Design criteria for brush commutation in high speed traveling wave coilguns

Barrel current in a traveling wave coilgun must be commutated on and off, and remain synchronized with the position of the armature coils. Brushes on the armature can be used to satisfy these two requirements. First, they provide synchronization of the currents by being physically attached to the armature coil. Second, they provide a means of shorting the turns of the barrel so that motion-induced commutation can take place. A set of design criteria is presented for designing a brush-commutated coilgun so as to achieve the required synchronous commutation. The design variables include the barrel coil configuration and its pitch, the armature coil configuration and its number of turns, and the brush length. The number of turns in the barrel undergoing commutation at the same instant in time is directly related to the length of the brush. The results of applying the design criteria to a specific design are presented