Rail accelerators are superior to classical gas-driven accelerators with regard to attainable terminal velocity, ignition delay variation, and controllability. The behavior is generally described with a system of nonlinear differential equations, which can be solved in many ways. This is done in order to describe an existing launcher, to predict its performance when parameters change, or to estimate the properties of such a system in the design phase. This paper presents a simplified electromechanical system of differential equations in a novel form. This form enables scientists to solve the equations using one of the following software: Scilab, MATLAB, or a similar one. The model is robust and parameter changes have a low impact on the solving time. This makes it a reliable tool for parametric studies. The model comprises pulsed power capacitors, the pulseforming network, cables, and the launcher itself. At first, the electrical part is described with its circuit equivalent and coupled with the mechanical process. Second, the system is analytically transposed to a standard form. This form is then transferred into the simulation software, which solves the equations. It can simply be adapted to other launchers and modified to comprise nonlinear side effects. The simulation results are compared with experimental results from the augmented rail accelerator at the French-German Research Institute of Saint-Louis, France.
The muzzle velocity variation is a parameter of many kinds of accelerators. Actively reducing this value is achieved by observing the motion of the accelerated object during launch and by adjusting the propelling force to achieve the desired velocity. Applying this method to classical gas guns requires a controllable energy source. Experiments with Busy Lizzie type gas-driven accelerators resulted in limited success due to severe energy transfer and timing problems. The railgun overcomes these limitations as it uses an electromagnetic field as propellant being able to transport power with almost the velocity of light. Using multiple independent capacitor modules feeding the railgun enables a flexible release of energy. Results are presented from experimental investigations on the control of the acceleration in an augmented railgun. The observation of the accelerated object's motion is performed using a light barrier system. The output signal is read by a micro-controller that decides at which points in times the capacitor modules will be switched on based on a control algorithm. It is shown that the muzzle velocity variation can be reduced by shifting the switch-on points in time of the capacitor modules.
For symmetric Taylor tests a 2 m long electromagnetic accelerator will be used to accelerate 100 g rods up to 300 m/s. Only a small variance of the muzzle parameters, velocity and exit time, is tolerable. In order to find the most reliable, simple and efficient accelerator type, an axial coilgun, a flat-channel accelerator and an augmented railgun are compared using a lumped parameter model. In particular, the accelerator mutual inductances and their gradients characterize the propulsive forces. The essential advantages of the flat-channel geometry over the axial coilgun geometry are shown. The geometric improvements of the flat-channel accelerator open the way for the augmented railgun suitable and effective for the planned application. To minimize the variance of the muzzle parameters, modular capacitor banks with semiconductor switches allow the dynamic control of the railgun current, in principle.
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