Optimization & testing of resistive region of hybrid current leads for warm bore conduction cooled superconducting magnet

A 3 Tesla warm bore conduction cooled Superconducting Magnet is developed, installed and being tested at Bhabha Atomic Research Centre, Trombay for mass spectroscopy application. Unlike bending dipole based mass spectroscopy which only selects charged particles, solenoid mass spectroscopy collects, selects and focuses the particles which enables mass spectroscopy with divergent charged particle beams. One of the important sub-systems of Conduction Cooled Superconducting Magnet is current leads. In contrast to conventional current leads, hybrid current leads are made up of resistive part and HTS (High Temperature Superconductor) part. It transports electrical current from a power supply at room temperature to a superconducting magnet at cryogenic temperatures. The resistive element is connected to the HTS element through the intermediate block and heat is intercepted at the first-stage of cooling system. Therefore, heat leak through the current leads is a major factor in cryogenic loads for Superconducting Magnet. Design challenge of current leads involve, reducing cryogenic heat loads by optimization of heat conduction & heat generation (Joule heating). For reducing conduction heat load, area and length of the copper section needs to be reduced and increased respectively. However it increases the Joule heating. Conduction heat and Joule heating optimization thus have contrary requirements. Design of current lead requires dimensional optimization (Length, Cross Section), material selection and thermalization design. Keeping in view the above requirements, design of hybrid current leads is carried out analytically and confirmed with simulations using COMSOL MULTIPHYSICS. This paper details the optimization aspects and comparison between analytical and simulated results. Based on the design, current leads are fabricated and tested in a conduction cooled superconducting magnet. (author)