Synopsis: Good News for Stellarators

New simulations of an alternate fusion reactor design reveal that it can be stable against turbulent fluctuations.
Synopsis figure
P. Xanthopoulos/ Max Planck Institute for Plasma Physics

Fusion reactor experiments come in two shapes: the “plain-donut” tokamak and the “curly-donut” stellarator. The simpler-to-implement tokamak design is currently more popular, but engineers are now overcoming some of the challenges in building stellarators. New simulations reveal that the stellarator concept may benefit from inherent stability mechanisms that reduce the effects of turbulence. This could be good news for a recently built stellarator in Germany.

Both the tokamak and stellarator designs use magnetic coils to confine hot plasma in a ring-shaped volume, or torus. For this confinement to work, the magnetic field lines generated by the coils and moving plasma need to spiral or twist as they loop around the ring. The tokamak creates this twisting by inducing currents within the plasma, while the stellarator uses warped magnetic coils. Although difficult to construct, the stellarator benefits from a long operation cycle and the absence of current-driven instabilities.

However, the warped geometry of a stellarator leads to high temperature gradients that produce turbulence. The worry is that strong turbulent fluctuations will cause plasma to escape. To investigate this problem, Pavlos Xanthopoulos and his colleagues at the Max Planck Institute for Plasma Physics (IPP), Germany, have performed computer simulations of a proposed stellarator design called QUASAR. When turbulent eddies are small relative to the variation length of the magnetic field, the team found that strong turbulent fluctuations were restricted to thin bands within the donut volume, so that the overall plasma loss was modest. For large eddies, the stellarator’s asymmetric magnetic field suppressed the strength of the fluctuations. The authors propose that this turbulence stabilization could be verified in the IPP’s Wendelstein 7-X stellarator, which started operation in February 2016.

This research is published in Physical Review X.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics based in Lyon, France.


Features

More Features »

Announcements

More Announcements »

Subject Areas

Energy ResearchPlasma Physics

Previous Synopsis

Acoustics

Bang a Gong

Read More »

Next Synopsis

Quantum Physics

Cavity-Controlled Chemistry

Read More »

Related Articles

Focus: Folded Solar Panel Opens Without Power Source
Energy Research

Focus: Folded Solar Panel Opens Without Power Source

A spacecraft solar cell design uses a temperature-sensitive polymer to expand the panel’s surface area by 10 times in 40 seconds. Read More »

Viewpoint: Cooling with a Squeeze
Materials Science

Viewpoint: Cooling with a Squeeze

A newly designed alloy exhibits a “colossal” elastocaloric effect—a temperature change under strain—making it a good candidate for an environmentally friendly type of cooling. Read More »

Viewpoint: Plot Thickens in Solar Opacity Debate
Plasma Physics

Viewpoint: Plot Thickens in Solar Opacity Debate

Experiments that replicate conditions in the Sun’s interior have found that the light absorption by certain elements doesn’t match expectations, raising questions about the accuracy of solar models. Read More »

More Articles