Improvement in Mechanical Support Structure of a High Field ${\rm Nb}_{3}{\hbox {Al}}$ Common Coil Magnet

The fabrication of a 13 T Nb₃Al common coil magnet is ongoing at KEK. Magnetic simulation shows that opposite direction Lorenz forces are applied to the two layers of the most center coil, where the maximum magnetic field is located. The forces strongly tend to separate the two layers of the coil, which will lead to the damage to the layer insulation and the movement of the superconducting cable. The preload applied at the room temperature with water pressured bladder, together with the thermal contraction stress of the aluminum shell after cool-down provides support to the coil against the Lorenz forces. An improvement in the mechanical support structure of the common coil is presented in this paper. With the improved support structure, the force transfer efficiency from the aluminum shell to the common coil is largely increased, and the sliding boundary of the coil is not required. As a result, the bladder pressure for the room temperature assembly or the thickness of the aluminum shell can be reduced. The stress behavior of the magnet with the new structure is also presented.