Parametric study of an augmented railgun

Three different geometries of parallel augmented railguns (circular with one pair of augmenting rails, rectangular with two pairs of augmenting rails, and rectangular with one pair of augmenting rails) have been simulated with the finite-element electromagnetic code MEGA. The mutual inductance gradient M´ and the stress on the rails have been calculated as a function of the geometry and compared with M´ and the rail stress in a simple railgun. Therefore, constant currents were injected in a three-dimensional railgun model with a fixed projectile. The simulations show that the rectangular geometry with one pair of augmenting rails is the best choice for an experimental railgun: M´ is the highest of the three geometries studied and the mechanical structure is the simplest. By investigating the stress on the rails when injecting a pulsed current, we found that a delay between the current injection in the inner circuit and that in the outer circuit can reduce the drag force on the projectile due to the eddy currents induced by the outer circuit current. We show that the outer rails can be attracted or repulsed, depending on the ratio between the current in the inner circuit and that in the outer circuit.