Additive manufacturing and electromagnetic characterization of a "plasma-shaped" cavity for electron cyclotron...

The improvement of electron cyclotron resonance (ECR) ion source performances has traditionally relied on scaling magnetic field strength and microwave frequency. Here, an alternative strategy based on the redesign of the plasma chamber and microwave injection system is proposed. The innovative geometry, named Innovative Resonator Ion Source (IRIS), is derived from the six-branch star iso-density surfaces of electrons confined in a minimum-B field. The structure employs a slotted waveguide, integrated into the cavity walls, which allows enhanced microwave coupling and more uniform power deposition in the plasma core. Electromagnetic simulations predict increased mode density, which possess on-axis electric field profiles with maximum located around the cavity axis in the 14.4-15.4 GHz range, contrary to the electromagnetic modes typical of conventional cylindrical geometries. Two prototypes were manufactured via laser powder bed fusion: a full-scale model for experimental testing and a scaled version with integrated cooling channels to assess manufacturing feasibility. After surface treatment via plasma electrolytic polishing and dimensional verification, the full-scale prototype was experimentally characterized through scattering parameter and on-axis electric field bead-pull measurements for three selected modes, showing excellent agreement with simulations. Vacuum tests demonstrated operation in the 10-6 mbar range after conditioning. These results validate both the IRIS design and the adopted additive manufacturing approach for next-generation ECR plasma chambers.