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, l argely unexplored. Accordingly, this paper includes a discussion of th e theoretical models used to predict the inductance gradient, the tran sient 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 inductanc e gradient of L'(R) = 0.52 mu H / m compares very well with the measur ed value of 0.522 mu H / m. The existence of an inductance gradient ef ficiency 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 waveshap es are in good agreement with observations close to the bore center. F or radial distances greater than a foot, measured peak fields exceed p redictions by a factor of two to three. This issue is being investigat ed.