Mechanical Design of the Superconducting Magnet for the 28 GHz ECR Ion Source ASTERICS

ASTERICS is an Electron Cyclotron Resonance (ECR) ion source designed by CEA, GANIL, and LPSC for the NEWGAIN project in France. The design of the Nb-Ti superconducting magnet is inspired from two magnets built for 28 GHz ion sources (VENUS and FRIB ion sources) and is composed of a sextupole inside three solenoids to confine the plasma. The main improvement in terms of magnetic design comes from an increase of the plasma chamber radius from 71.85 mm to 91 mm aiming at increasing the metallic beam yield at both 18 and 28 GHz. This change in magnetic design leads to an increase of Lorentz forces, impacting the design of the mechanical structure. Like the FRIB ion source, the architecture uses an aluminum shell-based support structure with bladders and keys to compress the sextupole azimuthally, and endplates for its axial compression. The bladders and keys allow a disassembly of the sextupole coils, and an adjustment of the coils pre-stress. The solenoids are wound under tension around an aluminum mandrel acting as a shell for the sextupole pre-load. Interfaces between solenoids and mandrel are designed to allow detachment and low friction sliding during excitation. The scale-up of the support structure, to address the dimension increase, is presented here. The 2D and 3D mechanical models developed to perform the mechanical analysis and the results obtained are detailed along with the preliminary assembly process.