Publications

The shape and magnitude of an energetically driven shock wave as it passes through a recipient device or sensor are critical factors that influence the performance and integrity of the device. Here we report on the design and analysis of a coupled energetic train and sensor system using the Sandia-developed strong shock physics code, CTH. We have investigated several strategies for reducing the curvature and manipulating the shape of energetically-driven shock waves to more closely match the ideal profile that the sensor is designed for. Flat flyer plates and wave-shaped disks are promising in certain applications. Experimental validation of the theoretical results is also underway and briefly described here. ©2009 Society for Experimental Mechanics Inc.

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Diversionary devices such as flashbang grenades are used in a wide variety of military and law-enforcement operations. They function to distract and/or incapacitate adversaries in scenarios ranging from hostage rescue to covert strategic paralysis operations. There are a number of disadvantages associated with currently available diversionary devices. Serious injuries and fatalities have resulted from their use both operationally and in training. Because safety is of paramount importance, desired improvements to these devices include protection against inadvertent initiation, the elimination of the production of high-velocity fragments, less damaging decibel output and increased light output. Sandia National Laboratories has developed a next-generation diversionary flash-bang device that will provide the end user with these enhanced safety features.

The velocity of short duration high-amplitude shock waves and high-speed motion created by sources such as explosives, high energy plasmas and other rapid-acceleration devices are difficult to measure due to their fast reaction times. One measurement tool frequently used is VISAR (Velocity Interferometer System for Any Reflector). VISAR is an optical-based system that utilizes Doppler interferometry techniques to measure the complete time-history of the motion of a surface. This technique is gaining worldwide acceptance as the tool of choice for measurement of shock phenomena. However, one limitation of the single point VISAR is that it measures only one point on a surface. The new Multi Point VISAR remedies the single point VISAR's limitation by using multiple fiber optics and sensors to send and receive information. Upcoming programs that need analysis of large diameter flyers prompted the concept and design of a single cavity-multiple fiber optic Multi Point VISAR (MPV). Preliminary designs and the testing of a single cavity prototype in 1996 supported the theory of compact fiber optic bundle systems for development into the Multi Point VISAR. The new MPV was used to evaluate the performance of two components; a piezo-driven plane wave generating isolator, and a slim-loop ferroelectric (SFE)-type fireset.

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The Saturn accelerator at Sandia National Laboratories is a high power, variable-spectrum, x-ray source capable of simulating radiation effects of nuclear countermeasures on electronic and material components of space systems. It can also function as a pulsed-power and radiation source, and as a diagnostic test bed for a variety of applications. Obtaining highly accurate measurements of the emission spectra is difficult because the high intensity x-rays and MegaAmpere levels of current inside the experiment chamber can damage or destroy electronic measurement devices. For these reasons, an optical based measurement system has been designed, developed and successfully tested in the Saturn accelerator. The system uses fiber optic coupled sensor(s) connected to a specialized Doppler interferometer system which analyzes the shock wave imparted into a target material. This paper describes the optical system, its related components, and material response data of polymethyl methacrylate.

VISAR (Velocity Interferometer System for Any Reflector) is a system that uses the Doppler effect and is widely used for measuring the velocity of projectiles, detonations, flying plates, shock pressures (particle velocity) and other high speed/high acceleration motion. Other methods of measurement such as accelerometers and pressure gauges have disadvantages in that they are sensitive to radiation, electromagnetic pulses, and their mass can drastically alter the velocity of the projectile. VISAR uses single frequency-single mode laser fight focused onto a target of interest. Reflected fight from the target is collected and sent through a modified, unequal leg Michelson interferometer. In the interferometer the light is split into two components which travel through the legs of the interferometer cavity and are then recombined. When the light recombines, an interference pattern is created which can range from dark (destructive interference) to bright (constructive interference). When the target moves, the reflected laser light experiences a frequency shift (increase) with respect to the frequency from the target in a static condition. Since the Doppler shifted light is split and routed through an unequal leg interferometer cavity, there is a time lag of the light containing the Doppler information at the recombination point in the interferometer. The effect of the time lag is to create a sinusoidally changing interference pattern (commonly called fringes). Since the interferometer time delay, laser wavelength, and the speed of light are known, an accurate measurement of target velocity/acceleration may be measured by analyzing both the number of tinges and the speed of tinge generation (system accuracy is 3--4%).

Testing and analysis of shock wave characteristics such as produced by detonators and ground shock propagation frequently require a method of measuring velocity and displacement of the surface of interest. One method of measurement is doppler interferometry. The VISAR (Velocity Interferometer System for Any Reflector) uses doppler interferometry and has pined wide acceptance as the preferred tool for shock measurement. An important asset of VISAR is that it measures velocity and displacement non intrusively. The conventional VISAR is not well suited for portability because of its sensitive components, large power and cooling requirements, and hazardous laser beam. A new VISAR using the latest technology in solid state lasers and detectors has been developed and tested. To further enhance this system`s versatility, the unit is fiber optic coupled which allows remote testing, permitting the VISAR to be placed over a kilometer away from the target being measured. Because the laser light is contained in the fiber optic, operation of the system around personnel is far less hazardous. A software package for data reduction has also been developed for use with a personal computer. These new advances have produced a very versatile system with full portability which can be totally powered by batteries or a small generator. This paper describes the solid state VISAR and its peripheral components, fiber optic coupling methods and the fiber optic coupled sensors used for sending and receiving laser radiation.