Cygnus Performance in Subcritical Experiments

Summary form only given. The Cygnus Dial Beam Radiographic Facility consists of two identical radiographic sources with the following specifications: 4-rad dose at 1 m, 1-mm spot size, 50-ns pulse length, 2.25-MeV endpoint energy. The facility is located in an underground tunnel complex at the Nevada Test Site. Here subcritical experiments are performed to study the dynamic properties of plutonium. The Cygnus sources were developed as a primary diagnostic for these tests. Since subcritical tests are single-shot, high-value events -reliability and reproducibility are key issues. Enhanced reliability involves minimization of failure modes through design, inspection, and testing. Many unique hardware and operational features were incorporated into Cygnus to insure reliability. Enhanced reproducibility involves normalization of shot-to-shot output also through design, inspection and testing. The first SCE to utilize Cygnus, Armando, was executed on May 25, 2004. A year later, April -May 2005, calibrations using a plutonium step wedge were performed. The results from this series were used for more precise interpretation of the Armando data. In the period January -April 2007 Cygnus is fielded on Thermos, which is a series of several small-sample plutonium shots using a one-dimensional geometry. Pulsed power research generally dictates frequent change in hardware configuration. Conversely, subcritical applications have typically required constant machine settings. Therefore, while operating during the past three years we have accumulated a large database for evaluation of machine performance under highly consistent operating conditions. Through analysis of this database the reliability and reproducibility on Armando, Step Wedge, and Thermos will be presented.