Cygnus Diverter Switch Analysis

Abstract

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 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), waterfilled coaxial transmission line (WTL), 3-cell inductive voltage adder (IVA), and rod-pinch diode. The upstream WTL interface to the PFL is via a radial insulator with coaxial geometry. The downstream WTL 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/WTL insulator. Therefore near the beginning of the WTL a radial diverter switch is installed to protect the insulator from over voltage 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 WTL and on the diverter switch. These voltage signals will be analyzed to determine diverter performance. Using this analysis the usefulness of the diverter switch will be evaluated.

Modeling power flow in the induction cavity with a two dimensional circuit simulation

“…For instance, the output transmission line of the Cygnus machine was conducted as a lossless vacuum transmission line and in positive polarity to drive a rod-pinch diode. The corresponding impedance of the output transmission line at each induction cavity was sufficiently larger than the summed impedance of upstream pulse forming sections in order to avoid electron emission from the negative outer electrode [36,37]. In this situation, not only the output transmission line impedance needs to be carefully chosen to make sure the cathode electric field at a safe level, but also the maximum voltages at the azimuthal transmission line, insulator stack, and radial feed gap sections will be higher than that of the pulse forming section.…”