  Vortices in electron beams can manifest several types of topological
phenomena, such as the formation of exotic structures or interactions with
topologically structured electromagnetic fields. For instance, the wavefunction
of an electron beam can acquire a phase vortex upon propagating through a
magnetic monopole, which, in practice, provides a convenient method for
generating electron vortex beams. Here, we show how an electric field must be
structured in order to achieve a similar effect. We find that, much as in the
case of magnetic fields, closed but not exact electric fields can produce
electron vortex beams. We proceed by fabricating a versatile
near-obstruction-free device that is designed to approximately produce such
fields and we systematically study their influence on incoming electron beams.
With such a single device, electron vortex beams that are defined by a wide
range of topological charges can be produced by means of a slight variation of
an applied voltage. For this reason, this device is expected to be important in
applications that rely on the sequential generation and manipulation of
different types of electron vortices.
