Future Pathways of Additive Manufactured RF Launcher Design

A high field side lower hybrid multijunction launcher at 4.6 GHz and n_||=^-2.7 constructed for DIII-D is expected to improve current drive efficiency compared to low-field-side launch scenarios in similar plasma discharges. Additive Manufacture (AM) enabled designs that reduce circulating power with a traveling wave power divider and aperture impedance matching. Laser powder bed fusion enables novel launcher designs that cannot be achieved by conventional manufacturing. GRCop-84 and GRCop-42 copper alloys resist annealing at 900°C while maintaining high thermal conductivity and strength superior to Glidcop and CuCrZr. Hot isostatic pressing consolidated all remaining internal voids increasing >99.8% density to 100%. Chemical or chemical-mechanical polishing refined internal surface roughness to 0.3µm Ra, better than extruded copper waveguide. Brazing, E-beam and laser welding to join launcher and waveguide segments are compared. Poloidal power dividers were printed monolithically with pentagonal waveguides modified for AM that self-support overhanging elements with a chamfered roof while maintain RF tuning properties and low return loss. Launcher designs that may be monolithically printed are explored.