  Accelerator magnets made from blocks of permanent magnets in a zero-clearance
configuration are known as Halbach arrays. The objective of this work is the
fusion of knowledge from different measurement sources (material and field) and
domain knowledge (magnetostatics) to obtain an updated magnet model of a
Halbach array. From Helmholtz-coil measurements of the magnetized blocks, a
prior distribution of the magnetization is estimated. Measurements of the
magnetic flux density are used to derive, by means of Bayesian inference, a
posterior distribution. The method is validated on simulated data and applied
to measurements of a dipole of the FASER detector. The updated magnet model of
the FASER dipole describes the magnetic flux density one order of magnitude
better than the prior magnet model.
