[en] The dynamics of charged particles in the field of H-waves of a circular waveguide in the presence of a uniform magnetic field is considered. The equations of motion of a particle in the wave field under cyclotron resonance conditions are derived, and the width of resonances is found. The conditions for the resonant interaction between charged particles and the wave are determined. The motion of particles in a standing-wave field (in a resonator) is studied. It is shown that, when several waveguide modes are excited, regimes can occur in which the particle motion becomes stochastic. These regimes are characterized by efficient plasma heating. The results obtained are of interest for plasma heating and can be used in designing charged-particle accelerators and microwave oscillators