  Electron vortex beams offer unique opportunities for the study of chiral or
magnetic structures in electron microscopes and of fundamental effects of
quantum interference in particle physics. Immersing a cathode in a solenoid
field presents a highly efficient and flexible method for the generation of
vortex electron beams which is utilized at accelerators, but has not yet been
realized in an electron microscope. The conditions for the generation of vortex
beams with quantized orbital angular momentum from an immersed cathode in an
electron microscope are discussed, and general possibilities of this technique
for the production of vortex beams of other charged particles are pointed out.
