Publications

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Vulcan is a new pulsed power system at Sandia National Laboratories based on fast Marx technology. Vulcan will serve as an intermediate scale demonstration of a fast Marx system and as a testbed for vacuum insulator testing. Vulcan uses multiple parallel fast Marxes, in a layout we call a Fast Marx Array (FMA), and a pulse forming line (PFL) to generate pulses up to 5 MV with effective pulse lengths for vacuum insulator testing that are relevant to larger facilities like Z. Vulcan consists of two parallel 25 stage Marxes with a total stored energy of up to 20 kJ. Vulcan applies up to 5 MV to a vacuum insulator stack load, thereby enabling testing of large area insulator stacks with areas on the order of 1000 cm2. The PFL design includes an oil output switch to adjust the voltage stress duration applied to the vacuum insulator. We will discuss Vulcan's design, including the FMA, Marx trigger generator, energy diverter, PFL, oil output switch, and results of initial commissioning experiments.

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Herein we present details of the design, simulation, and performance of a 100-GW linear transformer driver (LTD) cavity at Sandia National Laboratories. The cavity consists of 20 "bricks." Each brick is comprised of two 80 nF, 100 kV capacitors connected electrically in series with a custom, 200 kV, three-electrode, field-distortion gas switch. The brick capacitors are bipolar charged to ±100 kV for a total switch voltage of 200 kV. Typical brick circuit parameters are 40 nF capacitance (two 80 nF capacitors in series) and 160 nH inductance. The switch electrodes are fabricated from a WCu alloy and are operated with breathable air. Over the course of 6,556 shots the cavity generated a peak electrical current and power of 1.03 MA (±1.8%) and 106 GW (±3.1%). Experimental results are consistent (to within uncertainties) with circuit simulations for normal operation, and expected failure modes including prefire and late-fire events. New features of this development that are reported here in detail include: (1) 100 ns, 1 MA, 100-GW output from a 2.2 m diameter LTD into a 0.1 Ω load, (2) high-impedance solid charging resistors that are optimized for this application, and (3) evaluation of maintenance-free trigger circuits using capacitive coupling and inductive isolation.

A new Wolter x-ray imager has been developed for the Z machine to study the emission of warm (>15 keV) x-ray sources. A Wolter optic has been adapted from observational astronomy and medical imaging, which uses curved x-ray mirrors to form a 2D image of a source with 5 × 5 × 5 mm3 field-of-view and measured 60-300-μm resolution on-axis. The mirrors consist of a multilayer that create a narrow bandpass around the Mo Kα lines at 17.5 keV. We provide an overview of the instrument design and measured imaging performance. In addition, we present the first data from the instrument of a Mo wire array z-pinch on the Z machine, demonstrating improvements in spatial resolution and a 350-4100× increase in the signal over previous pinhole imaging techniques.

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