Publications

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Saturn is a short-pulse ( 40 ns FWHM) x-ray generator capable of delivering up 10 MA into a bremsstrahlung diode to yield up 5 × 10^12 rad/s (Si) per shot at an energy of 1 to 2 MeV. With the machine now over 30 years old it is necessary to rebuild and replace many components, upgrade controls and diagnostics, design for more reliability and reproducibility, and, as possible upgrade the accelerator to produce more current at a low voltage ( 1 MV or lower). Thus it has been necessary to reevaluate machine design parameters. The machine is modeled as a simple LR circuit driven with an equivalent a sine-squared drive waveform as peak voltage, drive impedance, and vacuum inductance are varied. Each variation has implications for vacuum insulator voltage, diode voltage, diode impedance, and radiation output. For purposes of this study, radiation is scaled as the diode current times the diode voltage raised to the 2.7 power. Results of parameter scans are presented and used to develop a design that optimizes radiation output. Results indicate that to maintain the existing short pulse length of the machine but to increase output it is most beneficial to operate at an even higher impedance than originally designed. Also discussed are critical improvements that need to be made.

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A second series of experiments were performed in August 2017 on the Clam Shell Magnetically-Insulated Transmission Line1 (CSMITL2) at the Saturn accelerator at Sandia National Laboratories in Albuquerque. In the first series of experiments in March 2017, the CSMITL2 demonstrated utilizing four vacuum-insulator levels instead of the two in CSMITL1, increasing the load power by a factor of four compared to CSMITL1 delivering 8 TW to the load, and polarity inversion of the power pulse. Obj ectives for the second series included multiple shot per day capability and large ion current densities from a large-area flashover ion diode source.

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This paper describes the software changes made to the data processing and display system for HERMES III accelerator at the Simulation Technology Laboratory (STL) at Sandia National Laboratories, New Mexico. The HERMES III accelerator is a gamma ray simulator producing 100kRad[Si] dose per shot with a full width half max pulse duration of 25 nanoseconds averaging six shots per day. For each accelerator test approximately 400 probe signals are recorded over approximately 65 digitizers. The original data processing system provided the operator a report summarizing the start of probe signal timings for groups of probes located within the power flow conductors. This timing information is indicative of power flow symmetry allowing the operator to make necessary adjustments prior to the next test. The report also provided data overlays concerning laser trigger light output, x-ray diode currents and x-ray source output. Power flow in the HERMES III accelerator is comprised of many circuit paths and detailed current and voltage information within these paths could provide a more thorough understanding of accelerator operation and performance, however this information was either not quickly available to the operators or the display of the data was not optimum. We expanded our data processing abilities to determine the current and voltage amplitudes throughout the power flow conductors and improved the data display abilities so data plots can be presented in a more organized fashion. We detail our efforts creating a software program capable of processing the 400 probe signals together with an organized method for displaying the dozens of current and voltage probes. This process is implemented immediately after all digitizer data has been collected so the operator is provided timing and power flow information shortly after each accelerator shot.

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A new collimated filtered thermoluminescent dosimeter (TLD) array has been developed at the Z facility to characterize warm x-rays (hν > 10 keV) produced by Z pinch radiation sources. This array includes a Kapton debris shield assembly to protect the TLDs from the source debris, a collimator array to limit the field of view of the TLDs to the source region, a filter wheel containing filters of aluminum, copper and tungsten up to 3 mm thick to independently filter each TLD, and a hermetically sealed cassette containing the TLDs as well as tungsten shielding on the sides and back of the array to minimize scattered radiation reaching the TLDs. Experimental results from a krypton gas puff and silver wire array shot are analyzed using two different functional forms of the energy spectrum to demonstrate the ability of this diagnostic to consistently extend the upper end of the x-ray spectrum characterization from ∼50 keV to >1 MeV.

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