Development of a low energy loss micro-channel plate based position-sensitive detector for the Rare Radio-Isotope Ring

A position-sensitive micro-channel plate type detector has been developed for use in the Rare Radio-Isotope Ring at RIKEN, Japan. It uses secondary electrons emitted from a conversion foil and deflected at 90° to create a position signal. Design constraints included operation in a high-vacuum, a large area to cover the ring acceptance and low beam interaction to reduce energy loss. It must achieve a precision sufficient to measure the in-ring dispersion and perform position diagnostics for tuning the injection. Reducing the time-of-flight of secondary electrons was principal in improving resolution as it reduces their final Gaussian spread. This was implemented by compacting the geometry of the detector and raising the acceleration potential. Electric field homogeneity was also improved by decreasing the electrostatic grid wire pitch from 2 mm to 1 mm. Offline tests with alpha sources and online tests with a 200 MeV/u ⁸⁴Kr beam were conducted, reaching a final average position resolution of $\sigma$ = 1.3 mm. This is sufficient for conducting beam diagnostics in the storage ring.