Jan. 3, 2019  — In 1934, physicist Ernest Rutherford and his colleagues produced the first fusion reaction—the fusing of light nuclei to release energy—in a laboratory by converting deuterium, a heavy hydrogen isotope, to helium.

Since then, scientists have built increasingly efficient fusion energy devices with a goal to achieve net fusion energy, or useable power. Today, the world’s largest fusion experiment is being built by seven international members, including the United States. The ITER fusion facility is expected to produce 10 times more power than the thermal power required to heat the plasma, thereby demonstrating the feasibility of commercial-scale fusion power.

If fusion power plants become a reality, they could provide nearly inexhaustible energy using fuel derived from seawater—a globally abundant source of deuterium, and a similarly abundant source of lithium.

But fusion has some stellar challenges to overcome first. Hot, gaseous plasma formed in a fusion device reaches extreme temperatures higher than the core of the Sun, nature’s fusion factory. Electric currents running through the plasma rip apart hydrogen nuclei into their constituent ions and electrons.

Because of these extreme and remote conditions, plasma behavior is difficult to study experimentally, and scientists often must fuse experiment with computational simulations to understand fusion processes.

That’s why a team of scientists—including Christopher Holland of the University of California San Diego, Jeff Candy of General Atomics, and Nathan Howard of MIT—are using the world’s smartest and fastest supercomputer, the 200-petaflop IBM AC922 Summit system at the Oak Ridge Leadership Computing Facility (OLCF), to better understand turbulence, an important characteristic of plasma behavior that affects performance in fusion devices such as ITER.

The OLCF is a US Department of Energy (DOE) Office of Science User Facility located at DOE’s Oak Ridge National Laboratory.

Following an Innovative and Novel Computational Impact on Theory and Experiment (INCITE) project led by Holland on the Cray XK7 Titan supercomputer—Summit’s 27-petaflop predecessor at the OLCF that was decommissioned in 2019—Candy is leading an Advanced Scientific Computing Research Leadership Computing Challenge project on Summit.

Turbulence in a tokamak

Many fusion devices use superconducting magnets to confine plasma in a tokamak, a donut-shaped vessel. The tokamak’s design allows magnetic field lines to run in two directions, long and short, through the plasma.

“As charged ions and electrons move around those field lines, they spin in a helix motion. The radius of this motion is known as the gyroradius,” Holland said.

The heavier ions throw their mass around more and create a larger gyroradius than that of the much lighter electrons. But as the ions and electrons spin along the magnetic field, they also push and pull on each other across the field, leading to fluctuations in ion and electron speed and energy. These energized wobbles result in turbulence that can rapidly transport heat away from the plasma center, reducing the number of fusion reactions that occur. Turbulence at one scale can inhibit or enhance turbulent fluctuations on other scales, impacting heat transport and, therefore, fusion performance.

“Standard plasma turbulence simulations only capture wavelengths at the ion scale, which is about 60 times bigger than the electron scale,” Howard said. “But we’ve found that simulating the larger scale alone is ineffective for explaining heat losses. We need both the long and short wavelengths in turbulence to explain levels of heat loss observed in experiment.”

To read the complete article, visit: https://www.olcf.ornl.gov/2020/01/02/speeding-toward-the-future-of-fusion/

Related Publication: J. Candy, I. Sfiligoi, E. A. Belli, K. Hallatschek, C. Holland, N. T. Howard, and E. D’Azevedo, “Multiscale-Optimized Plasma Turbulence Simulation on Petascale Architectures.” Computers and Fluids 188 (2019): 125, doi:10.1016/j.compfluid.2019.04.016.

About the Oak Ridge National Laboratory 

UT-Battelle LLC manages Oak Ridge National Laboratory for DOE’s Office of Science, the single largest supporter of basic research in the physical sciences in the United States. DOE’s Office of Science is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science.

About the DIII-D National Fusion Facility

DIII-D is the largest magnetic fusion research facility in the U.S. and has been the site of numerous pioneering contributions to the development of fusion energy science. DIII-D continues the drive toward practical fusion energy with critical research conducted in collaboration with more than 600 scientists representing over 100 institutions worldwide. For more information, visit www.ga.com/diii-d.

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Source: Katie Elyce Jones, Oak Ridge National Laboratory