Modeling and analysis of the current distribution between the brushes of a multiple brush projectile in a parallel augmented railgun

One of the main problems of electromagnetic railguns is the heating of the contact between the current brushes and the rails. One possibility to reduce this heating without reducing the electromagnetic force on the projectile is to apply an exterior magnetic field, as in a parallel augmented railgun. Another possibility is to equip projectiles with multiple current brushes to obtain a better current and thus heat distribution. In a multiple brush projectile launched in a non augmented railgun, the current flows mainly through the last current brush. This corresponds to the path of lowest impedance. If transition of this contact occurs, the resistance of this path will increase and the current will flow mainly through the next current brush. This phenomenon continues until transition has occurred on all the brushes and a good electric contact between the rails is lost. In a parallel augmented railgun, the applied augmenting magnetic field will have an influence on the current distribution in the projectile. To study this influence we developed an analytical model of the current distribution between the different current brushes of a projectile in a non augmented and an augmented rail gun, both with a square caliber of 15 mm X 15 mm. A filamentary approximation of the conductors was used. The heating of the projectile was modeled. In order to evaluate this model, the multiple brush projectile and the rails were modeled with the finite element code ANSYS. The influence of the heating of the projectile has been taken into account and in this model the current brushes have finite dimensions. The current distributions calculated with both models were compared. A parametric study was carried out for projectiles with different configurations of the projectile and for different current profiles in the augmenting and the inner circuit of the railgun.