Magnetic field measurements on small magnets by vibrating wire systems

A new method based on vibrating wire to measure field multipole is presented. The magnet multipoles are assessed by positioning the wire in different points on a circle inside the magnet aperture and measuring the amplitude of wire vibrations. An analytical model relates vibration amplitudes to multipoles. Results of simulation tests aimed at analyzing the model performance are reported. Preliminary experimental validation results on small permanent magnets for the new linear accelerator Linac4 at European Organization for Nuclear Research (CERN) are shown.

I. Introduction

The vibrating wire method (VWM) is devoted to the magnetic axis alignment in high-order magnets [1]. The physical principle is based mainly on the Lorentz law: when an AC current flows through a wire, a force proportional to the magnitude of the local transverse field component is exerted. The frequency is tuned to have a stationary oscillation. An optical sensor acquires the oscillation parameters in order to calculate the magnetic field. When the wire is positioned close to the magnetic center, the wire vibration amplitude decreases accordingly. The VWM is appreciated for its high accuracy in locating magnetic centers of high-order magnets [2]–[3]. A further advantage of VWM is its capability of finding the magnet axis in limited spaces.