Nomad algorithms were used to achieve the required uniformity. Developed superconducting magnet has a working bore of 300 mm and a length of 700mm. Spatial magnetic field uniformity is achieved by deploying multi coil design (6 main coils & 2 buck coils). Nb-Ti wire 1.65mm x 1mm is used for magnet development. Temporal stability of the magnetic field is obtained by operating the magnet in persistent current mode. Persistent current joints and switches for this magnet were developed and tested for its rated current. The developed superconducting magnet system is integrated and is being tested for its thermal performance. (author)