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The current 28 GHz Electron Cyclotron Resonance Ion Sources (ECRISs), constructed with Nb-Ti wires and conventional sextupole-in-solenoid or unconventional solenoid-in-sextupole structure, have utilized about 90% of the critical limits of the Nb-Ti wires to achieve maximum operating frequencies of up to 28 GHz. To produce an ECRIS capable of operating at fields required for frequencies of about 45 GHz while maintaining the Nb-Ti wires operating within conductor limits, a Mixed Axial and Radial field System Demonstrator (MARS-D) is being constructed at Lawrence Berkeley National Laboratory (LBNL). This system, which consists of an innovative hexagonal Closed-Loop Coil (CLC) and a set of solenoids, can generate up to 50% higher magnetic fields than the conventional magnet structure while using only about 50% superconducting wire, enabling Nb-Ti wires to be used in the next generation 45 GHz ECRIS. However, the assembly and cooling of such efficient and compact magnets are particularly challenging due to the small radial gap between CLC and solenoids and the small operating temperature margin. To address these challenges, a structure combining a three-section radially split solenoid mandrel with a series of interference-fit reinforcement rings and cooling channels was developed. This paper presents the detailed structure, manufacturing method, assembly procedure, impregnation method, mechanical and thermal Finite Element Analysis (FEA), and cryogenic test plan.
