Determination of current distribution in EM gun armature by leastsquares fitting of BSi (small-induction) coilvoltage

The electromagnetic (EM) plasma rail-gun current distribution was determined by fitting (using the method of least squares) the voltage induced on small induction (B_Si) coils to a derived function model. The voltage function model was derived using the Biot-Savart equation. The model was derived assuming that the current flowed in sheets perpendicular to the rails. The sheets of currents varied in time and in the rail direction but were assumed to be constant (at a given time) perpendicular to the bore direction. The plasma current distribution in the bore direction, the initial length, and expansion characteristics of the plasma were determined from B _Si coil voltage measurements taken at short time increments. Fitted parameters correlate well with measurements taken by other sensors