Light-induced drift of optically active atoms in a buffer gas is a consequence of the unequal diffusive frictions suffered by the excited and the ground-state atoms. This drift can be used to create an “optical piston", in which the active atoms are pushed forward by light through the semipermeable membrane of the buffer gas. Normally, optical piston effect is studied when the active atoms are neutral in a confined one-dimensional situation. We present a detailed theory of this phenomenon when the active atoms are charged and a magnetic field is applied for “tuning” the direction as well as the magnitude of the drift, thus removing the necessity of confinement. Our study is in different geometries of the light beam and the magnetic field, first in the weak collision model, and then for the strong collision and the Boltzmann-Lorentz models. © 2001 The American Physical Society.