Physicists uncover mechanism that stabilizes plasma within tokamaks November 10, 2015

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.

A team of physicists led by Stephen Jardin of the U.S. Department of Energy's Princeton Plasma Physics Laboratory (PPPL) has discovered 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. The results have been accepted for publication in Physical Review Letters. The research was supported by the DOE Office of Science (Office of Fusion Energy Sciences).
The researchers found two specific conditions under which the plasma behaves like a dynamo. First, the magnetic lines that circle the plasma must rotate exactly once, both the long way and the short way around the doughnut-shaped configuration, so an electron or ion following a magnetic field line would end up exactly where it began (Figure 1). Second, the pressure in the center of the plasma must be significantly greater than at the edge, creating a gradient between the two sections. This gradient combines with the rotating magnetic field lines to create spinning rolls of plasma that swirl around the tokamak and gives rise to the dynamo that maintains equilibrium and produces stability.

Read more at: http://phys.org/news/2015-11-physicists-uncover-mechanism-stabilizes-plasma.html#jCp