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--By Raphael Rosen

Scientists at the US Department of Energy's Princeton Plasma Physics Laboratory (PPPL) have helped design and test a component that could improve the performance of doughnut-shaped fusion facilities known as tokamaks.

Called a "liquid lithium limiter," the device has circulated the protective liquid metal within the walls of China's Experimental Advanced Superconducting Tokamak (EAST) and kept the plasma from cooling down and halting fusion reactions. The journal Nuclear Fusion published results of the experiment in March 2016.

This system reduces the production of impurities that typically are created when the plasma reaches other components of the vessel. Moreover, plasmas tolerate higher amounts of lithium impurities, compared with the impurities from other materials, because the low atomic number of lithium produces very low amounts of plasma radiation that typically cools the plasma core.

Serving as the main point of contact with plasma enables the lithium to absorb the hot deuterium ions that drift from the centre of the plasma, and keeps them from striking the interior walls of the tokamak and cooling down. Limiting the amount of cool deuterium at the edge of the plasma reduces the difference in temperature between the hot plasma centre and the cooler edge, and reduces turbulence. As a side note, however, contact with the ions was found to slightly damage the thin stainless steel foil surface of the limiter device, prompting work on an improved design.

Read the full report on the PPPL website.

Photo of the white-hot limiter glowing in contact with the plasma during an EAST discharge.