Advanced RF cavity manufacturing using multi-material laser powder bed fusion

Abstract Radio frequency quadrupoles (RFQs) are essential components of linear accelerators (Linacs) but remain challenging to manufacture using conventional techniques. Additive manufacturing (AM) offers the potential to lower production costs and enhance RFQ performance. However, vacuum sealing of AM cavities has so far been restricted to concepts without knife edges, limiting Linac applications. We present an RFQ prototype fabricated as a monolithic multi-material structure with a CuCr1Zr inner cavity and a tool-steel outer shell using laser powder bed fusion (PBF-LB/M). Compared to a previously reported prototype, optimized process parameters yielded a relative transition-zone density of about 99.7%, enabling a helium leak rate in the order of $$10^{-8}\mathrm {\tfrac{mbarL}{s}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>8</mml:mn> </mml:mrow> </mml:msup> <mml:mstyle> <mml:mfrac> <mml:mi>mbarL</mml:mi> <mml:mi>s</mml:mi> </mml:mfrac> </mml:mstyle> </mml:mrow> </mml:math> . To enhance the quality factor $$Q_0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>Q</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:math> , the cavity surface was electropolished to reduce surface roughness and subsequently plated with pure copper to increase conductivity. A final $$Q_0$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>Q</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:math> of approximately 3100 was achieved. These results demonstrate significant progress toward vacuum-compatible, high-performance RF cavities produced via PBF-LB/M.