Lithium coating on graphite plasma facing components has been known as effective method for suppression of impurities and for reduction of hydrogen content. Recent research from an internation team comprision of researchers from US, Japan and France, have found an explanation why ultra-thin lithium films leads to improved hydrogen-recycling.
In Physical Review letters, the team led by Predrag S. Krstic of JICS and Jean Paul Allain of Purdue University explained that oxygen plays a key role in how lithium coatings on graphite surfaces control plasma behavior.
The strong coupling between the plasma edge and the wall surface causes erosion of the wall material, retention of radioactive tritium and pollution of the plasma. Therefore, an understanding of the processes that involve the uptake and release of deuterium and tritium are important. The paper shows that oxygen plays the key role in trapping deuterium, while lithium's main role is to bring and retain the oxygen to the surface. Deuterium atoms preferentially bind with oxygen and carbon-oxygen when there is a comparable amount of oxygen to lithium at the surface.
Lithium conditioning experiments in tokamaks were started in 1990 after the achievement of high plasma confinement. The published paper may be a next step in influence on plasma behavior, including control of hydrogen recycling. This is an important issue in the construction of ITER and future magnetic fusion energy devices.
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