Fabry-Perot Velocimeter Research Articles

Shock loading characteristics of Zr and Ti metals using dual beam velocimeter

The characteristics of titanium and zirconium metal foils under shock loading have been studied up to 16 GPa and 12 GPa pressure, respectively, using portable electric gun setup as projectile launcher. In these experiments, the capabilities of a single Fabry-Perot velocimeter have been enhanced by implementing it in dual beam mode to record the two velocity profiles on a single streak camera. The measured equation of state data for both the metals have been found to be well in agreement with the reported Hugoniot, within experimental accuracies. A phase transition from α to ω phase has been detected near to 11.4 GPa for titanium and 8.2 GPa for zirconium in the rising part of target-glass interface velocity profile.

Measuring the Free Surface Velocity of Brass Plate Using F-P Interferometer

Brass plates with a diameter of 100 mm and thickness of 2.0 mm or 0.87 mm were accelerated by TNT and Comp. B charges. A plane wave generator with 100mm in diameter was used to form one-dimensional detonation within the charge. Six acceleration jumps of the plate free surface caused by the interactions between the incident and reflective waves were observed by use of a Fabry-Perot velocimeter and an image converter camera system. We believe that the experimental system adopted in present work provides a perfect technique for studying the detonation properties of the explosives and the dynamic response of materials to the impulsive loading.

Equation of state measurements using single Fabry-Perot velocimeter

Accurate measurement of projectile and free surface velocity of target is a crucial part of any high pressure physics experiments involving hyper velocity impact. Fabry Perot velocimeter (FPV) is a widely accepted technique for single surface velocity measurements. In the present work a possibility of using single FPV for two surface velocity measurements is experimentally explored. The laser light is launched in such a way that it illuminates both the surfaces under study and reflected light coming from the flyer as well as from the target is used to generate interference fringes. Therefore by recording fringe displacements due to Doppler shift in reflected light corresponding to movement of both the surfaces at different time instants, velocity profile of both target and projectile can be computed. This technique has been utilized for equation of state measurements of polyurethane based retro-reflective tape at 12 GPa and aluminum at 15 GPa. Measured peak particle velocities at the target-glass interface have been found in good agreement with the reported equation of state data.

Shock experiments and numerical simulations on low energy portable electrically exploding foil accelerators

Two low energy (1.6 and 8 kJ) portable electrically exploding foil accelerators are developed for moderately high pressure shock studies at small laboratory scale. Projectile velocities up to 4.0 km/s have been measured on Kapton flyers of thickness 125 microm and diameter 8 mm, using an in-house developed Fabry-Perot velocimeter. An asymmetric tilt of typically few milliradians has been measured in flyers using fiber optic technique. High pressure impact experiments have been carried out on tantalum, and aluminum targets up to pressures of 27 and 18 GPa, respectively. Peak particle velocities at the target-glass interface as measured by Fabry-Perot velocimeter have been found in good agreement with the reported equation of state data. A one-dimensional hydrodynamic code based on realistic models of equation of state and electrical resistivity has been developed to numerically simulate the flyer velocity profiles. The developed numerical scheme is validated against experimental and simulation data reported in literature on such systems. Numerically computed flyer velocity profiles and final flyer velocities have been found in close agreement with the previously reported experimental results with a significant improvement over reported magnetohydrodynamic simulations. Numerical modeling of low energy systems reported here predicts flyer velocity profiles higher than experimental values, indicating possibility of further improvement to achieve higher shock pressures.

High-precision velocimetry: optimization of a Fabry–Perot interferometer

We present the optimization of a Fabry-Perot velocimeter designed to measure speed at a few millimeters per second with a relative uncertainty of 10(-8). We focus on the accuracy and the optimization of the Fabry-Perot, with a review of the uncertainties related to the geometry, the beam shape, and the Doppler frequency measurement. These errors are quantified to ensure that the required accuracy is reached. We then describe the practical implementation and show the results.

Time-resolved diagnostics for concrete target response

In order to facilitate the design of advanced penetrating weapons for defeating land targets, the interaction of concrete with high-velocity penetrators needs to be better characterized. To aid in this effort, three new types of time-resolved diagnostics are being developed and have been used in two experiments and one demonstration: fiber optic arrays to localize penetrators in space and time, Fabry-Perot velocimetry to record the concrete particle velocity, which is related to the pressure, at specific locations within concrete targets, and micropower impulse radar to provide a non-intrusive measure of the penetrator position-time history in a target. The two experiments used the fiber optic array and the Fabry-Perot velocimeter to diagnose the response of concrete to penetration by a Viper shaped charge jet. The results were analyzed using the CALE continuum mechanics simulation program, for which a preliminary model of the material properties of concrete was developed. The fiber optic arrays recorded the bow shock at locations 6.4 and 16.9 cm from the front surfaces. The Fabry-Perot velocimeter measured a free-surface velocity of 0.13 km/s at a distance of 3 cm and obliquity 70° from the jet, which was moving at an interface velocity of 4.0 km/s at a depth of 29 cm. These values imply a pressure of about 6.6 kbar at that location. The demonstration used micropower impulse radar with a pulse repetition frequency of 0.25 MHz and a cell size of 30 ps to detect and record the motion of a metal penetrator simulant moving inside a cylindrical concrete target.

Formulas for Fabry–Perot velocimeter performance using both stripe and multifrequency techniques

New stripe and multifrequency techniques for Fabry-Perot velocimetry are incorporated into an analytical model for the entire system. Properties of striped interferometers (FP's) are derived. An understanding of energy flow in both striped and unstriped FP's is presented. Nine contributions to the velocity resolution are examined, and analytical approximations are provided for each of them. Formulas for the overall velocity and time resolution of each fringe are derived. Using brightness arguments to limit the maximum usable light acceptable by the system, we also derived analytical limits on the photographic writing speed of each fringe.

A study of detonation processes in heterogeneous high explosives

A model of multiple processes is used to simulate the behavior of reaction in detonation of heterogeneous high explosives. The features of the model are (1) the partition of the explosive medium into hot spots and the region exclusive of hot spots and (2) the separation of the mechanical-thermal process and chemical process. For each process, a characteristic time is assigned and is defined by a phenomenological relation. With assumptions, some fast processes are ignored in the governing equations. This investigation indicates the necessity of including a slow process near the end of the reaction. Comparisons with experiments using a Fabry–Perot velocimeter are presented for triaminotrinitrobenzene.