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Researchers at the Weapons and Materials Research Directorate of ARL have recently completed experimental testing with a G-hardened gun launched miniature instrumentation package that fits within the projectile fuze cavity for obtaining realistic in-bore, deceleration and projectile impact data. This device consists of an accelerometer and a digital recorder that is designed for the reliable capture of ballistic data during projectile launch, flight and target impact. During recent flight test evaluation at the ARL, APG, projectiles containing this device were tested with a telemetry link as well as recovery and direct downloading of on board recorded data. For projectile impact studies both concrete and bunker targets were successfully engaged. This methodology of on board data recording has been shown to provide a reliable and high fidelity characterization of projectile in-bore and impact events critical for advanced munitions designers., Presented at the International Symposium on Electromagnetic Launch Technology (EML) (13th) held in Potsdam, Germany on 22-25 May 2006. The original document contains color images.

Recent experiments with die-level silicon carbide (SiC) transistors are described. The objective of these experiments was to determine the behavior of SiC field effect transistors (FET) in a high-g environment typical of conventional guns, missiles, or electric launchers. The results of the experiments have shown for the first time that die-level SiC FETs can survive mechanical forces as much as 12,000 times the force of gravity (12,000 g's) without the mechanical support and protection of microelectronics encapsulation materials (e.g., plastic encapsulation material or PEM). A second series of experiments was performed with commercial off-the-shelf (COTS) sensors that rely upon standard sensor technology, including silicon (Si) semiconductors. These experiments provided details of several COTS sensors previously qualified for high- G environments, which are characterized here under harsh electromagnetic interference (EMI) conditions. The sensors tested included an Si optical solar cell, an accelerometer, and a magnetometer. The output response of the sensors was recorded during the EMI event to ascertain the effect of coupled electromagnetic radiation on the sensors., Prepared in collaboration with Cornell Univ., Ithaca, NY.

The experiments described demonstrate the electrical behavior of SiC and metal ohmic-contact layers as a function of thermal stress. It has been determined from these experiments that both titanium (Ti) and tantalum (Ta) metalization structures will provide a stable electrical ohmic-contact with n-type SiC after exposure to elevated temperatures for short bursts of time that are considered relevant for pulsed-powered electric weapon technologies. The Ti-SiC structure investigated exhibited a stable current-voltage (I-V) characteristic to as much as 800 deg C for a 10-min burst, while Ta metalizations provided a stable I-V characteristic on SiC even after a temperature burst of 1,000 deg C for as long as a 3-min interval. For samples of n-type, 4H SiC, metalized with (Ti), the standard deviation in resistance (resistivity) of the measured samples is less than 0.17 ohms for a sample having an average resistance of 4.45 ohms. For the Ta contact on SiC, the standard deviation in resistance is 0.05 ohms for a sample having an average resistance of 4.25 ohms. The experiments showed that for both Ti and Ta metalized SiC samples, the change in resistivity of annealed samples is between 3.8% and 1.2% compared to the average values of sample resistance based upon the I-V measurement technique used. These results indicate the ability of Ti-SiC and Ta-SiC structures to perform in a stable manner without significant electrical degradation to the metal contact, SiC substrate, or the metal-semiconductor interface as a function of high-temperature burst conditions.

Successful application of the electrothermal chemical (ETC) propulsion concept will require an understanding of the propagation and interaction of plasmas in propellant beds. This information is necessary to exploit the ignition and combustion control that is possible with plasmas. Toward this end, an experimental program was designed to gain an understanding of the functioning of the plasma and the interaction of the plasma with the propelling charge, and family a series of 30-mm gun tests, incorporating the experience gained in the first two parts of the program, was conducted. This report describes the results of the first two parts of this program. Here results are described of tests on different igniter centercore configurations to be used for distributing the electrical plasma within the combustion chamber. High speed photographic measurements were made of open air firings (with various centercore designs) and in a 30-mm gun simulator. Propagation velocities along with the time sequence of events for the functioning in the centercore tubes were recorded. High axial pressure gradients were observed, necessitating mechanically robust centercores. Radiation levels substantially in excess of conventional igniters were also noted. These observations were exploited in the design of a plasma distribution centercore for 30-mm gun tests.

Recently the development of a PC-based, end to end electrothermal chemical (ETC) gun ballistic simulation code called the pulsed power plasma interior ballistics (PPIB) was completed. PPIB is a time dependent, lumped parameter, electrothermal chemical gun ballistic simulator which has a one dimensional plasma submodel. The PPIB code is used to simulate the three main subsystems of the overall ETC gun system, including the pulse power subsystem, the plasma cartridge, and the interior ballistic process. PPIB is a linkage of three well-established systems models: (1) P2SIM for pulse power, developed by PCRL to model electric gun pulse power supplies, (2) the plasma cartridge code of Powell and Zielinski from the U.S. Army Research Laboratory (ARL), and (3) the latest version of the interior ballistics code IBHVG2 from ARL. PPIB is written in American National Standards Institute (ANSI) standard formula translator (FORTRAN) and is designed to run on any 386, 486 or Pentium-based PC platform. The code has been validated against a 4-MJ pulsed power system, 30-mm ETC plasma experiments, and plasma capillary calculations from the stand alone Powell code, all of which are presented here. In addition, results obtained for high energy plasma simulations are provided. Included in this study are (1) the electrical behavior and transfer efficiencies of various plasma capillary tubes; (2) the amount of energy partitioned to each of the constituents within the plasma such as internal, kinetic, and work energy; and (3) the radiant energy partitioning of the plasma inside the capillary tube during the electrical discharge. The study is concluded with an estimate of the overall energy delivered for the entire process of power supply discharge to electrical plasma generation and radiation for a given test case.

Theoretical calculations are performed with a one dimensional, steady state, isothermal plasma code from the U.S. Army Research Laboratory for the purpose of defining plasma output parameters based on input electrical energies having relevance to the electrothermal chemical (ETC) propulsion concept. Input variables adjusted include capillary diameter, over a range of 1.92 mm to 7.00 mm, and input current amplitude over a range of 30 kA to 350 kA. The capillary length is fixed at 11.84 cm. Plasmas are classified according to their total power and energy level (based on a 3-ms power pulse width) and compared in terms of resistance, exit pressure, and core temperature. Plasma power levels range from 0.17 to 1.89 (GW, while the plasma energy level varies from 0.52 to 5.70 MJ, which is considered adequate coverage for ETC ignition through ETC propulsion enhancement concepts. The study reveals that the range of resistance, pressure, and temperature is 12.8 to 195 momega, 19.8 to 2000 MPa, and 2.9 to 13.5 eV, respectively, for the capillary matrix being investigated. Flow conditions for plasma calculations include choked (no pressure boundary) and unchoked (450 MPa pressure boundary condition). Results from theoretical plasma calculations and interpretations from the perspective of capillary implementation into ETC propulsion concepts are also included.

Experiments have been performed with a 100-kJ Pulse Forming Network (PFN) at the U.S. Army Research Laboratory (ARL) for the purpose of characterizing semiconductor diodes which serve as capacitor.protecting crowbar devices. These devices are viewed as critical electronic power components required for electric gun research that is currently in progress within the U.S. Army and elsewhere. As part of this study, computer techniques were used to refine and develop the understanding of the dynamic, or switching, behavior of PFN diodes. In combination with experimental results, the computer simulations helped to define particular conditions within a given electric gun system that can cause vulnerable or stressful situations for the semiconductor devices under test. It was determined from analyses of the various data collected, that when operated in a PFN under specific loading conditions (simulated here with fixed resistive loads), diodes are subject to transient or high frequency voltage peaks. In some experimental cases at the ARL, the magnitude of the rate of change in voltage (dV/dt) across the devices was such that catastrophic failure was observed. The details of the boundary conditions necessary for device failure are described and several solutions that will circumvent operational problems including device grouping, choice of diode reverse recovery time, and selection of capacitive and inductive circuit parameters are discussed in detail. Background information describing some fundamental physics of semiconductor diodes and their role in electrothermal-chemical (ETC) propulsion technology is provided first. jg