Publications

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The Cygnus Dual Beam Radiographic Facility consists of two identical radiographic sources each with a dose rating of 4-rad at 1 m, and a 1-mm diameter spot size. The development of the rod pinch diode was responsible for the ability to meet these criteria1. The rod pinch diode in a Cygnus machine uses a 0.75-mm diameter, tapered tip, tungsten anode rod extended through a 9-mm diameter, aluminum cathode aperture. When properly configured, the electron beam born off the aperture edge can self-insulate and pinch onto the tip of the rod creating an intense, small x-ray source. The Cygnus sources are utilized as the primary diagnostic on Subcritical Experiments that are single-shot, high-value events. The system timing on Cygnus will be evaluated as related to the following system elements: HV trigger generator, Marx, pulse forming line and rod pinch diode. Spare trigger generators will also be included in this evaluation.

The Cygnus Dual Beam Radiographic Facility consists of two identical radiographic sources each with a dose rating of 4-rad at 1 m, and a 1-mm diameter spot size. The development of the rod pinch diode was responsible for the ability to meet these criteria1. The rod pinch diode in a Cygnus machine uses a 0.75-mm diameter, tapered tip, tungsten anode rod extended through a 9-mm diameter, aluminum cathode aperture. When properly configured, the electron beam born off the aperture edge can self-insulate and pinch onto the tip of the rod creating an intense, small x-ray source. The Cygnus sources are utilized as the primary diagnostic on Subcritical Experiments that are single-shot, high-value events. In such an application, there is a necessity for reliability and reproducibility, as well as a precise measurement of these qualities. On Cygnus, the primary diagnostic for reliability and reproducibility is dosimetry. Thermoluinescent2 dosimeters (TLDs) are used for time-integrated dose, and PIN diodes are used for time-resolved dose. Precision dosimetry calibration methods and results will be presented. Cygnus reliability and reproducibility using TLD dosimetry measurements will be given.

National Security Technologies (NSTec) is developing dense plasma focus (DPF) systems for applications requiring intense pulsed neutron sources. Sandia National Laboratories participated in a limited number of experiments with one of those systems. In collaboration with NSTec, Los Alamos National Laboratory, and Lawrence Livermore National Laboratory, we installed additional electrical and X-ray image measurements in parallel with normal operation of the system. Dense plasma focus machines have been studied for decades, but much of the experimental interest has been on neutron and X-ray yield. The primary goal for the present work was to develop and field high-fidelity and traceably-calibrated current and voltage measurements for comparison to digital simulations. The secondary goals were to utilize the current and voltage measurements to add general understanding of vacuum insulator behavior and current sheath dynamics. We also conducted initial scoping studies of soft X-ray diagnostics. We will show the electrical diagnostics and the techniques used to acquire high-fidelity signals in the difficult environment of the 2 MA, 6 μ plasma focus drive pulse. We will show how we measure accreted plasma mass non-invasively, and the sensitivity to background fill density. We will present initial qualitative results from filtered X-ray pinhole images and spectroscopic data from the pinch region.

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The Cygnus Dual Beam Radiographic Facility consists of two identical radiographic sources each with a dose rating of ∼4-rad at 1 m, and a ∼1-mm diameter spot size. The development of the rod pinch diode (RPD) was responsible for the ability to meet these criteria. The RPD in each machine uses a 0.75-mm tungsten diameter tapered anode rod extended through a 9-mm diameter cathode aperture. When properly configured, the electron beam born off the aperture edge can self-insulate and pinch onto the tip of the rod creating an intense, small x-ray source. These sources are utilized in concert with an imaging system on complex experiments, which are single-shot, high-value events. In such an application there is an emphasis on machine performance (reliability and reproducibility). Vacuum quality is a significant determinator for source performance. In this paper we discuss the Cygnus Dual Beam Radiographic Facility, the associated vacuum systems, vacuum monitor calibration and a multi-purpose vacuum chamber. Vacuum system performance, using various enhancements, will be reported. Using the vacuum system enhancements, as well as other machine tweaks, recent source performance has improved. This new level of performance will be presented via dosimetry and electrical measurements.

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