Magneto-structural analysis of the fermilab TQC Nb3Sn high gradient quadrupole end region

The Fermilab TQC magnets are Nb₃Sn technological quadrupoles based on the collar-yoke-skin mechanical structure. These magnets, with an aperture of 90 mm, have a design gradient in excess of 200 T/m. In operation the conductor is subjected to forces which tend to pull it away from the poles and endparts to which it is bonded. Given the implications of bond failure for quench initiation, it is of interest to simulate the behavior of these interfaces. The ANSYS general purpose finite element program is used to perform both the magnetic and structural analyses. Interface elements between bonded parts are monitored during assembly, cool down, and excitation, and the birth–death capability of the program is applied to remove from the solution those portions of the interface which experience a tensile stress in excess of a presumed bond failure stress. The cracking of previously bonded interfaces can be tracked graphically over the range of operation. Emphasis will be placed on the details of the magnetic simulation, the implementation of various interface conditions, and the effects (and shortcomings) of material property models.