Scientists have high hopes for fusion simulation

By Merry MayerSpecial to GCNThe Energy Department wants to push commercial software companies to develop supersoftware, just as it has pushed hardware developers and manufacturers to develop supercomputers.Scientists at Energy's Lawrence Livermore National Laboratory in Livermore, Calif., are hoping for improved visualization software that could provide detailed imaging of fusion reactions that occur in just three-billionths of a second.Until the private sector catches up with its special needs, however, Energy must support its own software, MeshTV. It allows visualization and analysis of data using 2-D and 3-D images. It also provides different ways of viewing the data, including both orthogonal and arbitrary slicing, and is virtually hardware and vendor independent, said Terri Quinn, assistant head of the Scientific Computing and Communications Department at Lawrence Livermore.The lab's National Ignition Facility is using the homegrown software for experiments in which scientists simulate fusion reactions on a small scale to test their instabilities.For physicists, instability is the degree of mixing of elements, which, depending on the circumstances, can be a good or bad thing. The more elements mix, the higher the instability.Lack of instability is why smog hangs over much of Los Angeles, said Andrew Cook, an NIF physicist. There isn't enough mixing of the air, so the air gets trapped in the valley.Instability is also a good thing when it comes to jet engines, which need lots of mixing of air for combustion and takeoff, Cook said.But instability is not good when it comes to nuclear weapons, he said. Mixing of elements can cause the capsules' shells to break up and prevent ignition.Scientists replicate the fusion environment in the lab by shooting a powerful laser at a fusion capsule the size of a BB, causing it to implode and create a tiny star.Such simulations could someday let Energy determine whether a nuclear weapon works without testing it. The simulations also could give astrophysicists new insight into the formation of stars and possibly provide a new source of energy, officials said.But to get a computerized visual of a complex reaction occurring in just three-billionths of a second would require software capable of processing millions of data elements quickly.Energy's Accelerated Strategic Computing Initiative has five large contracts with universities to develop some aspect of visualization computing, said Derrol Hammer, high-performance computing procurement group leader at Lawrence Livermore.The institutions are Stanford University, California Institute of Technology, University of Chicago, University of Illinois at Urbana-Champaign and University of Utah.ASCI is collaborating with Computational Engineering International of Morrisville, N.C., to make its Ensight graphics software scalable for the lab's purposes, Quinn said.Ensight software lets scientists slice the action into planes and actually see what is going on in different sections of the capsule as it implodes, she said. Scientists can also do a particle trace, following it through the capsule as the action occurs.'Unfortunately, it isn't scalable for our purposes at this time,' Quinn said.Late last year, Lawrence Livermore successfully completed the first 3-D simulation of a nuclear weapon primary explosion using its ASCI Blue Pacific supercomputer, one of the most powerful computers in the world, and MeshTV software.Nuclear weapons consist of two main components: the primary or trigger and the secondary, which produces most of the energy.To simulate a primary explosion on a computer required 300G of RAM and some 20 days to complete the calculation. DOE estimated that such a calculation on a regular desktop computer would have taken 30 years to complete.The Blue Pacific is a greatly expanded version of IBM's RS/6000 SP Scalable PowerParallel supercomputer. The ASCI Blue Pacific has 5,856 processors, 1,464 nodes and takes up 8,000 square feet of space. It can perform 3.88 trillion floating-point operations per second and has 75T of space, enough to store the contents of all the books in the Library of Congress.Scientists analyze the visualizations on workstations from SGI. The workstations are connected to the lab's supercomputer by a high-speed HIPPI/OC-12 network. The servers employ switched video and remote rendering to the analysts' workstations, providing multiple levels of graphics capabilities, officials said.Although the main goal of NIF is to ensure the safety and reliability of the nation's nuclear weapons, Energy is also looking beyond this to possible contributions to basic science and its commercial applications.If NIF can achieve fusion ignition and a net engery gain, it will have demonstrated that fusion reactions can be controlled and used as an energy source. Nuclear fusion is much cleaner, with no hazardous byproducts as with nuclear fission, and there is an unlimited supply of fuel, Cook said.Such simulations should also give insight into how stars behave under various circumstances, he said.