More Lithium is Definitely Better

Increasing the amount of lithium coating in the wall of an experimental fusion reactor allows the plasma to be more easily contained. If plasma energy confinement is improved, a fusion reactor can, in principle, be made smaller and, therefore, cheaper. Adding more lithium also enhances certain plasma properties that aid the reaction.

“The lesson here for confining plasma is surprising and simple: When you use more and more lithium, the plasma confinement gets better and better,” said Rajesh Maingi, a physicist from the Oak Ridge National Laboratory (ORNL) who is on long-term assignment to PPPL. “This is not what we expected to see. We thought the effect would taper off at some point. But it doesn't. When it comes to fusion plasmas, it's “the more, the merrier.’ Sometimes, however, the containment of impurities becomes too good, so we're working on ejecting those impurities.”

Image Credit: F. Scotti and B. Davis, PPPL
As more lithium is added the plasma light changes from red to green and the overall light levels decrease. There is also progressive elimination of turbulent filaments (the helical striations barely visible on the non-lithium/red image) as the lithium increases.

In addition to Rajesh Maingi, other principal researchers on the effort included Stanley Kaye and Charles Skinner from PPPL; D.P. Boyle from Princeton University; and,  J.M. Canik from ORNL.

  Video: No Lithium - Red, Turbulent, High Light Level
  Video: Lithium - Green, Low Turbulence, Low Light Level
  With Lithium, More is Definitely Better
  "Continuous Improvement of H-Mode Discharge Performance with Progressively Increasing Lithium Coatings in the National Spherical Torus Experiment," Phys. Rev. Lett. 107, 145004 (2011)