A model of the beam centroid motion in a linear induction accelerator(LIA) was developed. It calculates the track of the beam centroid under the condition of cell magnet misalignment. The 3D magnetic field distribution is calculated with a coordinate transform. The track of the beam centroid is given by a coupled solution of the beam centroid and envelope equations. Quantitative relation between the transverse displacement of beam centroid and the misalignment of magnets is useful in the installation of magnets and the adjustment of steering coils.

A calculation model of accelerator beam envelope has been developed. It can predict beam envelope in linear induction accelerator from the injector to the final focus region. Its code can easily calculate the effect of various electric and magnetic element parameters on the beam. As calculating examples, the envelopes of 3 kA-beam current under the condition of 40 m long magnetic profiles are given.