Linear particle accelerators (Linacs) are primarily composed of radio frequency cavities (cavities). Compared to traditional manufacturing, Laser Powder Bed Fusion (L-PBF) holds the potential to fabricate cavities in a single piece, enhancing Linac performance and significantly reducing investment costs. However, the question of whether red or green laser PBF yields superior results for pure copper remains a subject of ongoing debate. Eight 4.2 GHz single-cell cavities (SCs) were manufactured from pure copper using both red and green PBF (SCs R and SCs G). Subsequently, the surface roughness of the SCs was reduced through a chemical post-processing method (Hirtisation) and annealed at 460 °C to maximize their quality factor ($Q_0$). The geometric accuracy of the printed SCs was evaluated using optical methods and resonant frequency ($f_R$) measurements. Surface conductivity was determined by measuring the quality factor ($Q_0$) of the SCs. Laser scanning microscopy was utilized for surface roughness characterization. The impact of annealing was quantified using Energy-Dispersive X-ray Spectroscopy and Electron Backscatter Diffraction to evaluate chemical surface properties and grain size. Both the SCs R and SCs G achieved the necessary geometric accuracy and thus $f_R$ precision. The SCs R achieved a 95% $Q_0$ after a material removal of 40 µm. The SCs G achieved an approximately 80% $Q_0$ after maximum material removal of 160 µm. Annealing increased the $Q_0$ by an average of about 5%. The additive manufacturing process is at least equivalent to conventional manufacturing for producing cavities in the low-gradient range. The presented cavities justify the first high-gradient tests.

The enormous potential of additive manufacturing (AM), particularly laser powder bed fusion (L-PBF), to produce radiofrequency cavities (cavities) has already been demonstrated. However, the required geometrical accuracy for GHz $T{M}_{010}$ cavities is currently only achieved by (a) avoiding downskin angles $<{40}^{\circ }$, which in turn leads to a cavity geometry with reduced performance, or (b) co-printed support structures, which are difficult to remove for small GHz cavities. We have developed an L-PBF-based manufacturing routine to overcome this limitation. To enable arbitrary geometries, co-printed support structures are used that are designed in such a way that they can be removed after printing by electrochemical post-processing, which simultaneously reduces the surface roughness and thus maximizes the quality factor $Q_0$. The manufacturing approach is evaluated on two $T{M}_{010}$ single cavities printed entirely from high-purity copper. Both cavities achieve the desired resonance frequency and a $Q_0$ of approximately 8300.

Linear particle accelerators (Linacs) are essential for numerous applications in industry, medicine, and research. However, their use is often constrained by high investment costs, which are largely driven by conventional manufacturing methods. Studies have shown that additive manufacturing (AM) has the potential to significantly reduce these costs while simultaneously enhancing Linac performance. This study investigates this potential for the production of radio-frequency quadrupoles (RFQs), one of the most important Linacs for ion acceleration. For the first time, a multi-material RFQ prototype was fabricated using multi-material (MM) laser powder bed fusion (PBF-LB/M) AM, integrating the copper alloy CuCr1Zr for the internal cavity and tool steel (1.2709) for the outer shell in a single manufacturing step. The prototype’s design features six ConFlat® (CF) flanges for sealing without O-rings, highlighting the advantages of MM AM in simplifying assembly and enhancing functionality. Experimental evaluations included assessments of geometric precision, surface roughness, microstructural integrity, vacuum performance, resonance frequency (f_R), and quality factor (Q₀). The results demonstrated the successful application of MM PBF-LB/M for RFQ production, achieving a vacuum pressure below 8.3 ∙ 10^–8 mbar in the prototype. However, challenges in geometric precision and material transition zones necessitate further process optimization. This work underscores the potential of MM PBF-LB/M to address limitations in mono-material AM, particularly for Linac applications. Future developments, such as enabling pure copper processing and improving thermal and mechanical performance, could establish MM PBF-LB/M as a transformative technology for advanced Linac designs, paving the way for enhanced Linac applications.

Achieving high dimensional accuracy in the build direction remains a critical challenge in laser-based powder bed fusion of metals (PBF-LB/M), particularly for taller components. This study investigates the application of the standardized Z-artefact defined in ISO/ASTM 52902:2023 to evaluate and correct vertical dimensional deviations in AlSi10Mg parts. Benchmark artefacts were produced without Z-scaling and measured using a structured light 3D scanner. A linear trend of increasing undersizing with build height was observed across two build jobs, indicating a systematic Z-error. Based on the reproducible average deviation, a shrinkage compensation factor of 1.0017 was derived and applied in a third build job using the same processing parameters. This correction reduced the root mean square error (RMSE) from over 100 µm to below 25 µm and improved the achievable ISO tolerance grades from IT 9–11 to IT 5–9. The approach proved effective without requiring changes to process parameters. However, local surface features such as elevated edges and roughness remained dominant sources of deviation and are not captured in step height-based evaluations. Overall, this study demonstrates a practical, standard-compliant method to improve vertical dimensional accuracy in PBF-LB/M, with potential applicability to industrial quality assurance and future extension to more complex geometries.