Railgun conductor heating from multiple current pulses

A numerical technique for solving current and thermal-diffusion problems in railgun conductors was used to study Joule heating in rails that are subject to multiplecurrent pulses. Copper rails that are 25 mm high by 12.5 mm wide with a 20-mm-square bore and a current pulse with 1-MA peak current and 1-ms pulse width at half maximum were assumed. This combination of parameters is sufficient to accelerate an 80-q projectile to 2-3 km/s with each current pulse. Three parameters were varied in the analysis: the repetition rate or current pulse frequency (3.3 to 100 Hz), the coolant coolant-channel distribution in the rail. Results in the form of plots of rail temperatures as a function of time, are used to illustrate the acceptability or unacceptability of particular combinations of these parameters for operation at steady state. An uncooled rail is not acceptable for steady-state operation. Repetition rates of about 30 Hz are acceptable with the higher coolant heat-transfer coefficient and the best coolant-channel distribution; this includes cooling the rail exterior surface.