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PPPL physicists win supercomputing time to study fusion and the cosmos

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Credit: Elle Starkman/PPPL Office of Communications

More than 210 million core hours on two of the most powerful supercomputers in the nation have been won by two teams led by researchers at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL). The highly competitive awards from the DOE Office of Science's INCITE (Innovative and Novel Impact on Computational Theory and Experiment) program will accelerate the development of nuclear fusion as a clean and abundant source of energy for generating electricity and will advance understanding of the high-energy-density (HED) plasmas found in stars and other astrophysical objects.

A single core hour represents the use of one computer core, or processor, for one hour. A laptop computer with only one processor would take some 24,000 years to run 210 million core hours.

"Extremely important and beneficial"

"These awards are extremely important and beneficial," said Michael Zarnstorff, deputy director for research at PPPL. "They give us access to leadership-class highest-performance computers for highly complex calculations. This is key for advancing our theoretical modeling and understanding." Leadership-class computing systems are high-end computers that are among the most advanced in the world for solving scientific and engineering problems.

The allocations include more than 160 million million core hours for physicist C.S. Chang and his team, marking the first year of a renewable three-year award. The first-year hours are distributed over two machines: 100-million core hours on Titan, the most powerful U.S supercomputer, which can perform some 27 quadrillion (1015) calculations per second at the Oak Ridge Leadership Computing Facility (OLCF); and 61.5 million core hours on Theta, which completes some 10 quadrillion calculations a second at the Argonne Leadership Computing Facility (ALCF). Both sites are DOE Office of Science User Facilities.

Also received are 50 million core hours on Titan for Amitava Bhattacharjee, head of the Theory Department at PPPL, and William Fox and their team to study HED plasmas produced by lasers.

Chang's group consists of colleagues at PPPL and other institutions and will use the time to run the XGC code developed by PPPL and nationwide partners. The team is exploring the dazzlingly complex edge of fusion plasmas with Chang as lead principal investigator of the partnership center for High-fidelity Boundary Plasma Simulation — a program supported by the DOE Office of Science's Scientific Discovery through Advanced Computing (SciDAC). The edge is critical to the performance of plasma that fuels fusion reactions.

Fusion — the fusing of light elements

Fusion is the fusing of light elements that most stars use to generate massive amounts of energy – and that scientists are trying to replicate on Earth for a virtually inexhaustible supply of energy. Plasma – the fourth state of matter that makes up nearly all the visible universe – is the fuel they would use to create fusion reactions.

The XGC code will perform double-duty to investigate developments at the edge of hot, charged fusion plasma. The program will simulate the transition from low- to high-confinement of the edge of fusion plasmas contained inside magnetic fields in doughnut-shaped fusion devices called tokamaks. Also simulated will be the width of the heat load that will strike the divertor, the component of the tokamak that will expel waste heat and particles from future fusion reactors based on magnetic confinement such as ITER, the international tokamak under construction in France to demonstrate the practicality of fusion power.

The simulations will build on knowledge that Chang has achieved in the previous-cycle SciDAC project. "We're just getting started," Chang said. "In the new SciDAC project we need to understand the different types of transition that are thought to occur in the plasma, and the physics behind the width of the heat load, which can damage the divertor in future facilities such as ITER if the load is too narrow and concentrated."

Advancing progress in understanding HED plasmas

The Bhattacharjee-Fox award, the second and final part of a two-year project, will advance progress in the team's understanding of the dynamics of magnetic fields in HED plasmas. "The simulations will be immensely beneficial in designing and understanding the results of experiments carried out at the University of Rochester and the National Ignition Facility at Lawrence Livermore National Laboratory" Bhattacharjee said.

The project explores the magnetic reconnection and shocks that occur in HED plasmas, producing enormous energy in processes such as solar flares, cosmic rays and geomagnetic storms. Magnetic reconnection takes place when the magnetic field lines in plasma converge and break apart, converting magnetic energy into explosive particle energy. Shocks appear when the flows in the plasma exceed the speed of sound, and are a powerful process for accelerating charged particles.

To study the process, the team fires high-power lasers at tiny spots of foil, creating plasma bubbles with magnetic fields that collide to form shocks and come together to create reconnection. "Our group has recently made important progress on the properties of shocks and novel mechanisms of magnetic reconnection in laser-driven HED plasmas," Bhattacharjee said. "This could not be done without INCITE support."

PPPL, on Princeton University's Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. The Laboratory is managed by the University for the U.S. Department of Energy's Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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John Greenwald
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