Lithium wall conditioning for fuel and impurity control

Small-scale laboratory experiments on wall conditioning by thin lithium layer deposition are carried out. Suppression of carbon impurities by lithium deposition onto graphite walls are clearly demonstrated by a glow discharge in 1% oxygen in helium. Strong gettering effects of clean lithium surfaces on oxygen and hydrogen atoms are found, supporting recent findings in fusion devices. The maximum number of H atoms pumped by the lithium layer at room temperature is approximately equal to the number of Li atoms in the vessel. Thus, the effective solubility of hydrogen in lithium is as high as H/(Li+H) approximate to 50% which is orders of magnitude larger than the values in the thermal equilibrium state. Furthermore, most of the hydrogens pumped by the lithium layer are desorbed as H-2 molecules at relatively low temperatures such as 200 degrees C. This thermal desorption study suggests a very slow formation of lithium hydride whose thermal decomposition takes place at approximate to 700 degrees C. Copyright (C) 1996 Elsevier Science Ltd.