Abstract
The rotating search coil is a precise and widely used tool for measuring the magnetic field harmonics of accelerator magnets. This paper deals with combining several such multipole measurements, in order to cover magnet apertures largely exceeding the diameter of the available search coil.The method relies on the scaling laws for multipole coefficients and on the method of analytic continuation along zero-homotopic paths. By acquiring several measurements of the integrated magnetic flux density at different transverse positions within the bore of the accelerator magnet, the uncertainty on the field harmonics can be reduced at the expense of tight tolerances on the positioning. These positioning tolerances can be kept under control by mounting the rotating coil and its motor-drive unit on precision alignment stages. Therefore, the proposed technique is able to yield even more precise results for the higher-order field components than a dedicated rotating search coil of larger diameter. Moreover, the versatility of the measurement bench is enhanced by avoiding the construction of rotating search coils of different measurement radii.
Highlights
Magnetic field measurements are required at different stages of any accelerator project; during the magnet prototyping phase to validate the magnet design and production process, and during the series production to guarantee the magnet-to-magnet reproducibility and the follow up of the manufacturing
In this paper we present the combination of several measurements of a rotating coil
Accurate measurements of the field harmonics in accelerator magnets require the construction of a dedicated rotating-coil shaft of the largest possible aperture
Summary
Magnetic field measurements are required at different stages of any accelerator project; during the magnet prototyping phase to validate the magnet design and production process, and during the series production to guarantee the magnet-to-magnet reproducibility and the follow up of the manufacturing. Often measurements are required to check hysteresis effects and eddy-currents, which are difficult to compute with finite-element methods. This re-parametrization with respect to the angular position relaxes the requirements on the homogeneous motion of the motor drive unit. Accurate measurement of the field errors relies on shafts with the largest possible diameters in order to maximize the signal-tonoise ratio. The novelty of the proposed method lies in an oversampling procedure using smaller shafts, which yields the same or even better measurement accuracy by acquiring field information at different transverse shaft positions
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