Transition in a rail gun system, namely, the phenomenon of solid contact turns into arcing contact, is undesirable because it is associated with severe damage to both armature and rail. The current downslope (−di/dt) transition is one of the most significant transition mechanisms for C-type solid armatures. In this article, considering velocity skin effect (VSE) and magnetic diffusion processes in armature and rail, a simplified 1-D electromagnetic model is used to illustrate –di/dt effect and verify the occurrence of eddy current. However, further simulation with a 3-D model shows that the electromagnetic force caused by the negative net current in the armature’s tail is not the main cause of transition. In addition, a noncontact area between armature and rail is set up to enhance the eddy current, but the resulting reversal Lorentz force is not strong enough to lift off the armature tail from the rail. A set of launching experiments was also carried out using three types of armatures with different tail structures in a 20 mm $\times30$ mm rectangular caliber rail gun. The results show that low-voltage transitions occur when the driving current drops to approximately 90% of its peak value during the downslope.

中文翻译：

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C型固体电枢轨道炮下坡低压过渡试验与分析

轨道炮系统中的转变，即固体接触转变为电弧接触的现象是不希望的，因为它与电枢和轨道的严重损坏有关。当前下坡 (-di/dt) 过渡是 C 型固体电枢最重要的过渡机制之一。在本文中，考虑电枢和轨道中的速度趋肤效应 (VSE) 和磁扩散过程，使用简化的一维电磁模型来说明 –di/dt 效应并验证涡流的发生。然而，3-D 模型的进一步模拟表明，由电枢尾部的负净电流引起的电磁力不是转变的主要原因。此外，在电枢和导轨之间设置了非接触区以增强涡流，但由此产生的反向洛伦兹力不足以将电枢尾部从轨道上抬起。在 20 毫米×30 毫米矩形口径轨道炮中，还使用具有不同尾部结构的三种类型的电枢进行了一组发射实验。结果表明，当驱动电流在下降过程中下降到其峰值的大约 90% 时，就会发生低电压转换。