Additive Manufacturing of Side-Coupled Cavity Linac Structures from Pure Copper: A First Concept

Compared to conventional manufacturing, additive manufacturing (AM) of radio frequency (RF) cavities has the potential to reduce manufacturing costs and complexity and to enable higher performance. This work evaluates whether normal conducting side-coupled linac structures (SCCL), used worldwide for a wide range of applications, can benefit from AM. A unit cell geometry (SC) optimized for 75 MeV protons was developed. Downskins with small downskin angles α were avoided to enable manufacturing by laser powder bed fusion without support structures. SCs with different α were printed and post-processed by Hirtisation (R) (an electrochemical process) to minimize surface roughness. The required accuracy for 3 GHz SCCL (medical linacs) is achieved only for α>45∘. After a material removal of 140 µm due to Hirtisation (R), a quality factor Q0 of 6650 was achieved. This corresponds to 75% of the Q0 simulated by CST®. A 3 GHz SCCL concept consisting of 31 SCs was designed. The effective shunt impedance ZT2 simulated by CST corresponds to 60.13MΩm and is comparable to the ZT2 of SCCL in use. The reduction in ZT2 expected after Hirtisation (R) can be justified in practice by up to 70% lower manufacturing costs. However, future studies will be conducted to further increase Q0.