Investigation of the Possibility of Using Turn-by-Turn Measurements to Detect Perturbations in the Magnetic Structure of Accelerators

Abstract

The PCA correction method consists of a global analysis of turn-by-turn data obtained from beam position monitors (BPMs). One of its main advantages is speed of operation and the ability to detect pulsating power supplies. Along with this, a wide range of applications characterizes the PCA method: determination of perturbations of the accelerator magnetic structure, calculation of transport matrix elements and optical functions, and determination of the magnitude of the transverse coupling. A software prototype implementing the proposed correction method was written and tested on the electron-positron collider VEPP-4M for experimental validation. In the experiments, perturbations were introduced one by one into individual elements of the skew-quadrupole and quadrupole corrections. In one case, the excitation of betatron oscillations was carried out by the kick of the inflector. In another case, the oscillations were excited by resonant swing with a depolariser. It was found that, despite the simplicity of practical implementation, the examined method has some nuances that make it difficult to obtain and identify correct results. Nevertheless, it was possible to identify the introduced perturbations of quadrupole and skew-quadrupole corrections. Moreover, it was possible to detect a magnet with low-frequency pulsations by characteristic changes in the estimated invariants. In addition, the possibility of determining the integral coupling parameters in experiments on the observation of resonantly excited eigen modes having the shape of ellipses in the plane transverse to the beam motion axis is considered.