Abstract: A shutter (36) is provided for controlling a beam, or current, of charged particles in a device such as a thyratron (10). The substrate (38) defines an aperture (60) with a gap (32) which is placeable within the current. Coils (48) are formed on the substrate (38) adjacent the aperture (60) to produce a magnetic field for trapping the charged particles in or about aperture (60). The proximity of the coils (48) to the aperture (60) enables an effective magnetic field to be generated by coils (48) having a low inductance suitable for high frequency control. The substantially monolithic structure including the substrate (38) and coils (48) enables the entire shutter assembly (36) to be effectively located with respect to the particle beam.