Measuring field multipoles in accelerator magnets with small-apertures by an oscillating wire moved on a circular trajectory

Abstract

A method based on an oscillating wire for measuring the field quality in accelerator magnets with small apertures of the order of 10 mm is proposed. The wire is positioned step-bystep on the generators of a cylindrical domain inside the magnet aperture, i.e. its end-points at the stages are moved on a circular trajectory. The amplitudes of the wire's forced oscillations are measured and related to field harmonics by a suitable analytical model. In this paper, the analytical model, the measurement procedure, and the measurement system architecture of the oscillating wire method are presented. The method is validated by comparison with the standard rotating-coil system. A case study on small-aperture, permanent-magnet quadrupoles constructed for the Linac4 injector at CERN is illustrated.

Uncertainty analysis of a vibrating-wire system for magnetic axes localization

“…The influence of the working frequency is also in agreement with previous observations [18], where a marginal instability of the resonance condition was pointed out. This instability led to work at low frequency in the case of the oscillating-wire method, used for multipole measurement [7], where a high stability of the oscillation amplitude is required. In the case of vibrating-wire, where the resonance condition is chosen to privilege sensitivity, the measurement repeatability is improved by working about 1 Hz below the resonance; the slight sensitivity loss is compensated by increasing the wire current.…”

“…It has been used to precisely align and measure the field quality of magnets for particle accelerators [5,7]. Nevertheless, the tight requirements mentioned above involve a substantial improvement of the metrological performance.…”

Performance of the Optimized Mechanical Design of the CLIC Main-Beam Quadrupole Magnet Prototype

“…The oscillating wire is the magnetic measurement method chosen because it proved to be particularly suitable for small aperture magnets [6]. The transverse field harmonics are obtained positioning the wire step by step on K positions (k = 1 .…”

On-field monitoring of the magnetic axis misalignment in multi-coils solenoids

“…While several methods have been developed and successfully applied to the alignment of quadrupole magnets [6], several problems arise from standard methods for solenoids [7,8]. For instance, the single-stretched-wire method, a standard method for finding quadrupole magnets' magnetic axis, has much lower sensitivity when applied to solenoids, because the intercepted transversal field components are significant only at the magnet's ends [9].…”