Experimental characterization of electromagnets for particle accelerators

The paper analyses two measurement procedures of magnetic field in electromagnets for particle accelerators. In these devices, it is of interest the magnetic field distribution, in the neighborhood of their axis. This distribution is not measured directly, but by using the measurements of magnetic flux density, in a finite number of points selected by users. Based on these measurements, an analytical method is used to determine field variation in the circular aperture of electromagnet, and to extract the coefficients of their multipole (harmonic) expansion. Experimental characterizations, by using measurements along radius and along aperture periphery are analyzed and compared. It is proven that the circular measurements are more robust, because the radial ones leads to a weak conditioned problem, which is not well-posed, in the sense of Hadamard.