LITHIUM WALL CONDITIONING FOR FUEL AND IMPURITY CONTROL

Small-scale laboratory experiments on wall conditioning by thin lithiu m layer deposition are carried out. Suppression of carbon impurities b y lithium deposition onto graphite walls are clearly demonstrated by a glow discharge in 1% oxygen in helium. Strong gettering effects of cl ean lithium surfaces on oxygen and hydrogen atoms are found, supportin g recent findings in fusion devices. The maximum number of H atoms pum ped 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 equilibr ium state. Furthermore, most of the hydrogens pumped by the lithium la yer are desorbed as H-2 molecules at relatively low temperatures such as 200 degrees C. This thermal desorption study suggests a very slow f ormation of lithium hydride whose thermal decomposition takes place at approximate to 700 degrees C. Copyright (C) 1996 Elsevier Science Ltd .