CHARACTERIZATION OF SUPERCONDUCTING CABLE FOR K-500 SUPERCONDUCTING CYCLOTRON MAGNET COIL

An experimental set-up has been designed and developed for the electrical characterization of NbTi multifilamentary composite cable at liquid helium temperature under magnetic field up to 7 Tesla. The cable has been used to make K500 superconducting cyclotron magnet coil at Variable Energy Cyclotron Centre, Kolkata. The superconducting critical current is the most important parameter in the design and operation of magnet. The constant electric field (0.1 µvolt/cm) criterion is used to define critical current. The critical current is measured in different magnetic fields, which is applied perpendicular to the direction of current. The critical current is measured taking sample from different spools. As the available pieces of cable are not long enough, there would be at least five number of joints in the winding. Joints are made in-house on the coil winding machine by brazing copper substrate and soft soldering the superconductor elements of the cable. The 100mm lapping length is kept between superconductors in the joint. Joint resistance being a continuous disturbance must also be made minimum as possible. Therefore it is required to standardize procedure for superconducting jointing for minimum resistance and sufficient mechanical strength to withstand the tension, during winding of the coil. Therefore experimental set-up has been designed and developed to carry out the tests. Test results show high critical current density with good filament uniformity indicated by its high quality index. Joints were made inhouse on coil winding machine and test results indicate that they have acceptably low resistance and carry sufficient current.