[en] To study beam dynamics while electron beam injection into electron-ring accelerator analytical expressions for E and H waves excited coherently by the beam are derived. Time intervals both before the moment of ring beam formation when EH-field energy storage takes place and after the closing, when dampling of excited wave modes takes place, are considered. Estimation of excited wave modes indicated that at the ring particle number of excited wave modes indicated that at the ring particle number of approx. 10¹³ the energy loss does not effect characteristics of equilibrium motion. The influence of excited field on transverse motion of particles in a beam was considered. Initially the beam was consistent and the Coulomb field was considered, then it was affected by excited fields. The calculation indicated that the action of excited field leads to a modulation of the beam mean square dimension which is weak when parameters of the system do not correspond to resonance ones. Under certain conditions the parameter resonance possibly appears or the increase of excited field amplitude is possible when the revolution frequency is equal to harmonics of resonator eigenfrequency. However, in practically important cases the danger of resonance phenomenon is not large, since it appears only at high harmonics, and due to the chamber small Q-factor excited fields appeared fade quickly