An apparatus and a method to manipulate at least one beam of charged particles are provided. The apparatus comprises two rows of field source members 13 which are disposed periodically at a distance from each other such that there exist planes of symmetry S, S′ with respect to which the field source members 13 are symmetrically disposed. The field has a component which is displaceable in the x-direction. To provide such field, a pattern of source strengths according to the formula F1(x)=Fm(x)+Fc(x) is applied to the field source members, wherein Fm is a component which is substantially independent of the displacement x0 and Fc is a correction component which is dependent on x0.