Multipole-field measurements by sampling oblong apertures of accelerator magnets

Oliver Köster,Stephan Russenschuck,Oliver Boine-Frankenheim

doi:10.1016/j.nima.2017.01.001

Abstract

The rotating search coil is a commonly used tool to measure magnetic fields of accelerator magnets. The coil intercepts the magnetic flux at a radius given by the dimensions of the measurement shaft that comprises a set of search coils for the analog bucking of the main signal from the dipole field component. For magnets of a rectangular aperture with large aspect ratio (>3:1) the cylindrical domain covers only a portion of the magnet bore. As the field representation is dominated by measurement errors outside that cylindrical domain, a sampling technique is required. The method presented in this paper trades the precision in the measurements against the precision in the shaft positioning and arrives at a multipole representation that covers the entire bore of the magnet.

Highlights

Magnetic field measurements are of fundamental importance in every accelerator project
We present the combination of three rotating-coil measurements on the mid-plane of a normal-conducting dipole magnet
The combination of the three measurements yields a field synthesis in oblong magnet apertures, which is more accurate than the extrapolation from a single measurement

Summary

Introduction

Magnetic field measurements are of fundamental importance in every accelerator project. Magnetic measurements are essential to study dynamic effects, such as combinations of iron hysteresis and 3D eddy-currents, which are still a challenge in magnetic field simulation. The magnetic field of accelerator magnets is commonly described by its main field component and the higher-order field errors. This representation is an analytic function with socalled multipole coefficients [1]. These coefficients are determined by a Fourier series expansion of one integrated field component along the design trajectory. This representation is strictly two-dimensional as the magnetic field is integrated along the search coil that covers the magnet extremities and the fringe-field region

Methods

Results

Conclusion