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Albuquerque, NM, United States

Tandon R.,Sandia National Laboratories | Paliwal B.,Georgia Institute of Technology | Gibson C.,LMATA Government Services LLC
Philosophical Magazine | Year: 2013

Ring crack initiation loads on glass, using spherical Tungsten carbide (WC) and glass (G) indenters, are measured and analysed. Our measurements demonstrate that environmental humidity plays a key role in determining the load to fracture; experiments conducted without controlling this variable cannot be used to obtain material properties. The role of friction is explicitly considered for dissimilar (WC-G) elastic contacts. For this material pair, the stresses at fracture are well described by a boundary lubrication value of friction coefficient. The fracture loads are used in a fracture-mechanics formulation to calculate crack sizes on glass surfaces. The searched-area concept for dissimilar contacts is described, and used to provide crack density values for these surfaces. © 2013 Taylor & Francis Group, LLC. Source


Youchison D.L.,Sandia National Laboratories | Ulrickson M.A.,Sandia National Laboratories | Bullock J.H.,LMATA Government Services LLC
Proceedings - Symposium on Fusion Engineering | Year: 2011

Plasma disruptions and Edge Localized Modes (ELMS) may result in transient heat fluxes as high as 5 MW/m2 on portions of the ITER first wall (FW). To accommodate these heat loads, roughly 50% of the first wall will have Enhanced Heat Flux (EHF) panels equipped with water-cooled hypervapotron heat sinks. © 2011 IEEE. Source


Skogen E.J.,Sandia National Laboratories | Vawter G.A.,Sandia National Laboratories | Tauke-Pedretti A.,Sandia National Laboratories | Peake G.M.,Sandia National Laboratories | And 4 more authors.
2010 23rd Annual Meeting of the IEEE Photonics Society, PHOTINICS 2010 | Year: 2010

We demonstrate an optical gate architecture using electro-absorption modulator/photodiode pairs to perform AND and NOT functions. Optical bandwidth for both gates reach 40 GHz. Also shown are AND gate waveforms at 40 Gbps. ©2010 IEEE. Source


Youchison D.L.,Sandia National Laboratories | Ulrickson M.A.,Sandia National Laboratories | Bullock J.H.,LMATA Government Services LLC
IEEE Transactions on Plasma Science | Year: 2012

Plasma disruptions and edge localized modes can result in transient heat fluxes as high as 5 MW/m 2 on portions of a tokamak reactor first wall (FW). To accommodate these heat loads, the FW will likely use water-cooled hypervapotron heatsinks to enhance the heat transfer. In this article, we present the results of a computational fluid dynamics (CFD) study using 70 °C inlet water at 2.7 MPa to investigate the tooth height and backchannel depth of 50-mm-wide hypervapotrons with 6-mm-pitch and 3-mm side slots. We compare a popular design with 4-mm-high teeth and a 5-mm backchannel to a more optimal case with 2-mm-high teeth and a 3-mm backchannel under nominal heat loads (0.5 MW/m 2) on a 100-mm-heated length and under single-phase flow conditions. Better heat transfer in the latter case and the smaller backchannel permit a factor of two reduction in the required mass flow while maintaining the same beryllium armor surface temperatures near 130°C. The shallow teeth and smaller backchannel allow the 40 fingers in a typical panel to flow in parallel and simplify the water circuit. A comparison of the two hypervapotron designs during off-normal loading (5.0 MW/m 2) and two-phase flow then follows. The design with 2-mm teeth has a 3.5% higher beryllium surface temperature of 648°C and reduces the critical heat flux (CHF) by ∼2%. Hypervapotron width also plays a role in heat transfer and CHF. CFD results for 36 and 70 mm wide hypervapotrons compared to the 50-mm case reveal similar thermal performance at low heat flux, but a reduction in CHF with increasing width. This study highlights the necessary compromise between design margin during transient events, effective heat transfer under nominal conditions, limitations on finger width, and the simplicity needed in the water circuit design. © 2012 IEEE. Source


Bellum J.,Sandia National Laboratories | Bellum J.,Sandia Staffing Alliance LLC | Kletecka D.,Sandia National Laboratories | Kletecka D.,LMATA Government Services LLC | And 7 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

Sandia's Large Optics Coating Operation has extensive results of laser induced damage threshold (LIDT) testing of its anti-reflection (AR) and high reflection coatings on substrates pitch polished using ceria and washed in a process that includes an alumina wash step. The purpose of the alumina wash step is to remove residual polishing compound to minimize its role in laser damage. These LIDT tests are for multi longitudinal mode, ns class pulses at 1064 nm and 532 nm (NIF-MEL protocol) and mode locked, sub-ps class pulses at 1054 nm (Sandia measurements), and show reasonably high and adequate laser damage resistance for coatings in the beam trains of Sandia's Z-Backlighter terawatt and petawatt lasers. An AR coating in addition to coatings of our previous reports confirms this with LIDTs of 33.0 J/cm2 for 3.5 ns pulses and 1.8 J/cm2 for 350 fs pulses. In this paper, we investigate both ceria and zirconia in doublesided polishing (common for large flat Z-Backlighter laser optics) as they affect LIDTs of an AR coating on fused silica substrates washed with or without the alumina wash step. For these AR coated, double-sided polished surfaces, ceria polishing in general affords better resistance to laser damage than zirconia polishing and laser damage is less likely with the alumina wash step than without it. This is supported by specific results of laser damage tests with 3.5 ns, multi longitudinal mode, single shot pulses at 1064 nm and 532 nm, with 7.0 ns, single and multi longitudinal mode, single and multi shot pulses at 532 nm, and with 350 fs, mode-locked, single shot pulses at 1054 nm. © 2010 Copyright SPIE - The International Society for Optical Engineering. Source

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