A microwave device for accelerating electrons includes an electron gun providing an electron beam along an axis in a microwave structure for accelerating the electrons of the beam, an input for the electron beam, an output for accelerated electrons, and a series of coupled cavities along said axis, of central resonant frequency, an input for a microwave signal for excitation of the microwave structure by one of the cavities, a radiofrequency generator providing the excitation microwave signal to the acceleration microwave structure, and a central unit controlling the variation of energy of the electrons at the output of the microwave structure. The radiofrequency generator comprises a frequency control input for changing the frequency of the excitation microwave signal around the central resonant frequency, the change producing a variation of the energy of the accelerated electrons of the beam at the output of the microwave structure.