Center for Laser Applications

Railgun Research

During the academic year 1995/1996 the railgun project was completed. The railgun project was initiated in 1986 and was supported by the Space Defense Initiative Office at a total value of over two million dollars. The objective was to determine the physical mechanisms which limit maximum plasma railgun velocity. This objective was accomplished through an extensive experimental and theoretical research investigation. A number of new diagnostic techniques were developed in the course of this work, including the first spectroscopic measurements of a railgun plasma armature and new methods for analysis of magnetic probe data. These new techniques were implemented on much larger railgun facilities supported by the Department of Defense.

New laboratory railgun designs were conceived and implemented at the CLA laboratories to permit carefully controlled repeatable experiments to be performed. These included the development of full-bore lapping procedures for a railgun barrel and the extensive use of separately augmented railgun barrel structures. Analysis and interpretation of experiments using these facilities resulted in new physical models for the flow in plasma armatures and for the electromagnetic interactions with the railgun structure.

Extensive theoretical analysis of the three-dimensional electromagnetic behavior of railgun structures showed that the fundamental force equation used to evaluate railgun performance was incorrect. Performance estimates were found to be in error from 5 to 50% depending on the type of railgun structure employed. The important thermal effects on the armature force were identified. These effects were identified and quantified using advanced computer simulation codes. The three-dimensional electromagnetic effects were simulated and quantified using MEGA, an advanced electromagnetic code developed at the University of Bath. MAP3, a three-dimensional magnetohydromagnetic (MHD) plasma code was developed at UTSI to simulate the detailed flow in the railgun plasma armature. This was the first time that these complex flows could be simulated, and the simulations showed that the flow was much different than predicted by two-dimensional MHD codes. The crucial effect was the current distribution in the armature which resulted from the diffusion of magnetic fields into the rails. This unexpected flow results in higher viscous losses in the plasma and leads to the formation of secondary arcs which severely limit railgun velocity.

This research project resulted in two Ph.D. dissertations and five Master's theses. Twelve publications in refereed technical journals and numerous presentations at international meetings resulted from this research, including two Best Paper awards.

Investigators: Dr. Dennis Keefer and Dr. Roger Crawford
Sponsor: SDIO/IST