  Earlier, the authors found a mechanism for the sequence of short relativistic
electron bunches, which leads to resonant excitation of the wakefield, even if
the repetition frequency of bunches differs from the plasma frequency. In this
case, the synchronization of frequencies is restored due to defocusing of the
bunches which get into the bad phases with respect to the plasma wave. However,
in this case, the bunches are lost, which as a result of this do not
participate in the excitation of the wakefield. In this paper, numerical
simulation was used to study the dynamics of electron bunches and the
excitation of the wakefield in a magnetized plasma by a long sequence of short
bunches of relativistic electrons. When a magnetic field is used, the
defocussed bunches return to the region of interaction with the field after a
certain time. In this case, the electrons of the bunches, returning to the
necessary phases of the field, participate in the excitation of the wakefield.
Also, the use of a magnetic field leads to an increase of the frequency of the
excited wave relative to the repetition frequency of bunches. The latter
increases the time for maintaining the resonance and, consequently, leads to an
increase of the amplitude of the excited wakefield.
