The main goal of the electromagnetic simulations is to find whether the electromagnetic perturbations have an effect on the beam electrostatic instability, thus increasing the degradation of the beam quality. A detailed investigation, using the full electromagnetic model, has been conducted and presented in [9]: only the essential physical results of this investigation are summarized below.
As expected, backward TE and TM waves can easily be excited in the
lossless cylinders considered here, leading to large spreads of the
perpendicular velocity 
. The parallel
velocity spreads 
however are
comparable to those found in the electrostatic case. In addition, the
electrostatic perturbations can be identified in the electromagnetic
simulations, but do not seem to be affected by the electromagnetic
perturbations.
Electromagnetic simulations with a magnetic taper have been performed
as well, showing that the magnetic gradient can suppress the
electromagnetic instability
when the excited frequency is not close to the cut-off ( 
).
For the particular case of the gyrotron shown in Fig. 7a, it
is found that the magnetic field gradient in the beam tunnel impedes
the excitation of the backward waves.
Although the electromagnetic perturbations can induce very large values
of , they can easily be suppressed in the beam
tunnel by introducing absorbers on the wall and/or by tapering the wall, unlike
the electrostatic perturbations.