Challenges in extracting pseudo-multipoles from magnetic measurements

Abstract

Extracting the coefficients of Fourier-Bessel series, known as pseudo-multipoles or generalized gradients, from magnetic measurements of accelerator magnets involves technical and mathematical challenges. First, a novel design of a short, rotating-coil magnetometer is required that does not intercept any axial field component of the magnet. Moreover, displacing short magnetometers, step-by-step along the magnet axis, yields a convolution of the local multipole field errors and the sensitivity (test function) of the induction coil. The deconvolution must then content with the low signal-to-noise ratio of the measurands, which are integrated voltages corresponding to spatial flux distributions. Finally, the compensation schemes, as implemented on long coils used for measuring the integrated field harmonics, cannot be applied to short magnetometers. All this requires careful design of experiment to derive the optimal length of the induction coil, the step size of the scan, and the highest order of pseudo-multipoles in the field reconstruction. This paper presents the theory of the measurement method, the data acquisition and deconvolution, and the design and production of a saddle-shaped, rotating-coil magnetometer.

An Induction-Coil Magnetometer for Mid-Plane Measurements in Spectrometer Magnets

“…Common solutions to this problem are the filtering of the concerned frequency components or their damping with respect to a known signal to-noise ratio. The latter approach is referred to as Wiener filtering and it has been applied to the deconvolution of rotating coil measurements in [7]. However, all signal filtering or post-processing is either neglecting some frequency components or using prior knowledge for their determination.…”

New Possibilities for Testing the Service Life of Magnetic Contacts

“…To know when the magnetic contact closes so that it is activated, it is necessary to connect a signaling device to it. In the absence of a signaling device, it is possible to use a complete installation of an electrical security system with a control panel, with which we can know when the contact was activated [14][15][16][17].…”