An apparatus 10 for manipulating the trajectories of moving charged particles. The apparatus includes a grid 14 of laterally spaced side by side elongate elements 16 and means 18 defining a path for charged particles to traverse the grid. The grid is supported and configured for application of a voltage gradient between and/or along the elongate elements, whereby to manipulate the trajectories of charged particles that traverse the grid. A method of manipulating the trajectories of moving charged particles is also disclosed.