General Atomics researchers using a Cray X1E supercomputer say they have made a significant breakthrough in their ability to predict what happens inside an experimental fusion reactor, a milestone on the way to developing a stable and efficient new power source. Fusion is the nuclear reaction that fuels stars like the sun and has the potential to produce clean, almost limitless power here on Earth.
The General Atomics scientists are employing a computer code they wrote called GYRO, scaled to the massive compute capabilities of a Cray X1E system located at Oak Ridge National Laboratory (ORNL), to simulate the complex behavior of the super-heated gaseous fuel called plasma as it roils within a reactor. Working under a grant of computer time from the Department of Energy's (DOE's) Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program, the researchers have for the first time been able to simulate both electron and ion plasma turbulence, a crucial step for eventually designing and building a full-scale, energy-producing fusion reactor.
"Approximation is the name of the game in physics," said Jeff Candy, principal scientist in the Energy Group at General Atomics. "GYRO performs a faithful gyrokinetic approximation of the fundamental physics that occurs when the nuclei of deuterium and tritium atoms fuse within a reactor's magnetic containment field. Normally researchers do smaller electron-scale simulations of the plasma. But the Cray X1E supercomputer at ORNL has allowed us to combine electron-scale and ion-scale simulations to produce a much closer approximation of turbulence fluxes for various temperatures and densities. Modeling these instabilities on the actual reactor would be very time-consuming and expensive."
"ORNL is the nation's largest computing resource for big, open science," said Doug Kothe, director of science for ORNL's National Center for Computational Sciences. "As part of DOE's recently expanded INCITE program, time on our Cray X1E 'Phoenix' and Cray XT3 'Jaguar' supercomputers is being allotted to scientists from General Atomics and other organizations doing challenging, high-impact research that requires leadership-class computing resources. Breakthrough science becomes possible because of the systems expertise provided by the collaboration between Cray and ORNL staff and researchers."
A fusion reactor spins plasma at a high rate of speed, building up pressure and immense heat that can reach 200 million degrees Fahrenheit. Gyrokinetic physics is employed to study how these conditions cause instabilities that make the plasma slow down and cool. The equations involved in gyrokinetic calculations such as those performed by the General Atomics GYRO code were originally developed by researchers over 25 years ago. However, it has only been in the last few years that computers have become powerful enough to produce useful gyrokinetic simulations for fusion research.
To completely model the plasma in one of the donut-shaped reactors known as tokamaks where fusion research is conducted, the GYRO simulations will need to be included in still more complex models that take into account the engineering aspects of the reactors. General Atomics is also conducting fundamental research on the alpha particles produced by reactors that tend to slow down the plasma reaction. The ultimate goal is to design a much larger reactor that can confine the plasma in near-perfect thermal equilibrium and sustain the intense heat required for commercial power generation.
"Gryokinetic simulations place a tremendous amount of stress on a supercomputer's architecture," said Cray chief technology officer Steve Scott. "The Cray X1E system at ORNL is built with powerful vector processors sharing a common global memory and fed by massive memory and interconnect bandwidth. We are delighted that the General Atomics team and other INCITE participants have been able to take advantage of this advanced architecture to do the sort of large-scale, computationally demanding scientific work that was not previously possible."