A mechanical analysis of rotating-coil magnetometers

Rotating-coil magnetometers are among the most common and most accurate transducers for measuring the integral magnetic-field harmonics in accelerator magnets. The measurement uncertainty depends on the mechanical properties of the shafts, bearings, drive systems, and supports. In this paper we study the mechanical phenomena (static and dynamic) affecting rotating-coil measurements and propose analysis and diagnostic methods for improving the instrument in terms of material choice and geometrical design. The propagation of uncertainty is investigated on the measured quantities (induced voltages, integrated and developed into a Fourier series, the coefficients of which are know as field harmonics). This results in a consistent framework for the design of a measurement bench for rotating-coil magnetometers. The paper also presents the design of a complete system, including displacement stages, supports, rotating coils, and an angular position system.