Conceptual development of a novel ultra-thin and transparent 2 T superconducting detector solenoid for the Future Circular Collider

In the frame of the ongoing Future Circular Collider (FCC) Study, a novel ultra-thin and maximum radiation transparent solenoid for next generation particle detectors is under development. Actually, two versions providing 2 T and 3 T for the FCC-ee and FCC-hh detectors, respectively, are engineered, but here we report on the 2 T version only. Essential aspects of the design are presented. The mechanical and thermal stability of the cold mass is investigated. New, very high-yield stress Al-stabilized NbTi/Cu conductors are required to allow a 0.4 * X$_0$ radiation thickness. For conductor production, welding of dissimilar aluminum alloys will be necessary. Electron beam and friction stir welding techniques were tested to connect the Ni-doped pure Aluminum stabilizer to the very high-yield strength Al-7068 alloy. The welding results and their applicability are presented and discussed. The proposed conduction-based cold mass cooling scheme using heat drains, and quench protection were analyzed and results are presented.