SOLUTION FOR THE 3-DIMENSIONAL RAIL GUN CURRENT DISTRIBUTION AND ELECTROMAGNETIC-FIELDS OF A RAIL LAUNCHER

Rail guns generate electromagnetic signatures that contain frequencies extending from quasi-dc to tens of kHz. The characterization of these fields for electromagnetic compatability concerns remains, however, largely unexplored. Accordingly, this paper includes a discussion of the theoretical models used to predict the inductance gradient, the transient behavior of the currents produced in the rail gun structure, the dynamical generation of the external fields, and a comparison of the theoretical model with experimental data. The predicted rail inductance gradient of L'(R) = 0.52 mu H / m compares very well with the measured value of 0.522 mu H / m. The existence of an inductance gradient efficiency factor, E(o), is demonstrated, with a derived value of 0.75. This produces an effective inductance gradient of L' = E(o) L'(R) = 0.39 mu H / m which leads to a predicted muzzle velocity of 525 m/s that is within 5% of the measured value. Predicted magnetic field waveshapes are in good agreement with observations close to the bore center. For radial distances greater than a foot, measured peak fields exceed predictions by a factor of two to three. This issue is being investigated.