Minimization method for accurate position-determination using a position-sensitive Schottky cavity doublet*

Abstract A position-sensitive Schottky Cavity Doublet (SCD) was developed to enhance the accuracy of isochronous mass measurement at the Rare Radio-Isotope Ring (R3) at RIBF-RIKEN, Japan. The aim is to increase the accuracy of position measurement, which is used to correct the momentum spread, thus reducing the uncertainty in the mass determination. The detector comprises a cylindrical reference cavity and elliptical position-sensitive cavity, which uses an offset beam-pipe to create a relation between the Schottky power and horizontal position. The uncertainty in the power response can be improved by minimizing free parameters inside the power equation, providing a second-order correction for the position determination. This requires a large dispersion and momentum spread to effectively characterize the SCD acceptance, which simulations show is achieved when using 76 Zn as a reference isotope. A key parameter to minimize is uncertainty of the impedance map, which relates power to position in the elliptical cavity. We find that an uncertainty in impedance of 0.3 Ω results in a precision equal to that of the current mass measurement method. Additionally, measuring momentum with the SCD enables the removal of other detectors from the beam-line, which drastically reduces the yield of high-Z beams via charge-change interactions.