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The Naval Research Laboratory Materials Testing Facility performs basic research on high-power railguns. The laboratory houses a 6-m-long, 5-cm-bore railgun capable of launching 0.5-kg projectiles at up to 2.5 km/s. The railgun is powered by an 11-MJ capacitor bank comprising twenty-two 0.5-MJ modules. The crow-barred banks can drive up to 1.5 MA in the railgun. The railgun core consists of steel rails with copper backers and epoxy laminate insulators. Aluminum armatures with acrylic bore riders are used for the launch package. Launch data are recorded digitally and analyzed using in-house computer codes. The system design is presented along with typical data. [ABSTRACT FROM PUBLISHER]

The Naval Research Laboratory has developed an automatic electromagnetic launcher system for countermeasure deployment. The launcher operates at 1 Hz and can fire bursts of one to six 44- \mm^2 projectiles. The launcher is controlled from a computer that permits selection of the bank charging voltage and the number of shots. The present experimental setup consists of a railgun, an autoloader, and a rapid charger with computer control. [ABSTRACT FROM AUTHOR]

Properly designed augmented railguns (ARGs) can operate at significantly lower currents and higher efficiency than conventional non-ARGs. This paper analyzes the performance of a two-turn and a three-turn ARG showing the design parameters that are needed to achieve low-current high-efficiency operation. The ARG of this paper has a 40-mm square bore and is 820 mm long. Typical operating currents are from 150 to 300 kA with pulsewidths of approximately 6 to 8 ms. Projectile mass is typically in the range of 130 to 400 g. Projectile velocity is variable from 50 to 250 m/s. Experimental performance is compared with the theoretical predictions of the recently developed electromagnetic launcher (EML) equation. There is a good agreement between measured efficiency and theoretical predictions providing further confirmation of the EML equation. Deviations between measured efficiency and theoretical predictions are attributed to a poor sliding contact. The data also provide further evidence of the recently reported velocity-skin-effect in the contact. [ABSTRACT FROM AUTHOR]

We present efficiency and scaling relationships for dc (i.e., noninduction) constant inductance gradient electromagnetic launchers. We derive expressions for electromagnetic force, efficiency, back-voltage, and kinetic power in terms of electrical circuit parameters. We show that launcher efficiency is a simple function of armature velocity and the launcher's characteristic velocity. The characteristic velocity characterizes the launcher and is the product of two new parameters: the mode constant and launcher constant. Mathematically, the launcher must operate at its characteristic velocity for 50% maximum efficiency. The mode constant reflects the manner in which the launcher is powered and its maximum efficiency. The launcher constant reflects the geometry of the launcher. We consider two modes of operation: constant current and zero exit current operation. We develop the ideal electromagnetic launcher concept and define it as operation at 100% maximum efficiency at all velocities. We also develop the concept of same-scale comparisons, that is, that electromagnetic launcher comparisons should be done with equal bore diameter, launcher length, projectile mass, and velocity. Finally, we present a comparative analysis based on experimental data of same-scale constant gradient electromagnetic launchers for conventional railgun, augmented railgun, and helical gun launchers in terms of the launcher constant, inductance gradient, bore diameter, bore length, system resistance, and armature (i.e., projectile) velocity. [ABSTRACT FROM AUTHOR]