Publications

Results 11601–11650 of 101,000

Search results

Jump to search filters

Vertical GaN Devices for Medium-Voltage Power Electronics

Kaplar, Robert J.; Allerman, Andrew A.; Crawford, Mary H.; Gunning, Brendan P.; Flicker, Jack D.; Armstrong, Andrew A.; Yates, Luke; Dickerson, Jeramy; Binder, Andrew T.; Abate, Vincent M.; Smith, Michael; Pickrell, Gregory W.; Sharps, Paul; Anderson, T.; Gallagher, J.; Jacobs, A.G.; Koehler, A.; Tadjer, M.; Hobart, K.; Hite, J.; Ebrish, M.; Porter, M.; Zeng, K.; Chowdhury, S.; Ji, D.; Aktas, O.; Cooper, James A.

Abstract not provided.

More Details
TYPE Conference Presentation YEAR 2021
DOIOSTI

Geometric Tail Approximation for Reliability and Survivability

Ackermann, Mark R.; Osborn, Thor D.

A common problem in developing high-reliability systems is estimating the reliability for a population of components that cannot be 100% tested. The radiation survivability of a population of components is often estimated by testing a very small sample to some multiple of the required specification level, known as an overtest. Given a successful test with a sufficient overtest margin, the population of components is assumed to have the required survivability or radiation reliability. However, no mathematical justification for such claims has been crafted without making aggressive assumptions regarding the statistics of the unknown distribution. Here we illustrate a new approach that leverages geometric bounding arguments founded on relatively modest distribution assumptions to produce conservative estimates of component reliability.

More Details
TYPE SAND Report YEAR 2021
DOIOSTI

Applying Incremental, Inductive Model Checking to the Modal Mu Calculus

Rawlings, Blake C.

This work aims to demonstrate that an incremental inductive model checking algorithm built on top of Boolean satisfiability (SAT) solvers can be extended to support modal mu calculus (MMC) formulas. The resulting algorithm, called modal mu calculus model checking using myopic constraints (MC3), solves MMC model checking problems over Boolean labeled transition systems (LTSs). MMC subsumes simple invariance/reachability (as solved by the IC3 algorithm), linear temporal logic (LTL, as solved by the fair algorithm), computation tree logic (CTL, as solved by IICTL), and CTL* (which in turn subsumes LTL and CTL, but was not previously supported by any incremental inductive algorithm). The algorithm is implemented in a prototype solver, mc3.

More Details
TYPE SAND Report YEAR 2021
DOIOSTI

Assessment of Electrode Contamination Mitigation at 0.5 MA Scale

Lamppa, Derek C.; Simpson, Sean; Hutsel, Brian T.; Cuneo, Michael E.; Laity, George R.; Rose, David V.

The Z Machine at Sandia National Laboratories uses current pulses with peaks up to 27 MA to drive target implosions and generate high energy density conditions of interest for stockpile stewardship programs pertinent to the NNSA program portfolio . Physical processes in the region near the Z Machine target create electrode plasmas which seed parasitic current loss that reduce the performance and output of a Z experiment. Electrode surface contaminants (hydrogen, water, hydrocarbons) are thought to be the primary constituent of electrode plasmas which contribute to loss mechanisms. The Sandia team explore d in situ heating and plasma discharge techniques by integrating requisite infrastructure into Sandia's Mykonos LTD accelerator, addressing potential impacts to accelerator operation, and reporting on the impact of these techniques on electrode plasma formation and shot performance. The in situ discharge cleaning utilizes the electrodes of the accelerator to excite an argon-oxygen plasma to sputter and chemically react contaminants from electrode surfaces. Insulating breaks are required to isolate the plasma in electrode regions where loss processes are most likely to occur. The shots on Mykonos validate that these breaks do not perturb experiment performance, reducing the uncertainty on the largest unknown about the in situ cleaning system. Preliminary observations with electrical and optical diagnostics suggest that electrode plasma formation is delayed, and overall inventory has been substantively reduced. In situ heating embeds cartridge heaters into accelerator electrodes and employs a thermal bakeout to rapidly desorb contaminants from electrode surfaces. For the first time, additively manufactured (AM) electrode assemblies were used on a low impedance accelerator to integrate cooling channels and manage thermal gradients. Challenges with poor supplier fabrication to specifications, load alignment, thermal expansion and hardware movement and warpage appears to have introduced large variability in observed loss, though, preventing strong assertions of loss reduction via in situ heating. At this time, an in situ discharge cleaning process offers the lowest risk path to reduce electrode contaminant inventories on Z, though we recommend continuing to develop both approaches. Additional engineering and testing are required to improve the implementation of both systems. .

More Details
TYPE SAND Report YEAR 2021
DOIOSTI

Topology Optimization with a Manufacturability Objective

Robbins, Joshua

Part distortion and residual stress are critical factors for metal additive manufacturing (AM) because they can lead to high failure rates during both manufacturing and service. We present a topology optimization approach that incorporates a fast AM process simulation at each design iteration to provide predictions of manufacturing outcomes (i.e., residual stress, distortion, residual elastic energy) that can be optimized or constrained. The details of the approach and implementation are discussed, and an example design is presented that illustrates the efficacy of the method.

More Details
TYPE SAND Report YEAR 2021
DOIOSTI

Saturn Radiation Dose Environment Characterization

Ulmen, Ben; Depriest, Kendall R.; Olson, Aaron; Webb, Timothy J.; Edwards, Jarrod D.

To understand the environment where a time-resolved hard x-ray spectrometer (AXIOM) might be fielded, experiments and simulations were performed to analyze the radiation dose environment underneath the Saturn vacuum dome. Knowledge of this environment is critical to the design and placement of the spectrometer. Experiments demonstrated that the machine performance, at least in terms of on-axis dose, has not significantly changed over the decades. Simulations of the off-axis dose were performed to identify possible spectrometer locations of interest. The effects from the source and dome hardware as well as source distributions and angles of incidence on the radiation environment were also investigated. Finally, a unified radiation transport model was developed for two widely used radiation transport codes to investigate the off-axis dose profiles and the time-dependent x-ray energy spectrum. The demonstrated equivalence of the unified radiation transport model between the radiation transport codes allows the team to tie future time-dependent x-ray environment calculations to previous integral simulations for the Saturn facility.

More Details
TYPE SAND Report YEAR 2021
DOIOSTI
Results 11601–11650 of 101,000
Results 11601–11650 of 101,000
Top