  The magnetic perturbation due to the ferromagnetic test blanket modules
(TBMs) may deteriorate fast ion confinement in ITER. This effect must be
quantified by numerical studies in 3D. We have implemented a combined finite
element method (FEM) -- Biot-Savart law integrator method (BSLIM) to calculate
the ITER 3D magnetic field and vector potential in detail. Unavoidable geometry
simplifications changed the mass of the TBMs and ferritic inserts (FIs) up to
26%. This has been compensated for by modifying the nonlinear ferromagnetic
material properties accordingly. Despite the simplifications, the computation
geometry and the calculated fields are highly detailed. The combination of
careful FEM mesh design and using BSLIM enables the use of the fields
unsmoothed for particle orbit-following simulations. The magnetic field was
found to agree with earlier calculations and revealed finer details. The vector
potential is intended to serve as input for plasma shielding calculations.
