Cygnus Diverter Switch Analysis

The Cygnus Dual Beam Radiographic Facility consists of two 2.25-MV 60-kA 50-ns X-ray sources fielded in an underground laboratory at the Nevada Test Site. The tests performed in this laboratory involve the study of the dynamic properties of plutonium and are called subcritical experiments. From end to end, the Cygnus machines utilize the following components: Marx generator, water-filled pulse-forming line (PFL), water-filled coaxial transmission line, three-cell induction voltage adder (IVA), and rod-pinch diode. The upstream transmission line interface to the PFL is via a radial insulator with coaxial geometry. The downstream transmission line terminates in a manifold where the center conductor splits into three lines which individually connect to each of the IVA cell inputs. There is an impedance mismatch at this juncture. It is a concern that a reflected pulse, due to anomalous behavior in the IVA or diode, might initiate breakdown upon arrival at the upstream PFL/transmission line insulator. Therefore, near the beginning of the transmission line, a radial diverter switch is installed to protect the insulator from overvoltage and breakdown. The diverter has adjustable gap spacing and an in-line aqueous-solution (sodium thiosulfate) resistor array for energy dissipation. There are capacitive voltage probes at both ends of the transmission line and on the diverter switch. These voltage signals will be analyzed to determine diverter performance.