Mechanical Engineering - Story Archives: Advances in Alternate Energy, Professor Wins 2 Million Supercomputer Hours to Study Nuclear Fusion

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Advances in Alternate Energy:
    Professor Wins 2 Million Supercomputer Hours
    to Study Nuclear Fusion

    (Assistant Professor Chuang Ren, Mechanical Engineering
    and Physics; Scientist, Laboratory for Laser Energetics)

     by Lois H. Gresh

February 1, 2007: Assistant Professor Chuang Ren of the University of Rochester Mechanical Engineering Department has won a Department of Energy (DOE) award of 2 million supercomputer hours to do detailed computational analyses for nuclear fusion research. Many experts believe that nuclear fusion, which is the energy of the sun and stars, is the key to global energy needs. Dr. Ren, who is also a Scientist at the University's Laboratory for Laser Energetics (LLE), received one of only 45 DOE "Innovative and Novel Computational Impact on Theory and Experiment (INCITE)" awards granted to researchers for 2007.

Between now and January 8, 2008, Ren will use his 2 million processor hours on the NERSC high-performance computer at Lawrence Berkeley National Laboratory in California, where he will perform detailed simulations of fast ignition, a new idea in support of inertial confinement fusion research using the LLE's 60-beam 30-kilojoule OMEGA laser system and the new high-intensity, short-pulse system OMEGA-EP currently under construction.

The University of Rochester LLE is the world's leading academic institution in the field of fusion energy research with high-power laser beams.

Image -- View of the inside of the multiterawatt facility's target chamber

To create, control, and confine high-temperature high-density plasma on Earth rather than in outer space, the LLE uses inertial confinement fusion and laser beams. The 60-beam OMEGA laser and the new OMEGA-EP short-pulse laser at the LLE provide unique opportunities to compress and heat pellets of materials (such as deuterium and tritium) and create high-temperature high-density plasma.

Fast ignition is a two-step process. First, long pulses, such as those from the 60-beam OMEGA, are aimed at a pellet from all sides and compress the pellet to incredible densities of hundreds of millions of atmospheres. Next, a short pulse, such as that from the OMEGA-EP, generates a beam of energetic electrons that penetrates the very dense region of the compressed pellet and deposits energy in the dense core. The deposited energy produces a hot spot of well over 100 million degrees Centigrade, thus igniting the fuel and kicking off the fusion process.

Dr. Ren's research in theoretical and computational plasmas makes extensive use of supercomputers to simulate and model interactions between lasers and plasma. His simulation of the fast ignition process shows that the detailed geometry of the laser-plasma interface can have profound effects on energetic electrons' generation and their flow. The electrons could end up at wide angles instead of coalescing into a single filament needed to produce ignition. Ren's research provides insight on how to optimize this fast ignition process.

In addition to inertial confinement fusion, Ren's work in theoretical plasmas covers a wide range of applications, including plasmas in astrophysics, plasma-based accelerators, and new radiation sources.  This research is also part of the High-Energy Density Physics research at the Laboratory of Laser Energetics.

Image -- Plasma electron density profile
from a simulation of a fast ignition of a deuterium pellet

Braided Laser Beams

Another example of Ren's research is a study of how two laser beams that pass through a plasma at the same time can influence each other. Although two laser beams do not attract or repel each other in a vacuum (or without a plasma), there can be effective attractive and repulsive forces between two laser beams when both traverse a plasma. The attractive force between the two lasers can cause them to spiral around each other and form a braided pattern. This work is useful in understanding the interactions between the individual laser beams that are used to compress fuel targets for inertial confinement fusion.

Yet another of example of Ren's research is that laser pulses can be deflected by a strong magnetic field applied to a plasma. This may lead to a new way of steering and bending very intense laser pulses.

Image -- Simulation of the electric field of two laser beams interacting with each other inside a plasma

Additional Details

For further details, see:

"A global simulation for laser driven MeV electrons in 50 micron-diameter fast ignition targets," Physics of Plasmas, Vol. 13, Issue 5, p.056308 (May 2006); available at the Los Alamos Preprint Server at http://arxiv.org/abs/physics/0601200; and "A global simulation for laser driven MeV electrons in fast ignition," Phys. Rev. Lett. 93, 185004 (2004).

"Nonlinear and three dimensional theory for cross-magnetic field propagation of short-pulse lasers in underdense plasmas," Phys. Plasmas 11, 1978 (2004);  "On the mutual interaction between laser beams in plasmas," Physics of Plasmas 9, 2354 (2002); and "Mutual attraction of laser beams in plasmas: braided light," Phys. Rev. Lett. 85, 2124 (2000).

For more information, please contact:
   Assistant Professor Chuang Ren
   Email: cren@lle.rochester.edu
   Faculty Webpage: http://www.me.rochester.edu/People/Faculty/ren.html and
http://spider.pas.rochester.edu/mainFrame/people/pages_old/Ren.html

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