R.C. Zowarka

Predicted versus actual performance of the model scale compulsator system

Performance testing of the model-scale CPA was completed at the University of Texas Center for Electromechanics. A major part of the project was the development of design and simulation codes that would accurately represent the performance of pulsed alternators. This paper discusses the components of the system and its operational sequence. Details of the performance simulation model are presented along with test data. The test result is compared to the predicted data.

Experimental results from CEM-UT's single shot 9 MJ railgun

A 10-m-long, 90-mm bore railgun has been designed and fabricated. During the test program, a number of solid armatures and projectile packages have been tested in a 50-m-deep vertical test range. The experiments are powered by six homopolar generator (HPG) charged inductive stores, sequentially staged to provide the desired acceleration profile. Prior to testing, computer simulations are run to determine the preferred current profile and predict system performance. During projectile flight, high-speed films, X-rays, muzzle volts, and velocity/acceleration profiles are recorded along with power supply operating parameters. Postshot diagnostics include bore wear analysis and armature and target recovery. Comparisons of predicted and recorded shot performance are also made. On selected tests, an energy balance is performed to determine efficiencies of the various components. A summary of all 90-mm gun shots is presented along the critical data collected from selected tests. >

Design and testing of large-bore, ultra-stiff railguns

As part of an EM (electromagnetic) gun technology demonstration program, a systematic design approach targeted at identifying critical gun design constraints affecting hypervelocity projectile performance has been pursued. Results of the study led to a laboratory-based EM gun design that provides bore straightness and tolerances characteristic of light-gas guns, dynamic bore deformations comparable to those of conventional guns, the ability to change and test rail/sidewall insulator materials quickly, and superior in-bore performance diagnostics. A high-stiffness, easily maintained, precision-bore 9-MJ EM launcher has been designed and fabrication is virtually complete. A half-scale prototype of this hydraulically prestressed EM gun design has been fabricated and successfully tested. The authors discuss the railgun design approach and performance parameters, the analytical and empirical railgun structured simulation techniques used to validate the full scale gun design, and the fabrication status and initial performance test results. >

Plasma-armature railgun launcher simulations

The authors review three popular loss models currently used at CEM-UT (Center for Electromechanics at the University of Texas at Austin) in modeling EM (electromagnetic) launchers: friction, ablation, and armature drag. In experiments at currents below 500 kA using existing railgun design, the friction model alone was acceptable in predicting performance. In an experiment incorporating a railgun structure modified for higher stiffness and a measured peak railgun current of 700 kA, the effects of each of the loss models were compared to the measured results, and the greatest success at predicting the final projectile velocity and exit time occurred using the velocity-dependent friction model. It is believed that reducing frictional losses and plasma leakage will be instrumental in achieving velocities greater than 6 km/s. >

9 MJ laboratory gun and range at The University of Texas at Austin

The authors describe a 9 MJ laboratory gun and range program. The goal of the program is to demonstrate a single-shot EM (electromagnetic) gun suitable for establishing gun parameters for repetitive EM gun systems and for supporting projectile development. A description is given of the activities of phase I of this program, wherein the power supply has been prepared, the range has been designed and constructed, a one-half-scale and a full-scale gun have been designed and constructed, and the one-half-scale gun has been assembled and undergone initial tests. Of significance is that within a six-shot test sequence on the one-half-scale gun the electric gun has matched the muzzle velocity of the conventional gun that is operated on the M1E1 battle tank. >

Wear of conductors in railguns: metallurgical aspects

The wear debris generated by an aluminum alloy armature sliding on copper rails was studied experimentally. The experimental parameters were set to maximize armature velocity. Preliminary rail and armature wear observations were documented as part of a database for solid armature development. A variety of debris collection and characterization approaches were used. Both in-bore debris and muzzle-exit debris were collected for size and chemical analysis. Debris constituents were copper-rich, and the compound Cu/sub 9/Al/sub 4/ was observed in the splat-quenched muzzle debris. The approach and method are detailed to indicate the potential of wear studies in defining the activity at the sliding interface. Some implications of rail surface roughening for zero wear measurements are also discussed, and the adoption of wear mechanism maps is proposed. >

Design, analysis, and fabrication of two lightweight, high L' railguns

Design, analysis, and fabrication of two railguns with 90 and 30 mm bores utilizing a laminated containment structure are discussed. Laminations are insulated from each other by layers of sheet adhesive, and a composite overwrap is applied to the laminations for longitudinal stiffness. The 90 mm-bore gun is being fabricated for testing as the 9 MJ range gun. Performance specifications for the 90 mm-bore gun are 3.2 MA peak current, 4.0 km/s maximum velocity, and 12 MJ muzzle energy. The 30 mm-bore gun is a one-third scale version of the 90 mm-bore gun, built to develop construction techniques and verify performance. It is designed to be operated at 1 MA with a maximum muzzle energy of 400 kJ. >

Plasma armature railgun launcher simulations at the University of Texas at Austin

A velocity-dependent friction model that accurately predicts the losses associated with a plasma armature railgun is presented. Test results from a 1-m-long, 1.27-cm square-bore, plasma-armature railgun have been used to determine the validity of the model. The divergence between the calculated and measured performance is typically less than 5% at railgun currents below 500 kA; however, at currents greater than 500 kA, the deviation increases. Experimental evidence suggests that the railguns lack of stiffness and subsequent venting of driving pressure rather than the electromechanical model is primarily responsible for the divergence. To test this theory, a rail was built using external preloading rings (Ringfeder) to increase its stiffness. On the first test of the Ringfeder railgun, 625 kA was discharged into the gun and the projectile was accelerated to 5.9 km/s. Test data indicate that the projectile accelerated through the entire length of the railgun and that a minimum amount of plasma leakage occurred during the test. >

Electromagnetic and structural analyses of an integrated launch package

In this paper, detailed three-dimensional (3D) transient electromagnetic (EM) analyses with temperature-dependent material properties were performed using a state-of-the-art analysis tool to calculate current densities, body force densities, and temperature distribution in launch package and rail conductors. The body force densities, temperature distribution, and package accelerations generated by the EM model were then provided to a 3D multiple-step nonlinear static structural model for detailed mechanical analyses. The combined 3D EM and structural analyses can be used to accurately predict the EM launching performance and launch package structural integrity. Furthermore, armature optimization and package survivability enhancement can also be achieved with the help of these analyses.

Design and development of extremely high velocity electromagnetic launch accelerators-GEDI program

Research is described that has centered around 1, 2, or 8 m long, 12.7 mm square-bore railguns powered by one or more of the following power supplies: a 1 MJ capacitor-bank-driven, pulse-forming network; a 6 MJ homopolar-generator (HPG)-charged coaxial inductor; or one or more of six 10 MJ Balcones-HPG-charged coaxial inductors. Several variations of the 1 and 2 m-long railguns were designed, fabricated, and tested. Railgun design parameters, development, and some test results are described. Parameters of primary importance in designs include sidewall insulator and rail materials; gun length and outer structure materials; stiffness and strength; ease of assembly and disassembly; and availability of methods for supporting, straightening, and honing the guns. Both static and dynamic aspects of railgun structural behavior are discussed. >