A method may include: generating an ion beam from an ion source, the ion beam having an initial direction of propagation; deflecting the ion beam at an initial angle of inclination with respect to the initial direction of propagation; passing the ion beam through an aperture in a magnetic assembly; and generating in the aperture, a quadrupole field extending along a first direction perpendicular to the initial direction of propagation of the ion beam, and a dipole field extending along a second direction perpendicular to the first direction and the initial direction of propagation.