Effect of Mutual Flux Linkage Between Stages on the Projectile Motion in a Multistage Induction Coilgun

In the multistage operation of an induction coilgun, the time- varying magnetic flux generated due to the excitation of the first stage magnetically links with the coils in the subsequent stages and induces emf across their terminals. The magnetic flux linkage and the induced emf depend on the distance between the stages. This induced emf tries to circulate a current through the coils in the subsequent stages, if allowed to flow by such means of Pulsed Power Source (PPS) connection with the coils i.e., it depends on the winding direction (clockwise or anti-clockwise) of the coils and the connection of the crowbar diode in the PPS circuit. If crowbar diode is connected in parallel with the capacitor bank then the series main switch resists this induced flow of current through the coil, but if crowbar diode is connected in parallel with the coil in accordance to its winding direction then induced current flows through the coil. In this paper, the effect of this induced current on the motion of the projectile inside a multistage induction coilgun has been analyzed taking different lengths of the hollow projectile of fixed mass and outer diameter. The results of each case have then been compared with that of a single stage coilgun. Analyses have been made using the 2D transient solver of ANSOFT Maxwell software package with excitation (two 252 μF capacitors charged at 2 kV) given only for the first stage. Only two stages have been considered since farther stages will have negligible magnetic flux linkage with the first stage. For each projectile, distance between two stages has been varied starting from 2.8 cm to 14.8 cm with a linear step of 1 cm. The results show that projectile motion is slightly effected in multistage depending on the distance between stages and the length of the projectile. The results will be helpful for maintaining a suitable distance between stages in the multistage design of an induction coilgun.