  Free electrons can possess an intrinsic orbital angular momentum, similar to
those in an electron cloud, upon free-space propagation. The wavefront
corresponding to the electron's wavefunction forms a helical structure with a
number of twists given by the \emph{angular speed}. Beams with a high number of
twists are of particular interest because they carry a high magnetic moment
about the propagation axis. Among several different techniques, electron
holography seems to be a promising approach to shape a \emph{conventional}
electron beam into a helical form with large values of angular momentum. Here,
we propose and manufacture a nano-fabricated phase hologram for generating a
beam of this kind with an orbital angular momentum up to 200$\hbar$. Based on a
novel technique the value of orbital angular momentum of the generated beam are
measured, then compared with simulations. Our work, apart from the
technological achievements, may lead to a way of generating electron beams with
a high quanta of magnetic moment along the propagation direction, and thus may
be used in the study of the magnetic properties of materials and for
manipulating nano-particles.
