  The conception of High Power Linac developed in Russian accelerator centres
is based on the use of independently phased SC resonators with quadrupole
lenses between them. The type and parameters of the resonators as well as
focusing structure are varied along the linac to optimise beam dynamics and the
characteristics of the linac. The beam evolution in the linac was studied by
simulation in 3D accelerating and focusing fields by computer code DYNAMION.
  The simulation includes all nonlinearities of external fields and space
charge forces. Estimations of particle losses in the beam based on analysis of
the spectral properties of particle trajectories were carried out.
