VISAR Validation Test Series at the Light Initiated High Explosive (LIHE) facility.

Abstract

A velocity interferometer system for any reflector (VISAR) was recently deployed at the light initiated high explosive facility (LIHE) to measure the velocity of an explosively accelerated flyer plate. The velocity data from the flyer plate experiments, using the vendor's fringe constant of 100m/s/fringe, were consistently lower than model predictions. The goal of the VISAR validation test series was to confirm the VISAR system fringe constant. A low velocity gas gun was utilized to impact and accelerate a target at the LIHE facility. VISAR velocity data from the accelerated target was compared against an independent velocity measurement. The data from this test series did in fact reveal the fringe constant was significantly higher than the vendor's specification. The correct fringe constant for the LIHE VISAR system has been determined to be 123 m/s/fringe. The Light Initiated High Explosive (LIHE) facility recently completed a Phase I test series to develop an explosively accelerated flyer plate (X-Flyer). The X-Flyer impulse technique consists of first spraying a thin layer of silver acetylide silver nitrate explosive onto a thin flyer plate. The explosive is then initiated using an intense flash of light. The explosive detonation accelerates the flyer across a small air gap towards the test item. The impact of the flyer with the test item creates a shock pulse and an impulsive load in the test unit. The goal of Phase I of the X-Flyer development series was to validate the technique theory and design process. One of the key parameters that control the shock pulse and impulsive load is the velocity of the flyer at impact. To measure this key parameter, a velocity interferometer system for any reflector (VISAR) was deployed at the LIHE facility. The VISAR system was assembled by Sandia personnel from the Explosive Projects and Diagnostics department. The VISAR was a three leg, push-pull system using a fixed delay cavity. The primary optical components consisted of a delay bar and stand off that holds the air-reference mirror. When this component was ordered 2 years ago, a fringe constant of 100 m/s/fringe for a 532nm laser was specified. The fabrication/assembly vendor went out of business shortly after delivering the component and did not deliver the certification papers with the component. The vendor documentation to verify the fringe constant was not made available to Sandia. VISAR systems were generally not calibrated because the fringe constant could be determined from a known glass index of refraction and length. The VISAR system was deployed at the LIHE facility using the specified 100m/s/fringe. The Phase I X-Flyer development series was completed successfully measuring flyer velocities using the VISAR system. However flyer velocity measurements were on average 18% lower than analytical model predictions. In an effort to resolve the consistently slow velocity data, the VISAR data was under scrutiny. The purpose of the LIHE VISAR validation test series is to verify the velocity data taken with the VISAR system.