Bore lifetime experiment

Although the need for railgun bore lifetime measurement has been established for some time, to date there have been no serious attempts at quantification of the anticipated lifetime of a railgun bore surface. The US Air Force (AF) is meeting this challenge with an in-house bore lifetime experiment that compares four different bore insulator materials and lay-ups in a controlled test environment. Initial testing has established a G-9 material as a baseline for comparison. Each of the four insulator test series consists of a low current checkout shot followed by a ten shot series of plasma armature firings with peak pressures of about 30 ksi and currents of the order of 750 kA. The test sequence produces erosion that is easily measured both as bore growth during the test series and as post-test component mass loss. Typically, the rails lost almost twice as much mass as the insulators, but volumetrically, about three times more volume of insulator material was removed compared to eroded volume of copper from the rails. The loss of copper from the rails is highly nonuniform, as might be expected in a round bore railgun. Mass loss and bore growth data from all four insulator test series are compiled as a gauge of bore lifetime. The railgun performance on a typical shot is given along with a tabulation of the coarse shot parameters for each test in all four series.<>