[en] For short-pulse operation of a resonance electron linac, it is proposed to use an accelerating section based on ring diaphragmatic waveguide with a large angle of particle flight (Θ≅ω₀D/c>π). Particle flight angle is increased through sparser disposition of diaphragms. Such being the case, phase velocity of the first harmonic of accelerating field will exceed velocity of light, therefore, HF-energy is supplied to the section through outlet matching device, and electron acceleration is performed by the first space harmonic of on-coming wave. It is shown that Θ>π transition allows to increase an ultimate accelerated charge while decreasing average acceleration rate. The last disadvantage can be compensated through regeneration or HF-pulse compression system. 4 refs.; 2 figs