Design and fabrication of a 5 T NbTi solenoid magnet cooled by a closed-cycle G-M cryocooler

This paper presents the superconducting solenoid magnet (SSM) concept, design and construction solutions for a prototype aimed for laboratory applications, which may generate a high magnetic field (5 T) in the central region of the solenoid - the “warm channel”. NbTi wire is used for the field winding. The SSM is contained in a cylindrical case to be kept at safe temperature working conditions by a Gifford-McMahon closed-cycle cryocooler with two cooling stages (50 K and 4.5 K). Mathematical modeling and numerical simulation are used to size thermally the apparatus and to evaluate the “quality” of the magnetic field. Along this line, the thermal loads for the two cooling stages of the cryocooler are evaluated. Two-dimensional models may not produce accurate results so full 3D heat transfer analysis was performed. The pumping power required to keep the SSM within safe operational limits obtained by numerical simulation is in good agreement with available sizing and experimental data.