Beam position monitor for superconducting post-linac in RAON

The Rare-isotope Accelerator complex for ON-line experiments (RAON) is an accelerator for heavy ions, such as uranium and oxygen. To correct the beam trajectory in the post-linac with low- β, we developed a beam position monitor. In the post-linac, the beam is accelerated from 0.5 MeV/u to 18.5 MeV/u, and each bunch has an electric charge of less than 10 pC. To achieve higher signal strength and better linearity, we investigated stripline- and button-type beam position monitor (BPM) and designed the BPMs with CST Particle Studio. We have fabricated a button-type BPM. We tested 10 BPMs by using a wire test stand to achieve the characterization of each BPM, including the calibration factor with single-pass H electronics of I-Tech. The developed wire test stand has a stretched wire and is movable in the 2D plane with servomotors. In this paper, we present the results of the design, fabrication, and off-line test of a button-type BPM for a low- β, heavy-ion beam.