Charged particle acceleration and mass separation by oscillating electromagnetic fields

Usually, under forces by the electric and magnetic fields of a uniform-in-space travelling wave, the velocity and energy of charged particles oscillate with no net energy exchange. However, if the phase between the electric and magnetic field is as in standing waves, charged particles can be accelerated. Such a secular term of the particle velocity evolves in a magnetized plasma, when an additional steady magnetic field is present, but also in an un-magnetized plasma, in the absence of such a steady field. In both magnetized and un-magnetized plasma, the direction of acceleration is mass dependent. In a collisional plasma, the acceleration becomes a drift, and the drift velocity decreases with the collision frequency. Interestingly, the direction of that drift velocity is also mass dependent. Alfven standing waves can be used for this process. Possible implications of these processes are in electric propulsion for space vehicles and for plasma mass separation.