Friction and ablation measurements in a round bore railgun

During the last two years a new round bore railgun has been developed at the Lehrstuhl fur Raumfahrt-technik of the Technische Universitat Munchen TUM (Technical University Munich) in order to investigate friction and electrodeablation effects. This paper describes the experimental determination of the friction and ablation effects. The one-dimensional model for the description of the accerelation of the projectile includes both mechanical friction of the projectile, the viscous arc drag and the electrode ablation effects. The first section gives a description of the experiments, detailed information about the test facility (capacitor bank, crowbar switch. inductive coil etc.) together with the plasma diagnostics. The second section describes the theoretical friction and electrode-ablation model. The mechanical friction model depends on projectile velocity and the dynamic normal pressure between the projectile and the bore walls. A new non-linear electrode-ablation model is also discussed, where ablation depends on two parameters : a) charge transportation between the electrodes b) electromagnetic force impulse from = current) After a short description of the electromagnetic Model, that is necessary in order to determine rail current, crowbar current and inductance gradient, a comparison of experimental results with the theory is given in the final section. The results indicate, that the ablation effect is the main drag work, which reduces the ideal projectile velocity in the range of 10% - 15%.