Experience with PSI’s Main Ring Cyclotron Long Radial Probe

A Long Radial Probe is a device used to measure the transverse beam profile in a cyclotron along its radius. The current iteration of the probe was installed in the PSI Main Ring Cyclotron in 2022. After a successful start, the probe encountered issues due to strong coupling with RF fields leaking from the cavities, which resulted in the breakage of the carbon fibers. A series of corrective measures were attempted, but the initial results were inconclusive. This paper discusses the challenges faced and presents the experiments and thermal calculations that provided insights into the RF heating issue.