Testing of a high performance, precision-bore railgun

This paper discusses the results of high-pressure (up to 350 MPa) railgun experiments. The gun is designed both to be capable of high-pressure operation without structural damage and to be readily disassembled for inspection, maintenance and component testing. Considerable effort has been invested to develop techniques to produce and measure smooth, extremely precise (>5µm of variation) bores. We have not deliberately varied bore precision to determine the effect of precision on performance, but our experience suggests that if two otherwise identical railguns, one with a polished, high-precision bore, were fired under identical conditions, the precisely finished gun would achieve a higher muzzle velocity. Very high accelerations have been achieved (>10⁷m/s²). A 2-g projectile has been accelerated to 5 km/s in a 13 mm square-bore gun only 1 m long. Projectiles with an L/D as small as 0.65 have been successfully accelerated. Projectiles with smaller L/Ds have not yet been tested to determine the minimum L/D which can be successfully accelerated. A number of different insulator materials ranging from common float glass to fused quartz have been tested. The best results have been obtained with fused quartz, which shows promise of being reusable. In the course of testing, the importance of gasketing the rail-to-insulator seams to prevent loss of plasma has become apparent. We have made progress in gasket design, but more work is needed. Rail gouging has been a continuing problem. Gouging may be dependent on bore precision, projectile fit, rail mechanical properties, projectile L/D, structural stiffness, operating pressure, velocity, and shape of the current pulse.