National Energy Research Scientific Computing Center

Science Highlights 33
33
Stabilizing a Tokamak Plasma
3D Extended MHD Simulation of Fusion Plasmas
FES—Fusion SciDAC
OBJECTIVE
To use 3D simulations to gain new insights into the behavior of fusion plasmas and find
improved methods for ensuring plasma stability in future tokamak reactors.
Principal Investigator:
Stephen Jardin, Princeton Plasma
Physics Laboratory
FINDINGS/ACCOMPLISHMENTS
A team of physicists from Princeton Plasma Physics Laboratory, General Atomics and
the Max Planck Institute for Plasma Physics used NERSC’s Edison computer to discover
a mechanism that prevents the electrical current flowing through fusion plasma from
repeatedly peaking and crashing. This behavior is known as a “sawtooth cycle” and can
cause instabilities within the plasma’s core.
Learning how to model and study the behavior of fusion plasmas has important
implications for ITER, the multinational fusion facility being constructed in France to
demonstrate the practicality of fusion power. Instabilities in the plasma could destabilize
and halt the fusion process. Preventing the destabilizing cycle from starting would
therefore be highly beneficial for the ITER experiment and future tokamak reactors.
RESEARCH DETAILS
Running M3D-C1—a program that creates 3D simulations of fusion plasmas—on
Edison, researchers found that under certain conditions a helix-shaped whirlpool of
plasma forms around the center of the tokamak. The swirling plasma acts like a
dynamo—a moving fluid that creates electric and magnetic fields. Together these fields
prevent the current flowing through plasma from peaking and crashing.
During the simulations the scientists were able to virtually add new diagnostics, or
probes, to the computer code, which measure the helical velocity fields, electric
potential, and magnetic fields to clarify how the dynamo forms and persists. The
persistence produces the voltage in the center of the discharge that keeps the plasma
current from peaking.
A cross-section of the virtual plasma
showing where the magnetic field lines
intersect the plane. The central section
has field lines that rotate exactly once.
Image: Stephen Jardin, Princeton
Plasma Physics Laboratory
Publication:
S. C. Jardin, N. Ferraro, and I. Krebs,
“Self-Organized Stationary States of
Tokamaks,” Phys. Rev. Lett. 115, 215001,
November 17, 2015; DOI: http://dx.doi.
org/10.1103/PhysRevLett.115.215001
Full Story:
http://bit.ly/NERSCarTokamakPlasma