Definition of the large enough size of the contact area between armature and rails in railguns

It is an important goal to get larger contact area between armature and rails in the design and operation of railguns. However, oversize contact area may not be so necessary. Most of the current in the railgun will only flow in part of the contact area even the whole flank surface of the armature contacts the rails. So if part of the armature flank surface does not contact the rails, the maximum value of the current density remains almost the same as that with the whole surface contact. It is addressed in this paper what size is large enough from the view of current distribution and the maximum current density. Calculations are also done to analyze the factors affecting the size. Generally, 20% of the armature flank surface can be regarded as the large enough size of the contact area for the certain structure of railgun analyzed in this paper.