The importance of three dimensions in the study of solid armature transition in railguns

It is shown experimentally that the main processes first causing breakdown of the sliding solid contact (SSC) carrying large currents are not two-dimensional processes of the velocity skin-effect type, but pinch instabilities developing in the contact interface. Electromagnetic and electrothermal explosive ejection of ionized material of low-mass pinch waists ignite parasite-shunting arcs behind and ahead of the armature under acceleration, Thus one has to speak of transition into arcing mode not of the SSC alone, but of the launch process as a whole. It has been noted that during the transition into the arcing mode the solid armature begins to behave as a hybrid armature of pulling type. At this operation mode, two stable arcs appear, due to pinch cords moving forward along the contact surfaces, which are fixed to both contact surfaces of the armature near their leading edges. Consequently, the armature main body is accelerated under the action of internal tensile forces originating in its leading part where the I x B farces are applied.