John Smedley, a physicist in Brookhaven Lab’s Instrumentation DivisionJohn Smedley, master of engineering electron-emitting photocathodes

For twenty years, John Smedley, a physicist in Brookhaven Lab’s Instrumentation Division, has been researching and designing novel accelerator photocathodes—the miniature electron emitters at the heart of accelerator experiments that probe the fundamental laws of nature and the properties of materials for applications in energy technologies and other areas.

When photocathodes are struck by photons—quantum packets of light—they produce electrons, a conversion from light to electric current that has enabled a long history of technological advances. Building these devices requires the delicate manipulation of materials, some composed of layers as thin as a single atom.

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This CASL visualization shows the thermal distribution of neutrons in Watts Bar Unit 1 Cycle 1 reactor core at initial criticality, as calculated by the VERA program.Innovation Hub's reactor simulation model uses utility's data

Scientists at the Consortium for Advanced Simulation of Light Water Reactors have successfully completed the first full-scale simulation of an operating nuclear reactor. CASL, headquartered at DOE's Oak Ridge National Laboratory, is modeling nuclear reactors on supercomputers to help researchers better understand reactor performance with much higher reliability than previously available methods, with the goal of ultimately increasing power output, extending reactor life, and reducing waste.

Simulation results from the Virtual Environment for Reactor Applications (VERA) program, developed by CASL, were compared with actual data provided by the Tennessee Valley Authority's (TVA) Watts Bar Nuclear Plant in Tennessee, which confirmed its accuracy.

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See also…

DOE Pulse
  • Number 393  |
  • July 22, 2013
  • First direct images of topological insulator's edge currents

    This graphic depicts the tiny loop of a scanning SQUID, or superconducting quantum interference device (silver), which detects magnetic fields (red) created by an edge current (blue) in a topological insulator. (Illustration: Greg Stewart) Scientists from DOE's SLAC National Accelerator Laboratory and Stanford University have made the first direct images of electrical currents flowing along the edges of a topological insulator – a recently discovered state of matter with potential applications in information technology.

    In these strange solid-state materials, currents flow only along the edges of a sample while avoiding the interior. Using an exquisitely sensitive detector they built, scientists from the joint SLAC and Stanford Institute for Materials and Energy Sciences (SIMES) were able to sense the weak magnetic fields generated by the edge currents and tell exactly where the currents were flowing.

    "Now no one can doubt that they exist," said Kathryn A. "Kam" Moler, the SIMES and Stanford University physics professor who led the research, which was published June16 in Nature Materials.

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  • Illuminating microbial “dark matter”

    There are more microbes in, on and around the Earth than there are stars in the sky. (Composition by Zosia Rostomian, Berkeley Lab) In cosmology, dark matter is said to account for the majority of mass in the universe. However, the number of microbes in, on and around the planet outnumbers the stars in the sky. Despite their profound influences on the most significant environmental processes, most of these microbes are still unknown. To learn more about these “microbial dark matter,” DOE Joint Genome Institute researchers led an international collaboration to fill in uncharted branches in the bacterial and archaeal tree of life.

    The team sorted 9,000 microbial cells isolated from nine locations around the world, applying single-cell genomics techniques to assemble and identify 201 distinct genomes.

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  • Resistivity switch is window to role of magnetism in iron-based superconductors

    Theoretical predictions made by physicists Jörg Schmalian and Rafael Fernandez (both former Ames Laboratory scientists) along with Naval Research Laboratory’s Igor Mazin and Michelle Johannes, closely matched the experimental findings.Physicists at Ames Laboratory have discovered surprising changes in electrical resistivity in iron-based superconductors. The findings, reported in Nature Communications, offer further evidence that magnetism and superconductivity are closely related in this class of novel superconductors.

     “We found that the directions of smallest and largest resistivity within the conducting layers are significantly dependent on the composition of the compounds, and in some compositions, they change sign, or, in other words, electric current flows easier in the direction that was originally more difficult” said Ames Laboratory faculty scientist Ruslan Prozorov. “This change can only be explained if the underlying magnetic behavior is intimately connected to superconductivity.”

    Understanding the basic physics behind iron-based superconductivity may someday make it possible to use them for super-efficient energy technologies.

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  • Irrigation's impact on clouds and climate

    Crop irrigation is one of the largest ways humans perturb the climate. Including irrigation in model calculations will help bring model estimates closer to a complete representation of the climate. From corn to cotton, irrigation water is needed to grow crops around the world and that same water alters the balance of moisture in soil and the climate, according to scientists at DOE’s Pacific Northwest National Laboratory. Irrigation shifts the balance of water vapor and upward moving air. The impact, seen in dry years especially, is on the layer of air closest to us, which is most susceptible to heat exchange and evaporation from the Earth's surface. In particular, irrigation may play a role in forming shallow clouds, which alter the local climate.

    The PNNL team led the study to incorporate an irrigation representation into the Weather Research and Forecasting  regional climate model. This included adding "sensors" and "triggers" in the model, similar to those used by farmers and others, to detect the need and timing for optimal water use. They evaluated the performance of the improved model in simulating the regional climate and surface water and energy budgets over the Atmospheric Radiation Measurement Southern Great Plains site. The team conducted a series of simulations with and without irrigation over the Great Plains for both an extremely dry year (2006) and wet year (2007).

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