A Rotating-Coil Magnetometer for Scanning Transversal Field Harmonics in Accelerator Magnets

Pasquale Arpaia,Gianni Caiafa,Stephan Russenschuck

doi:10.1038/s41598-018-37371-3

Pasquale Arpaia, Gianni Caiafa + Show 1 more

Open Access

https://doi.org/10.1038/s41598-018-37371-3

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Abstract

This paper presents a rotating-coil magnetometer that was designed and validated for scanning local transversal field harmonics, required for extracting so-called pseudo-multipoles in accelerator magnets. The magnetometer consists of four layers of flexible printed circuits with a track thickness of 40 μm. The design aimed at maximizing the sensitivity factors for field harmonics up to order 13 and at a compensation ratio for the main component in the same range of what is achievable with standard rotating coils. Key innovative features of the induction coil are the shape for minimizing the sensitivity to the longitudinal field component and the manufacturing technology. The design, the uncertainty analysis of the manufacturing tolerances, as well as preliminary application results are presented.

Highlights

For magnetic measurements of accelerator magnets, the induction coil magnetometer is still the best transducer in terms of linearity, repeatability, reliability, and accuracy
We propose a new concept of a short, rotating-coil magnetometer that does not intercept the longitudinal field component
The scaling laws derived from the integrated (2D) field harmonics in accelerator magnets cannot be used in the 3D case, because these field harmonics do not constitute a complete, orthogonal function set of the 3D Laplacian

Summary

Introduction

For magnetic measurements of accelerator magnets, the induction coil magnetometer is still the best transducer in terms of linearity, repeatability, reliability, and accuracy. The field distributions at the magnet extremities cannot be developed into Fourier series (i.e. the classical field harmonics), because the trigonometric functions do not constitute a complete orthogonal function set of the field solution. One possibility is to measure the longitudinal profile by mapping the magnet bore with a 3D Hall sensor mounted on a displacement stage or by using magneto-electric flux gate or absolute magnetometry12,13 Another solution is to use a translating-coil scanner on the magnet mid-plane. Another solution is to use a translating-coil scanner on the magnet mid-plane14 In the latter case, the transversal resolution (and the highest order of the field harmonics) is limited by the track widths of the single coils. In the Section “Results”, the sensor design, the computation of the coil-sensitivity factors, the uncertainty analysis of the main coil parameters, the sensor production, and the validation experiments are presented

Methods

Results

Conclusion