Influence of rail resistivity and rail height on armature edge erosion at current ramp-up

Avoiding transition is an important issue for railguns launching solid armatures. At the start stage of railgun launching with current ramp-up, the appearance of aluminum coating tends to be concentrated on the out sides of rails, which indicates current concentration on the edge of armature. In this paper, using finite element code ANSYS, numerical simulations of armature´s current density distribution with rails of various resistivity and heights were conducted. The results show that: (1) current concentrates on edges of armature tail; (2) the current density on edge of armature tail can be reduced by increasing rail resistivity and/or decreasing rail height. In launch experiments in 20mm square caliber railgun, rail material having different resistivity, such as 98%Cu-1%Zr-1%Cr alloy, brass and non-magnetic steel are investigated. Different heights of rail such as 50mm and 30mm are investigated, too. The results show that higher resistivity and lower height of rails have comparatively lighter armature edge erosion at current ramp-up. Based on the work, improved rail structure is proposed.